path: root/man-pages-posix-2003/man1p/awk.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "AWK" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" awk 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
awk \- pattern scanning and processing language
.SH SYNOPSIS
.LP
\fBawk\fP \fB[\fP\fB-F\fP \fIERE\fP\fB][\fP\fB-v\fP \fIassignment\fP\fB]\fP
\fB\&...\fP \fIprogram\fP
\fB[\fP\fIargument\fP \fB...\fP\fB]\fP\fB
.br
.sp
awk\fP \fB[\fP\fB-F\fP \fIERE\fP\fB]\fP \fB-f\fP \fIprogfile\fP \fB...\fP
\fB[\fP\fB-v\fP
\fIassignment\fP\fB]\fP \fB...\fP\fB[\fP\fIargument\fP \fB...\fP\fB]\fP\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIawk\fP utility shall execute programs written in the \fIawk\fP
programming language, which is specialized for textual
data manipulation. An \fIawk\fP program is a sequence of patterns
and corresponding actions. When input is read that matches a
pattern, the action associated with that pattern is carried out.
.LP
Input shall be interpreted as a sequence of records. By default, a
record is a line, less its terminating <newline>, but
this can be changed by using the \fBRS\fP built-in variable. Each
record of input shall be matched in turn against each pattern in
the program. For each pattern matched, the associated action shall
be executed.
.LP
The \fIawk\fP utility shall interpret each input record as a sequence
of fields where, by default, a field is a string of non-
<blank>s. This default white-space field delimiter can be changed
by using the \fBFS\fP built-in variable or \fB-F\fP
\fIERE\fP. The \fIawk\fP utility shall denote the first field in a
record $1, the second $2, and so on. The symbol $0 shall refer
to the entire record; setting any other field causes the re-evaluation
of $0. Assigning to $0 shall reset the values of all other
fields and the \fBNF\fP built-in variable.
.SH OPTIONS
.LP
The \fIawk\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following options shall be supported:
.TP 7
\fB-F\ \fP \fIERE\fP
Define the input field separator to be the extended regular expression
\fIERE\fP, before any input is read; see Regular Expressions .
.TP 7
\fB-f\ \fP \fIprogfile\fP
Specify the pathname of the file \fIprogfile\fP containing an \fIawk\fP
program. If multiple instances of this option are
specified, the concatenation of the files specified as \fIprogfile\fP
in the order specified shall be the \fIawk\fP program. The
\fIawk\fP program can alternatively be specified in the command line
as a single argument.
.TP 7
\fB-v\ \fP \fIassignment\fP
The application shall ensure that the \fIassignment\fP argument is
in the same form as an \fIassignment\fP operand. The specified
variable assignment shall occur prior to executing the \fIawk\fP program,
including the actions associated with \fBBEGIN\fP
patterns (if any). Multiple occurrences of this option can be specified.
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIprogram\fP
If no \fB-f\fP option is specified, the first operand to \fIawk\fP
shall be the text of the \fIawk\fP program. The
application shall supply the \fIprogram\fP operand as a single argument
to \fIawk\fP. If the text does not end in a
<newline>, \fIawk\fP shall interpret the text as if it did.
.TP 7
\fIargument\fP
Either of the following two types of \fIargument\fP can be intermixed:
.TP 7
\fIfile\fP
.RS
A pathname of a file that contains the input to be read, which is
matched against the set of patterns in the program. If no
\fIfile\fP operands are specified, or if a \fIfile\fP operand is \fB'-'\fP,
the standard input shall be used.
.RE
.TP 7
\fIassignment\fP
.RS
An operand that begins with an underscore or alphabetic character
from the portable character set (see the table in the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, Section 6.1, Portable
Character Set), followed by a sequence of underscores, digits, and
alphabetics from the portable character set, followed by the
\fB'='\fP character, shall specify a variable assignment rather than
a pathname. The characters before the \fB'='\fP
represent the name of an \fIawk\fP variable; if that name is an \fIawk\fP
reserved word (see Grammar ) the behavior is undefined. The characters
following the equal sign shall be interpreted as if they
appeared in the \fIawk\fP program preceded and followed by a double-quote
( \fB' )'\fP character, as a \fBSTRING\fP token (see
Grammar ), except that if the last character is an unescaped backslash,
it shall be interpreted as a
literal backslash rather than as the first character of the sequence
\fB"\\""\fP . The variable shall be assigned the value of
that \fBSTRING\fP token and, if appropriate, shall be considered a
\fInumeric string\fP (see Expressions in awk ), the variable shall
also be assigned its numeric value. Each such variable assignment
shall occur just prior to the processing of the following \fIfile\fP,
if any. Thus, an assignment before the first \fIfile\fP
argument shall be executed after the \fBBEGIN\fP actions (if any),
while an assignment after the last \fIfile\fP argument shall
occur before the \fBEND\fP actions (if any). If there are no \fIfile\fP
arguments, assignments shall be executed before
processing the standard input.
.RE
.sp
.sp
.SH STDIN
.LP
The standard input shall be used only if no \fIfile\fP operands are
specified, or if a \fIfile\fP operand is \fB'-'\fP ;
see the INPUT FILES section. If the \fIawk\fP program contains no
actions and no patterns, but is otherwise a valid \fIawk\fP
program, standard input and any \fIfile\fP operands shall not be read
and \fIawk\fP shall exit with a return status of zero.
.SH INPUT FILES
.LP
Input files to the \fIawk\fP program from any of the following sources
shall be text files:
.IP " *" 3
Any \fIfile\fP operands or their equivalents, achieved by modifying
the \fIawk\fP variables \fBARGV\fP and \fBARGC\fP
.LP
.IP " *" 3
Standard input in the absence of any \fIfile\fP operands
.LP
.IP " *" 3
Arguments to the \fBgetline\fP function
.LP
.LP
Whether the variable \fBRS\fP is set to a value other than a <newline>
or not, for these files, implementations shall
support records terminated with the specified separator up to {LINE_MAX}
bytes and may support longer records.
.LP
If \fB-f\fP \fIprogfile\fP is specified, the application shall ensure
that the files named by each of the \fIprogfile\fP
option-arguments are text files and their concatenation, in the same
order as they appear in the arguments, is an \fIawk\fP
program.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIawk\fP:
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_COLLATE\fP
Determine the locale for the behavior of ranges, equivalence classes,
and multi-character collating elements within regular
expressions and in comparisons of string values.
.TP 7
\fILC_CTYPE\fP
Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files), the
behavior of character classes within regular expressions, the
identification of characters as letters, and the mapping of uppercase
and lowercase characters for the \fBtoupper\fP and
\fBtolower\fP functions.
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fILC_NUMERIC\fP
Determine the radix character used when interpreting numeric input,
performing conversions between numeric and string values, and
formatting numeric output. Regardless of locale, the period character
(the decimal-point character of the POSIX locale) is the
decimal-point character recognized in processing \fIawk\fP programs
(including assignments in command line arguments).
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fIPATH\fP
Determine the search path when looking for commands executed by \fIsystem\fP(\fIexpr\fP),
or input and output pipes; see the
Base Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter 8, Environment
Variables.
.sp
.LP
In addition, all environment variables shall be visible via the \fIawk\fP
variable \fBENVIRON\fP.
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
The nature of the output files depends on the \fIawk\fP program.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
The nature of the output files depends on the \fIawk\fP program.
.SH EXTENDED DESCRIPTION
.SS Overall Program Structure
.LP
An \fIawk\fP program is composed of pairs of the form:
.sp
.RS
.nf

\fIpattern\fP \fB{\fP \fIaction\fP \fB}
\fP
.fi
.RE
.LP
Either the pattern or the action (including the enclosing brace characters)
can be omitted.
.LP
A missing pattern shall match any record of input, and a missing action
shall be equivalent to:
.sp
.RS
.nf

\fB{ print }
\fP
.fi
.RE
.LP
Execution of the \fIawk\fP program shall start by first executing
the actions associated with all \fBBEGIN\fP patterns in the
order they occur in the program. Then each \fIfile\fP operand (or
standard input if no files were specified) shall be processed in
turn by reading data from the file until a record separator is seen
( <newline> by default). Before the first reference to a
field in the record is evaluated, the record shall be split into fields,
according to the rules in Regular Expressions, using the value of
\fBFS\fP that was current at the time the record was read. Each
pattern in the program then shall be evaluated in the order of occurrence,
and the action associated with each pattern that matches
the current record executed. The action for a matching pattern shall
be executed before evaluating subsequent patterns. Finally,
the actions associated with all \fBEND\fP patterns shall be executed
in the order they occur in the program.
.SS Expressions in awk
.LP
Expressions describe computations used in \fIpatterns\fP and \fIactions\fP.
In the following table, valid expression
operations are given in groups from highest precedence first to lowest
precedence last, with equal-precedence operators grouped
between horizontal lines. In expression evaluation, where the grammar
is formally ambiguous, higher precedence operators shall be
evaluated before lower precedence operators. In this table \fIexpr\fP,
\fIexpr1\fP, \fIexpr2\fP, and \fIexpr3\fP represent any
expression, while lvalue represents any entity that can be assigned
to (that is, on the left side of an assignment operator). The
precise syntax of expressions is given in Grammar .
.sp
.ce 1
\fBTable: Expressions in Decreasing Precedence in \fIawk\fP\fP
.TS C
center; l1 l1 l1 l.
\fBSyntax\fP	\fBName\fP	\fBType of Result\fP	\fBAssociativity\fP
( \fIexpr\fP )	Grouping	Type of \fIexpr\fP	N/A
$\fIexpr\fP	Field reference	String	N/A
++ lvalue	Pre-increment	Numeric	N/A
-- lvalue	Pre-decrement	Numeric	N/A
lvalue ++	Post-increment	Numeric	N/A
lvalue --	Post-decrement	Numeric	N/A
\fIexpr\fP ^ \fIexpr\fP	Exponentiation	Numeric	Right
! \fIexpr\fP	Logical not	Numeric	N/A
+ \fIexpr\fP	Unary plus	Numeric	N/A
- \fIexpr\fP	Unary minus	Numeric	N/A
\fIexpr\fP * \fIexpr\fP	Multiplication	Numeric	Left
\fIexpr\fP / \fIexpr\fP	Division	Numeric	Left
\fIexpr\fP % \fIexpr\fP	Modulus	Numeric	Left
\fIexpr\fP + \fIexpr\fP	Addition	Numeric	Left
\fIexpr\fP - \fIexpr\fP	Subtraction	Numeric	Left
\fIexpr\fP \fIexpr\fP	String concatenation	String	Left
\fIexpr\fP < \fIexpr\fP	Less than	Numeric	None
\fIexpr\fP <= \fIexpr\fP	Less than or equal to	Numeric	None
\fIexpr\fP != \fIexpr\fP	Not equal to	Numeric	None
\fIexpr\fP == \fIexpr\fP	Equal to	Numeric	None
\fIexpr\fP > \fIexpr\fP	Greater than	Numeric	None
\fIexpr\fP >= \fIexpr\fP	Greater than or equal to	Numeric	None
\fIexpr\fP ~ \fIexpr\fP	ERE match	Numeric	None
\fIexpr\fP !~ \fIexpr\fP	ERE non-match	Numeric	None
\fIexpr\fP in array	Array membership	Numeric	Left
( \fIindex\fP ) in \fIarray\fP	Multi-dimension array	Numeric	Left
\ 	membership	\ 	\ 
\fIexpr\fP && \fIexpr\fP	Logical AND	Numeric	Left
\fIexpr\fP || \fIexpr\fP	Logical OR	Numeric	Left
\fIexpr1\fP ? \fIexpr2\fP : \fIexpr3\fP	Conditional expression	Type of selected	Right
\ 	\ 	\fIexpr2\fP or \fIexpr3\fP	\ 
lvalue ^= \fIexpr\fP	Exponentiation assignment	Numeric	Right
lvalue %= \fIexpr\fP	Modulus assignment	Numeric	Right
lvalue *= \fIexpr\fP	Multiplication assignment	Numeric	Right
lvalue /= \fIexpr\fP	Division assignment	Numeric	Right
lvalue += \fIexpr\fP	Addition assignment	Numeric	Right
lvalue -= \fIexpr\fP	Subtraction assignment	Numeric	Right
lvalue = \fIexpr\fP	Assignment	Type of \fIexpr\fP	Right
.TE
.LP
Each expression shall have either a string value, a numeric value,
or both. Except as stated for specific contexts, the value of
an expression shall be implicitly converted to the type needed for
the context in which it is used. A string value shall be
converted to a numeric value by the equivalent of the following calls
to functions defined by the ISO\ C standard:
.sp
.RS
.nf

\fBsetlocale(LC_NUMERIC, "");
\fP\fInumeric_value\fP \fB= atof(\fP\fIstring_value\fP\fB);
\fP
.fi
.RE
.LP
A numeric value that is exactly equal to the value of an integer (see
\fIConcepts Derived
from the ISO C Standard\fP ) shall be converted to a string by the
equivalent of a call to the \fBsprintf\fP function (see String Functions
) with the string \fB"%d"\fP as the \fIfmt\fP argument and the numeric
value being
converted as the first and only \fIexpr\fP argument. Any other numeric
value shall be converted to a string by the equivalent of a
call to the \fBsprintf\fP function with the value of the variable
\fBCONVFMT\fP as the \fIfmt\fP argument and the numeric value
being converted as the first and only \fIexpr\fP argument. The result
of the conversion is unspecified if the value of
\fBCONVFMT\fP is not a floating-point format specification. This volume
of IEEE\ Std\ 1003.1-2001 specifies no explicit
conversions between numbers and strings. An application can force
an expression to be treated as a number by adding zero to it, or
can force it to be treated as a string by concatenating the null string
( \fB""\fP ) to it.
.LP
A string value shall be considered a \fInumeric string\fP if it comes
from one of the following:
.IP " 1." 4
Field variables
.LP
.IP " 2." 4
Input from the \fIgetline\fP() function
.LP
.IP " 3." 4
\fBFILENAME\fP
.LP
.IP " 4." 4
\fBARGV\fP array elements
.LP
.IP " 5." 4
\fBENVIRON\fP array elements
.LP
.IP " 6." 4
Array elements created by the \fIsplit\fP() function
.LP
.IP " 7." 4
A command line variable assignment
.LP
.IP " 8." 4
Variable assignment from another numeric string variable
.LP
.LP
and after all the following conversions have been applied, the resulting
string would lexically be recognized as a \fBNUMBER\fP
token as described by the lexical conventions in Grammar :
.IP " *" 3
All leading and trailing <blank>s are discarded.
.LP
.IP " *" 3
If the first non- <blank> is \fB'+'\fP or \fB'-'\fP, it is discarded.
.LP
.IP " *" 3
Changing each occurrence of the decimal point character from the current
locale to a period.
.LP
.LP
If a \fB'-'\fP character is ignored in the preceding description,
the numeric value of the \fInumeric string\fP shall be the
negation of the numeric value of the recognized \fBNUMBER\fP token.
Otherwise, the numeric value of the \fInumeric string\fP
shall be the numeric value of the recognized \fBNUMBER\fP token. Whether
or not a string is a \fInumeric string\fP shall be
relevant only in contexts where that term is used in this section.
.LP
When an expression is used in a Boolean context, if it has a numeric
value, a value of zero shall be treated as false and any
other value shall be treated as true. Otherwise, a string value of
the null string shall be treated as false and any other value
shall be treated as true. A Boolean context shall be one of the following:
.IP " *" 3
The first subexpression of a conditional expression
.LP
.IP " *" 3
An expression operated on by logical NOT, logical AND, or logical
OR
.LP
.IP " *" 3
The second expression of a \fBfor\fP statement
.LP
.IP " *" 3
The expression of an \fBif\fP statement
.LP
.IP " *" 3
The expression of the \fBwhile\fP clause in either a \fBwhile\fP or
\fBdo\fP... \fBwhile\fP statement
.LP
.IP " *" 3
An expression used as a pattern (as in Overall Program Structure)
.LP
.LP
All arithmetic shall follow the semantics of floating-point arithmetic
as specified by the ISO\ C standard (see \fIConcepts Derived from
the ISO C Standard\fP ).
.LP
The value of the expression:
.sp
.RS
.nf

\fIexpr1\fP \fB^\fP \fIexpr2\fP
.fi
.RE
.LP
shall be equivalent to the value returned by the ISO\ C standard function
call:
.sp
.RS
.nf

\fBpow(\fP\fIexpr1\fP\fB,\fP \fIexpr2\fP\fB)
\fP
.fi
.RE
.LP
The expression:
.sp
.RS
.nf

\fBlvalue ^=\fP \fIexpr\fP
.fi
.RE
.LP
shall be equivalent to the ISO\ C standard expression:
.sp
.RS
.nf

\fBlvalue = pow(lvalue,\fP \fIexpr\fP\fB)
\fP
.fi
.RE
.LP
except that lvalue shall be evaluated only once. The value of the
expression:
.sp
.RS
.nf

\fIexpr1\fP \fB%\fP \fIexpr2\fP
.fi
.RE
.LP
shall be equivalent to the value returned by the ISO\ C standard function
call:
.sp
.RS
.nf

\fBfmod(\fP\fIexpr1\fP\fB,\fP \fIexpr2\fP\fB)
\fP
.fi
.RE
.LP
The expression:
.sp
.RS
.nf

\fBlvalue %=\fP \fIexpr\fP
.fi
.RE
.LP
shall be equivalent to the ISO\ C standard expression:
.sp
.RS
.nf

\fBlvalue = fmod(lvalue,\fP \fIexpr\fP\fB)
\fP
.fi
.RE
.LP
except that lvalue shall be evaluated only once.
.LP
Variables and fields shall be set by the assignment statement:
.sp
.RS
.nf

\fBlvalue =\fP \fIexpression\fP
.fi
.RE
.LP
and the type of \fIexpression\fP shall determine the resulting variable
type. The assignment includes the arithmetic
assignments ( \fB"+="\fP, \fB"-="\fP, \fB"*="\fP, \fB"/="\fP,
\fB"%="\fP, \fB"^="\fP, \fB"++"\fP,
\fB"--"\fP ) all of which shall produce a numeric result. The left-hand
side of an assignment and the target of increment and
decrement operators can be one of a variable, an array with index,
or a field selector.
.LP
The \fIawk\fP language supplies arrays that are used for storing numbers
or strings. Arrays need not be declared. They shall
initially be empty, and their sizes shall change dynamically. The
subscripts, or element identifiers, are strings, providing a type
of associative array capability. An array name followed by a subscript
within square brackets can be used as an lvalue and thus as
an expression, as described in the grammar; see Grammar . Unsubscripted
array names can be used in
only the following contexts:
.IP " *" 3
A parameter in a function definition or function call
.LP
.IP " *" 3
The \fBNAME\fP token following any use of the keyword \fBin\fP as
specified in the grammar (see Grammar ); if the name used in this
context is not an array name, the behavior is undefined
.LP
.LP
A valid array \fIindex\fP shall consist of one or more comma-separated
expressions, similar to the way in which
multi-dimensional arrays are indexed in some programming languages.
Because \fIawk\fP arrays are really one-dimensional, such a
comma-separated list shall be converted to a single string by concatenating
the string values of the separate expressions, each
separated from the other by the value of the \fBSUBSEP\fP variable.
Thus, the following two index operations shall be
equivalent:
.sp
.RS
.nf

\fIvar\fP\fB[\fP\fIexpr1\fP\fB,\fP \fIexpr2\fP\fB, ...\fP \fIexprn\fP\fB]
.sp

\fP\fIvar\fP\fB[\fP\fIexpr1\fP \fBSUBSEP\fP \fIexpr2\fP \fBSUBSEP ... SUBSEP\fP \fIexprn\fP\fB]\fP
.fi
.RE
.LP
The application shall ensure that a multi-dimensioned \fIindex\fP
used with the \fBin\fP operator is parenthesized. The
\fBin\fP operator, which tests for the existence of a particular array
element, shall not cause that element to exist. Any other
reference to a nonexistent array element shall automatically create
it.
.LP
Comparisons (with the \fB'<'\fP, \fB"<="\fP, \fB"!="\fP, \fB"=="\fP,
\fB'>'\fP, and
\fB">="\fP operators) shall be made numerically if both operands are
numeric, if one is numeric and the other has a string
value that is a numeric string, or if one is numeric and the other
has the uninitialized value. Otherwise, operands shall be
converted to strings as required and a string comparison shall be
made using the locale-specific collation sequence. The value of
the comparison expression shall be 1 if the relation is true, or 0
if the relation is false.
.SS Variables and Special Variables
.LP
Variables can be used in an \fIawk\fP program by referencing them.
With the exception of function parameters (see User-Defined Functions
), they are not explicitly declared. Function parameter names shall
be local to the
function; all other variable names shall be global. The same name
shall not be used as both a function parameter name and as the
name of a function or a special \fIawk\fP variable. The same name
shall not be used both as a variable name with global scope and
as the name of a function. The same name shall not be used within
the same scope both as a scalar variable and as an array.
Uninitialized variables, including scalar variables, array elements,
and field variables, shall have an uninitialized value. An
uninitialized value shall have both a numeric value of zero and a
string value of the empty string. Evaluation of variables with an
uninitialized value, to either string or numeric, shall be determined
by the context in which they are used.
.LP
Field variables shall be designated by a \fB'$'\fP followed by a number
or numerical expression. The effect of the field
number \fIexpression\fP evaluating to anything other than a non-negative
integer is unspecified; uninitialized variables or string
values need not be converted to numeric values in this context. New
field variables can be created by assigning a value to them.
References to nonexistent fields (that is, fields after $\fBNF\fP),
shall evaluate to the uninitialized value. Such references
shall not create new fields. However, assigning to a nonexistent field
(for example, $(\fBNF\fP+2)=5) shall increase the value of
\fBNF\fP; create any intervening fields with the uninitialized value;
and cause the value of $0 to be recomputed, with the fields
being separated by the value of \fBOFS\fP. Each field variable shall
have a string value or an uninitialized value when created.
Field variables shall have the uninitialized value when created from
$0 using \fBFS\fP and the variable does not contain any
characters. If appropriate, the field variable shall be considered
a numeric string (see Expressions in
awk ).
.LP
Implementations shall support the following other special variables
that are set by \fIawk\fP:
.TP 7
\fBARGC\fP
The number of elements in the \fBARGV\fP array.
.TP 7
\fBARGV\fP
An array of command line arguments, excluding options and the \fIprogram\fP
argument, numbered from zero to \fBARGC\fP-1. 
.LP
The arguments in \fBARGV\fP can be modified or added to; \fBARGC\fP
can be altered. As each input file ends, \fIawk\fP shall
treat the next non-null element of \fBARGV\fP, up to the current value
of \fBARGC\fP-1, inclusive, as the name of the next input
file. Thus, setting an element of \fBARGV\fP to null means that it
shall not be treated as an input file. The name \fB'-'\fP
indicates the standard input. If an argument matches the format of
an \fIassignment\fP operand, this argument shall be treated as
an \fIassignment\fP rather than a \fIfile\fP argument.
.TP 7
\fBCONVFMT\fP
The \fBprintf\fP format for converting numbers to strings (except
for output statements, where \fBOFMT\fP is used);
\fB"%.6g"\fP by default.
.TP 7
\fBENVIRON\fP
An array representing the value of the environment, as described in
the \fIexec\fP functions defined in the System Interfaces
volume of IEEE\ Std\ 1003.1-2001. The indices of the array shall be
strings consisting of the names of the environment
variables, and the value of each array element shall be a string consisting
of the value of that variable. If appropriate, the
environment variable shall be considered a \fInumeric string\fP (see
Expressions in awk ); the
array element shall also have its numeric value. 
.LP
In all cases where the behavior of \fIawk\fP is affected by environment
variables (including the environment of any commands
that \fIawk\fP executes via the \fBsystem\fP function or via pipeline
redirections with the \fBprint\fP statement, the
\fBprintf\fP statement, or the \fBgetline\fP function), the environment
used shall be the environment at the time \fIawk\fP
began executing; it is implementation-defined whether any modification
of \fBENVIRON\fP affects this environment.
.TP 7
\fBFILENAME\fP
A pathname of the current input file. Inside a \fBBEGIN\fP action
the value is undefined. Inside an \fBEND\fP action the
value shall be the name of the last input file processed.
.TP 7
\fBFNR\fP
The ordinal number of the current record in the current file. Inside
a \fBBEGIN\fP action the value shall be zero. Inside an
\fBEND\fP action the value shall be the number of the last record
processed in the last file processed.
.TP 7
\fBFS\fP
Input field separator regular expression; a <space> by default.
.TP 7
\fBNF\fP
The number of fields in the current record. Inside a \fBBEGIN\fP action,
the use of \fBNF\fP is undefined unless a
\fBgetline\fP function without a \fIvar\fP argument is executed previously.
Inside an \fBEND\fP action, \fBNF\fP shall retain
the value it had for the last record read, unless a subsequent, redirected,
\fBgetline\fP function without a \fIvar\fP argument
is performed prior to entering the \fBEND\fP action.
.TP 7
\fBNR\fP
The ordinal number of the current record from the start of input.
Inside a \fBBEGIN\fP action the value shall be zero. Inside
an \fBEND\fP action the value shall be the number of the last record
processed.
.TP 7
\fBOFMT\fP
The \fBprintf\fP format for converting numbers to strings in output
statements (see Output
Statements ); \fB"%.6g"\fP by default. The result of the conversion
is unspecified if the value of \fBOFMT\fP is not a
floating-point format specification.
.TP 7
\fBOFS\fP
The \fBprint\fP statement output field separation; <space> by default.
.TP 7
\fBORS\fP
The \fBprint\fP statement output record separator; a <newline> by
default.
.TP 7
\fBRLENGTH\fP
The length of the string matched by the \fBmatch\fP function.
.TP 7
\fBRS\fP
The first character of the string value of \fBRS\fP shall be the input
record separator; a <newline> by default. If
\fBRS\fP contains more than one character, the results are unspecified.
If \fBRS\fP is null, then records are separated by
sequences consisting of a <newline> plus one or more blank lines,
leading or trailing blank lines shall not result in empty
records at the beginning or end of the input, and a <newline> shall
always be a field separator, no matter what the value of
\fBFS\fP is.
.TP 7
\fBRSTART\fP
The starting position of the string matched by the \fBmatch\fP function,
numbering from 1. This shall always be equivalent to
the return value of the \fBmatch\fP function.
.TP 7
\fBSUBSEP\fP
The subscript separator string for multi-dimensional arrays; the default
value is implementation-defined.
.sp
.SS Regular Expressions
.LP
The \fIawk\fP utility shall make use of the extended regular expression
notation (see the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 9.4, Extended Regular Expressions)
except that it shall allow the use of C-language conventions for escaping
special characters within the EREs, as specified in the
table in the Base Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter
5, File
Format Notation ( \fB'\\\\'\fP, \fB'\\a'\fP, \fB'\\b'\fP, \fB'\\f'\fP,
\fB'\\n'\fP, \fB'\\r'\fP, \fB'\\t'\fP,
\fB'\\v'\fP ) and the following table; these escape sequences shall
be recognized both inside and outside bracket expressions.
Note that records need not be separated by <newline>s and string constants
can contain <newline>s, so even the
\fB"\\n"\fP sequence is valid in \fIawk\fP EREs. Using a slash character
within an ERE requires the escaping shown in the
following table.
.br
.sp
.ce 1
\fBTable: Escape Sequences in \fIawk\fP\fP
.TS C
center; l1 lw(30)1 lw(30).
\fBEscape\fP	T{
.na
\fB\ \fP
.ad
T}	T{
.na
\fB\ \fP
.ad
T}
\fBSequence\fP	T{
.na
\fBDescription\fP
.ad
T}	T{
.na
\fBMeaning\fP
.ad
T}
\\"	T{
.na
Backslash quotation-mark
.ad
T}	T{
.na
Quotation-mark character
.ad
T}
\\/	T{
.na
Backslash slash
.ad
T}	T{
.na
Slash character
.ad
T}
\\ddd	T{
.na
A backslash character followed by the longest sequence of one, two, or three octal-digit characters (01234567). If all of the digits are 0 (that is, representation of the NUL character), the behavior is undefined.
.ad
T}	T{
.na
The character whose encoding is represented by the one, two, or three-digit octal integer. Multi-byte characters require multiple, concatenated escape sequences of this type, including the leading \fB'\\'\fP for each byte.
.ad
T}
\\c	T{
.na
A backslash character followed by any character not described in this table or in the table in the Base Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter 5, File Format Notation ( \fB'\\\\'\fP, \fB'\\a'\fP, \fB'\\b'\fP, \fB'\\f'\fP, \fB'\\n'\fP, \fB'\\r'\fP, \fB'\\t'\fP, \fB'\\v'\fP ).
.ad
T}	T{
.na
Undefined
.ad
T}
.TE
.LP
A regular expression can be matched against a specific field or string
by using one of the two regular expression matching
operators, \fB'~'\fP and \fB"!~"\fP . These operators shall interpret
their right-hand operand as a regular
expression and their left-hand operand as a string. If the regular
expression matches the string, the \fB'~'\fP expression
shall evaluate to a value of 1, and the \fB"!~"\fP expression shall
evaluate to a value of 0. (The regular expression
matching operation is as defined by the term matched in the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, Section 9.1, Regular Expression
Definitions, where a match occurs on any part of the
string unless the regular expression is limited with the circumflex
or dollar sign special characters.) If the regular expression
does not match the string, the \fB'~'\fP expression shall evaluate
to a value of 0, and the \fB"!~"\fP expression
shall evaluate to a value of 1. If the right-hand operand is any expression
other than the lexical token \fBERE\fP, the string
value of the expression shall be interpreted as an extended regular
expression, including the escape conventions described above.
Note that these same escape conventions shall also be applied in determining
the value of a string literal (the lexical token
\fBSTRING\fP), and thus shall be applied a second time when a string
literal is used in this context.
.LP
When an \fBERE\fP token appears as an expression in any context other
than as the right-hand of the \fB'~'\fP or
\fB"!~"\fP operator or as one of the built-in function arguments described
below, the value of the resulting expression
shall be the equivalent of:
.sp
.RS
.nf

\fB$0 ~ /\fP\fIere\fP\fB/
\fP
.fi
.RE
.LP
The \fIere\fP argument to the \fBgsub\fP, \fBmatch\fP, \fBsub\fP functions,
and the \fIfs\fP argument to the \fBsplit\fP
function (see String Functions ) shall be interpreted as extended
regular expressions. These can be
either \fBERE\fP tokens or arbitrary expressions, and shall be interpreted
in the same manner as the right-hand side of the
\fB'~'\fP or \fB"!~"\fP operator.
.LP
An extended regular expression can be used to separate fields by using
the \fB-F\fP \fIERE\fP option or by assigning a string
containing the expression to the built-in variable \fBFS\fP. The default
value of the \fBFS\fP variable shall be a single
<space>. The following describes \fBFS\fP behavior:
.IP " 1." 4
If \fBFS\fP is a null string, the behavior is unspecified.
.LP
.IP " 2." 4
If \fBFS\fP is a single character:
.RS
.IP " a." 4
If \fBFS\fP is <space>, skip leading and trailing <blank>s; fields
shall be delimited by sets of one or more
<blank>s.
.LP
.IP " b." 4
Otherwise, if \fBFS\fP is any other character \fIc\fP, fields shall
be delimited by each single occurrence of \fIc\fP.
.LP
.RE
.LP
.IP " 3." 4
Otherwise, the string value of \fBFS\fP shall be considered to be
an extended regular expression. Each occurrence of a sequence
matching the extended regular expression shall delimit fields.
.LP
.LP
Except for the \fB'~'\fP and \fB"!~"\fP operators, and in the \fBgsub\fP,
\fBmatch\fP, \fBsplit\fP, and
\fBsub\fP built-in functions, ERE matching shall be based on input
records; that is, record separator characters (the first
character of the value of the variable \fBRS\fP, <newline> by default)
cannot be embedded in the expression, and no
expression shall match the record separator character. If the record
separator is not <newline>, <newline>s embedded in
the expression can be matched. For the \fB'~'\fP and \fB"!~"\fP operators,
and in those four built-in functions,
ERE matching shall be based on text strings; that is, any character
(including <newline> and the record separator) can be
embedded in the pattern, and an appropriate pattern shall match any
character. However, in all \fIawk\fP ERE matching, the use of
one or more NUL characters in the pattern, input record, or text string
produces undefined results.
.SS Patterns
.LP
A \fIpattern\fP is any valid \fIexpression\fP, a range specified by
two expressions separated by a comma, or one of the two
special patterns \fBBEGIN\fP or \fBEND\fP.
.SS Special Patterns
.LP
The \fIawk\fP utility shall recognize two special patterns, \fBBEGIN\fP
and \fBEND\fP. Each \fBBEGIN\fP pattern shall be
matched once and its associated action executed before the first record
of input is read (except possibly by use of the
\fBgetline\fP function-see Input/Output and General Functions - in
a prior \fBBEGIN\fP action) and
before command line assignment is done. Each \fBEND\fP pattern shall
be matched once and its associated action executed after the
last record of input has been read. These two patterns shall have
associated actions.
.LP
\fBBEGIN\fP and \fBEND\fP shall not combine with other patterns. Multiple
\fBBEGIN\fP and \fBEND\fP patterns shall be
allowed. The actions associated with the \fBBEGIN\fP patterns shall
be executed in the order specified in the program, as are the
\fBEND\fP actions. An \fBEND\fP pattern can precede a \fBBEGIN\fP
pattern in a program.
.LP
If an \fIawk\fP program consists of only actions with the pattern
\fBBEGIN\fP, and the \fBBEGIN\fP action contains no
\fBgetline\fP function, \fIawk\fP shall exit without reading its input
when the last statement in the last \fBBEGIN\fP action is
executed. If an \fIawk\fP program consists of only actions with the
pattern \fBEND\fP or only actions with the patterns
\fBBEGIN\fP and \fBEND\fP, the input shall be read before the statements
in the \fBEND\fP actions are executed.
.SS Expression Patterns
.LP
An expression pattern shall be evaluated as if it were an expression
in a Boolean context. If the result is true, the pattern
shall be considered to match, and the associated action (if any) shall
be executed. If the result is false, the action shall not be
executed.
.SS Pattern Ranges
.LP
A pattern range consists of two expressions separated by a comma;
in this case, the action shall be performed for all records
between a match of the first expression and the following match of
the second expression, inclusive. At this point, the pattern
range can be repeated starting at input records subsequent to the
end of the matched range.
.SS Actions
.LP
An action is a sequence of statements as shown in the grammar in Grammar
\&. Any single statement
can be replaced by a statement list enclosed in braces. The application
shall ensure that statements in a statement list are
separated by <newline>s or semicolons. Statements in a statement list
shall be executed sequentially in the order that they
appear.
.LP
The \fIexpression\fP acting as the conditional in an \fBif\fP statement
shall be evaluated and if it is non-zero or non-null,
the following statement shall be executed; otherwise, if \fBelse\fP
is present, the statement following the \fBelse\fP shall be
executed.
.LP
The \fBif\fP, \fBwhile\fP, \fBdo\fP... \fBwhile\fP, \fBfor\fP, \fBbreak\fP,
and \fBcontinue\fP statements are based on
the ISO\ C standard (see \fIConcepts Derived from the ISO C Standard\fP
), except
that the Boolean expressions shall be treated as described in Expressions
in awk , and except in the
case of:
.sp
.RS
.nf

\fBfor (\fP\fIvariable\fP \fBin\fP \fIarray\fP\fB)
\fP
.fi
.RE
.LP
which shall iterate, assigning each \fIindex\fP of \fIarray\fP to
\fIvariable\fP in an unspecified order. The results of
adding new elements to \fIarray\fP within such a \fBfor\fP loop are
undefined. If a \fBbreak\fP or \fBcontinue\fP statement
occurs outside of a loop, the behavior is undefined.
.LP
The \fBdelete\fP statement shall remove an individual array element.
Thus, the following code deletes an entire array:
.sp
.RS
.nf

\fBfor (index in array)
    delete array[index]
\fP
.fi
.RE
.LP
The \fBnext\fP statement shall cause all further processing of the
current input record to be abandoned. The behavior is
undefined if a \fBnext\fP statement appears or is invoked in a \fBBEGIN\fP
or \fBEND\fP action.
.LP
The \fBexit\fP statement shall invoke all \fBEND\fP actions in the
order in which they occur in the program source and then
terminate the program without reading further input. An \fBexit\fP
statement inside an \fBEND\fP action shall terminate the
program without further execution of \fBEND\fP actions. If an expression
is specified in an \fBexit\fP statement, its numeric
value shall be the exit status of \fIawk\fP, unless subsequent errors
are encountered or a subsequent \fBexit\fP statement with
an expression is executed.
.SS Output Statements
.LP
Both \fBprint\fP and \fBprintf\fP statements shall write to standard
output by default. The output shall be written to the
location specified by \fIoutput_redirection\fP if one is supplied,
as follows:
.sp
.RS
.nf

\fB>\fP \fIexpression\fP\fB>>\fP \fIexpression\fP\fB|\fP \fIexpression\fP
.fi
.RE
.LP
In all cases, the \fIexpression\fP shall be evaluated to produce a
string that is used as a pathname into which to write (for
\fB'>'\fP or \fB">>"\fP ) or as a command to be executed (for \fB'|'\fP
). Using the first two forms, if the file
of that name is not currently open, it shall be opened, creating it
if necessary and using the first form, truncating the file. The
output then shall be appended to the file. As long as the file remains
open, subsequent calls in which \fIexpression\fP evaluates
to the same string value shall simply append output to the file. The
file remains open until the \fBclose\fP function (see Input/Output
and General Functions ) is called with an expression that evaluates
to the same string
value.
.LP
The third form shall write output onto a stream piped to the input
of a command. The stream shall be created if no stream is
currently open with the value of \fIexpression\fP as its command name.
The stream created shall be equivalent to one created by a
call to the \fIpopen\fP() function defined in the System Interfaces
volume of
IEEE\ Std\ 1003.1-2001 with the value of \fIexpression\fP as the \fIcommand\fP
argument and a value of \fIw\fP as the
\fImode\fP argument. As long as the stream remains open, subsequent
calls in which \fIexpression\fP evaluates to the same string
value shall write output to the existing stream. The stream shall
remain open until the \fBclose\fP function (see Input/Output and General
Functions ) is called with an expression that evaluates to the same
string value.
At that time, the stream shall be closed as if by a call to the \fIpclose\fP()
function
defined in the System Interfaces volume of IEEE\ Std\ 1003.1-2001.
.LP
As described in detail by the grammar in Grammar , these output statements
shall take a
comma-separated list of \fIexpression\fPs referred to in the grammar
by the non-terminal symbols \fBexpr_list\fP,
\fBprint_expr_list\fP, or \fBprint_expr_list_opt\fP. This list is
referred to here as the \fIexpression list\fP, and each member
is referred to as an \fIexpression argument\fP.
.LP
The \fBprint\fP statement shall write the value of each expression
argument onto the indicated output stream separated by the
current output field separator (see variable \fBOFS\fP above), and
terminated by the output record separator (see variable
\fBORS\fP above). All expression arguments shall be taken as strings,
being converted if necessary; this conversion shall be as
described in Expressions in awk , with the exception that the \fBprintf\fP
format in \fBOFMT\fP
shall be used instead of the value in \fBCONVFMT\fP. An empty expression
list shall stand for the whole input record ($0).
.LP
The \fBprintf\fP statement shall produce output based on a notation
similar to the File Format Notation used to describe file
formats in this volume of IEEE\ Std\ 1003.1-2001 (see the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, Chapter 5, File Format Notation).
Output shall be produced as specified with the first
\fIexpression\fP argument as the string \fIformat\fP and subsequent
\fIexpression\fP arguments as the strings \fIarg1\fP to
\fIargn\fP, inclusive, with the following exceptions:
.IP " 1." 4
The \fIformat\fP shall be an actual character string rather than a
graphical representation. Therefore, it cannot contain empty
character positions. The <space> in the \fIformat\fP string, in any
context other than a \fIflag\fP of a conversion
specification, shall be treated as an ordinary character that is copied
to the output.
.LP
.IP " 2." 4
If the character set contains a \fB' '\fP character and that character
appears in
the \fIformat\fP string, it shall be treated as an ordinary character
that is copied to the output.
.LP
.IP " 3." 4
The \fIescape sequences\fP beginning with a backslash character shall
be treated as sequences of ordinary characters that are
copied to the output. Note that these same sequences shall be interpreted
lexically by \fIawk\fP when they appear in literal
strings, but they shall not be treated specially by the \fBprintf\fP
statement.
.LP
.IP " 4." 4
A \fIfield width\fP or \fIprecision\fP can be specified as the \fB'*'\fP
character instead of a digit string. In this case
the next argument from the expression list shall be fetched and its
numeric value taken as the field width or precision.
.LP
.IP " 5." 4
The implementation shall not precede or follow output from the \fBd\fP
or \fBu\fP conversion specifier characters with
<blank>s not specified by the \fIformat\fP string.
.LP
.IP " 6." 4
The implementation shall not precede output from the \fBo\fP conversion
specifier character with leading zeros not specified
by the \fIformat\fP string.
.LP
.IP " 7." 4
For the \fBc\fP conversion specifier character: if the argument has
a numeric value, the character whose encoding is that
value shall be output. If the value is zero or is not the encoding
of any character in the character set, the behavior is
undefined. If the argument does not have a numeric value, the first
character of the string value shall be output; if the string
does not contain any characters, the behavior is undefined.
.LP
.IP " 8." 4
For each conversion specification that consumes an argument, the next
expression argument shall be evaluated. With the exception
of the \fBc\fP conversion specifier character, the value shall be
converted (according to the rules specified in Expressions in awk
) to the appropriate type for the conversion specification.
.LP
.IP " 9." 4
If there are insufficient expression arguments to satisfy all the
conversion specifications in the \fIformat\fP string, the
behavior is undefined.
.LP
.IP "10." 4
If any character sequence in the \fIformat\fP string begins with a
\fB'%'\fP character, but does not form a valid conversion
specification, the behavior is unspecified.
.LP
.LP
Both \fBprint\fP and \fBprintf\fP can output at least {LINE_MAX} bytes.
.SS Functions
.LP
The \fIawk\fP language has a variety of built-in functions: arithmetic,
string, input/output, and general.
.SS Arithmetic Functions
.LP
The arithmetic functions, except for \fBint\fP, shall be based on
the ISO\ C standard (see \fIConcepts Derived from the ISO C Standard\fP
). The behavior is undefined in cases where the
ISO\ C standard specifies that an error be returned or that the behavior
is undefined. Although the grammar (see Grammar ) permits built-in
functions to appear with no arguments or parentheses, unless the argument
or
parentheses are indicated as optional in the following list (by displaying
them within the \fB"[]"\fP brackets), such use is
undefined.
.TP 7
\fBatan2\fP(\fIy\fP,\fIx\fP)
Return arctangent of \fIy\fP/\fIx\fP in radians in the range [-pi,pi].
.TP 7
\fBcos\fP(\fIx\fP)
Return cosine of \fIx\fP, where \fIx\fP is in radians.
.TP 7
\fBsin\fP(\fIx\fP)
Return sine of \fIx\fP, where \fIx\fP is in radians.
.TP 7
\fBexp\fP(\fIx\fP)
Return the exponential function of \fIx\fP.
.TP 7
\fBlog\fP(\fIx\fP)
Return the natural logarithm of \fIx\fP.
.TP 7
\fBsqrt\fP(\fIx\fP)
Return the square root of \fIx\fP.
.TP 7
\fBint\fP(\fIx\fP)
Return the argument truncated to an integer. Truncation shall be toward
0 when \fIx\fP>0.
.TP 7
\fBrand\fP()
Return a random number \fIn\fP, such that 0<=\fIn\fP<1.
.TP 7
\fBsrand\fP(\fB[\fP\fIexpr\fP\fB]\fP)
Set the seed value for \fIrand\fP to \fIexpr\fP or use the time of
day if \fIexpr\fP is omitted. The previous seed value
shall be returned.
.sp
.SS String Functions
.LP
The string functions in the following list shall be supported. Although
the grammar (see Grammar
) permits built-in functions to appear with no arguments or parentheses,
unless the argument or parentheses are indicated as
optional in the following list (by displaying them within the \fB"[]"\fP
brackets), such use is undefined.
.TP 7
\fBgsub\fP(\fIere\fP,\ \fIrepl\fP\fB[\fP,\ \fIin\fP\fB]\fP)
Behave like \fBsub\fP (see below), except that it shall replace all
occurrences of the regular expression (like the \fIed\fP utility global
substitute) in $0 or in the \fIin\fP argument, when specified.
.TP 7
\fBindex\fP(\fIs\fP,\ \fIt\fP)
Return the position, in characters, numbering from 1, in string \fIs\fP
where string \fIt\fP first occurs, or zero if it does
not occur at all.
.TP 7
\fBlength[\fP(\fB[\fP\fIs\fP\fB]\fP)\fB]\fP
Return the length, in characters, of its argument taken as a string,
or of the whole record, $0, if there is no argument.
.TP 7
\fBmatch\fP(\fIs\fP,\ \fIere\fP)
Return the position, in characters, numbering from 1, in string \fIs\fP
where the extended regular expression \fIere\fP
occurs, or zero if it does not occur at all. RSTART shall be set to
the starting position (which is the same as the returned
value), zero if no match is found; RLENGTH shall be set to the length
of the matched string, -1 if no match is found.
.TP 7
\fBsplit\fP(\fIs\fP,\ \fIa\fP\fB[\fP,\ \fIfs\ \fP \fB]\fP)
Split the string \fIs\fP into array elements \fIa\fP[1], \fIa\fP[2],
\&..., \fIa\fP[\fIn\fP], and return \fIn\fP. All elements
of the array shall be deleted before the split is performed. The separation
shall be done with the ERE \fIfs\fP or with the field
separator \fBFS\fP if \fIfs\fP is not given. Each array element shall
have a string value when created and, if appropriate, the
array element shall be considered a numeric string (see Expressions
in awk ). The effect of a null
string as the value of \fIfs\fP is unspecified.
.TP 7
\fBsprintf\fP(\fIfmt\fP,\ \fIexpr\fP,\ \fIexpr\fP,\ ...)
Format the expressions according to the \fBprintf\fP format given
by \fIfmt\fP and return the resulting string.
.TP 7
\fBsub(\fP\fIere\fP,\ \fIrepl\fP\fB[\fP,\ \fIin\ \fP \fB]\fP)
Substitute the string \fIrepl\fP in place of the first instance of
the extended regular expression \fIERE\fP in string \fIin\fP
and return the number of substitutions. An ampersand ( \fB'&'\fP )
appearing in the string \fIrepl\fP shall be replaced by
the string from \fIin\fP that matches the ERE. An ampersand preceded
with a backslash ( \fB'\\'\fP ) shall be interpreted as the
literal ampersand character. An occurrence of two consecutive backslashes
shall be interpreted as just a single literal backslash
character. Any other occurrence of a backslash (for example, preceding
any other character) shall be treated as a literal backslash
character. Note that if \fIrepl\fP is a string literal (the lexical
token \fBSTRING\fP; see Grammar ), the handling of the ampersand character
occurs after any lexical processing, including any
lexical backslash escape sequence processing. If \fIin\fP is specified
and it is not an lvalue (see Expressions in awk ), the behavior is
undefined. If \fIin\fP is omitted, \fIawk\fP shall use the current
record ($0) in its place.
.TP 7
\fBsubstr\fP(\fIs\fP,\ \fIm\fP\fB[\fP,\ \fIn\ \fP \fB]\fP)
Return the at most \fIn\fP-character substring of \fIs\fP that begins
at position \fIm\fP, numbering from 1. If \fIn\fP is
omitted, or if \fIn\fP specifies more characters than are left in
the string, the length of the substring shall be limited by the
length of the string \fIs\fP.
.TP 7
\fBtolower\fP(\fIs\fP)
Return a string based on the string \fIs\fP. Each character in \fIs\fP
that is an uppercase letter specified to have a
\fBtolower\fP mapping by the \fILC_CTYPE\fP category of the current
locale shall be replaced in the returned string by the
lowercase letter specified by the mapping. Other characters in \fIs\fP
shall be unchanged in the returned string.
.TP 7
\fBtoupper\fP(\fIs\fP)
Return a string based on the string \fIs\fP. Each character in \fIs\fP
that is a lowercase letter specified to have a
\fBtoupper\fP mapping by the \fILC_CTYPE\fP category of the current
locale is replaced in the returned string by the uppercase
letter specified by the mapping. Other characters in \fIs\fP are unchanged
in the returned string.
.sp
.LP
All of the preceding functions that take \fIERE\fP as a parameter
expect a pattern or a string valued expression that is a
regular expression as defined in Regular Expressions .
.SS Input/Output and General Functions
.LP
The input/output and general functions are:
.TP 7
\fBclose\fP(\fIexpression\fP)
Close the file or pipe opened by a \fBprint\fP or \fBprintf\fP statement
or a call to \fBgetline\fP with the same string-valued
\fIexpression\fP. The limit on the number of open \fIexpression\fP
arguments is implementation-defined. If the close was
successful, the function shall return zero; otherwise, it shall return
non-zero.
.TP 7
\fIexpression\ |\ \fP \fBgetline\ [\fP\fIvar\fP\fB]\fP
Read a record of input from a stream piped from the output of a command.
The stream shall be created if no stream is currently open
with the value of \fIexpression\fP as its command name. The stream
created shall be equivalent to one created by a call to the \fIpopen\fP()
function with the value of \fIexpression\fP as the \fIcommand\fP argument
and a
value of \fIr\fP as the \fImode\fP argument. As long as the stream
remains open, subsequent calls in which \fIexpression\fP
evaluates to the same string value shall read subsequent records from
the stream. The stream shall remain open until the
\fBclose\fP function is called with an expression that evaluates to
the same string value. At that time, the stream shall be
closed as if by a call to the \fIpclose\fP() function. If \fIvar\fP
is omitted, $0 and
\fBNF\fP shall be set; otherwise, \fIvar\fP shall be set and, if appropriate,
it shall be considered a numeric string (see Expressions in awk ).
.LP
The \fBgetline\fP operator can form ambiguous constructs when there
are unparenthesized operators (including concatenate) to
the left of the \fB'|'\fP (to the beginning of the expression containing
\fBgetline\fP). In the context of the \fB'$'\fP
operator, \fB'|'\fP shall behave as if it had a lower precedence than
\fB'$'\fP . The result of evaluating other operators is
unspecified, and conforming applications shall parenthesize properly
all such usages.
.TP 7
\fBgetline\fP
Set $0 to the next input record from the current input file. This
form of \fBgetline\fP shall set the \fBNF\fP, \fBNR\fP,
and \fBFNR\fP variables.
.TP 7
\fBgetline\ \fP \fIvar\fP
Set variable \fIvar\fP to the next input record from the current input
file and, if appropriate, \fIvar\fP shall be
considered a numeric string (see Expressions in awk ). This form of
\fBgetline\fP shall set the
\fBFNR\fP and \fBNR\fP variables.
.TP 7
\fBgetline\ [\fP\fIvar\fP\fB]\ \fP <\ \fIexpression\fP
Read the next record of input from a named file. The \fIexpression\fP
shall be evaluated to produce a string that is used as a
pathname. If the file of that name is not currently open, it shall
be opened. As long as the stream remains open, subsequent calls
in which \fIexpression\fP evaluates to the same string value shall
read subsequent records from the file. The file shall remain
open until the \fBclose\fP function is called with an expression that
evaluates to the same string value. If \fIvar\fP is
omitted, $0 and \fBNF\fP shall be set; otherwise, \fIvar\fP shall
be set and, if appropriate, it shall be considered a numeric
string (see Expressions in awk ). 
.LP
The \fBgetline\fP operator can form ambiguous constructs when there
are unparenthesized binary operators (including
concatenate) to the right of the \fB'<'\fP (up to the end of the expression
containing the \fBgetline\fP). The result of
evaluating such a construct is unspecified, and conforming applications
shall parenthesize properly all such usages.
.TP 7
\fBsystem\fP(\fIexpression\fP)
Execute the command given by \fIexpression\fP in a manner equivalent
to the \fIsystem\fP()
function defined in the System Interfaces volume of IEEE\ Std\ 1003.1-2001
and return the exit status of the command.
.sp
.LP
All forms of \fBgetline\fP shall return 1 for successful input, zero
for end-of-file, and -1 for an error.
.LP
Where strings are used as the name of a file or pipeline, the application
shall ensure that the strings are textually identical.
The terminology "same string value" implies that "equivalent strings",
even those that differ only by <space>s, represent
different files.
.SS User-Defined Functions
.LP
The \fIawk\fP language also provides user-defined functions. Such
functions can be defined as:
.sp
.RS
.nf

\fBfunction\fP \fIname\fP\fB(\fP\fB[\fP\fIparameter\fP\fB, ...\fP\fB]\fP\fB) {\fP \fIstatements\fP \fB}
\fP
.fi
.RE
.LP
A function can be referred to anywhere in an \fIawk\fP program; in
particular, its use can precede its definition. The scope of
a function is global.
.LP
Function parameters, if present, can be either scalars or arrays;
the behavior is undefined if an array name is passed as a
parameter that the function uses as a scalar, or if a scalar expression
is passed as a parameter that the function uses as an
array. Function parameters shall be passed by value if scalar and
by reference if array name.
.LP
The number of parameters in the function definition need not match
the number of parameters in the function call. Excess formal
parameters can be used as local variables. If fewer arguments are
supplied in a function call than are in the function definition,
the extra parameters that are used in the function body as scalars
shall evaluate to the uninitialized value until they are
otherwise initialized, and the extra parameters that are used in the
function body as arrays shall be treated as uninitialized
arrays where each element evaluates to the uninitialized value until
otherwise initialized.
.LP
When invoking a function, no white space can be placed between the
function name and the opening parenthesis. Function calls can
be nested and recursive calls can be made upon functions. Upon return
from any nested or recursive function call, the values of all
of the calling function's parameters shall be unchanged, except for
array parameters passed by reference. The \fBreturn\fP
statement can be used to return a value. If a \fBreturn\fP statement
appears outside of a function definition, the behavior is
undefined.
.LP
In the function definition, <newline>s shall be optional before the
opening brace and after the closing brace. Function
definitions can appear anywhere in the program where a \fIpattern-action\fP
pair is allowed.
.SS Grammar
.LP
The grammar in this section and the lexical conventions in the following
section shall together describe the syntax for
\fIawk\fP programs. The general conventions for this style of grammar
are described in \fIGrammar Conventions\fP . A valid program can be
represented as the non-terminal symbol
\fIprogram\fP in the grammar. This formal syntax shall take precedence
over the preceding text syntax description.
.sp
.RS
.nf

\fB%token NAME NUMBER STRING ERE
%token FUNC_NAME   /* Name followed by '(' without white space. */
.sp

/* Keywords  */
%token       Begin   End
/*          'BEGIN' 'END'                            */
.sp

%token       Break   Continue   Delete   Do   Else
/*          'break' 'continue' 'delete' 'do' 'else'  */
.sp

%token       Exit   For   Function   If   In
/*          'exit' 'for' 'function' 'if' 'in'        */
.sp

%token       Next   Print   Printf   Return   While
/*          'next' 'print' 'printf' 'return' 'while' */
.sp

/* Reserved function names */
%token BUILTIN_FUNC_NAME
            /* One token for the following:
             * atan2 cos sin exp log sqrt int rand srand
             * gsub index length match split sprintf sub
             * substr tolower toupper close system
             */
%token GETLINE
            /* Syntactically different from other built-ins. */
.sp

/* Two-character tokens. */
%token ADD_ASSIGN SUB_ASSIGN MUL_ASSIGN DIV_ASSIGN MOD_ASSIGN POW_ASSIGN
/*     '+='       '-='       '*='       '/='       '%='       '^=' */
.sp

%token OR   AND  NO_MATCH   EQ   LE   GE   NE   INCR  DECR  APPEND
/*     '||' '&&' '!~' '==' '<=' '>=' '!=' '++'  '--'  '>>'   */
.sp

/* One-character tokens. */
%token '{' '}' '(' ')' '[' ']' ',' ';' NEWLINE
%token '+' '-' '*' '%' '^' '!' '>' '<' '|' '?' ':' '~' '$' '='
.sp

%start program
%%
.sp

program          : item_list
                 | actionless_item_list
                 ;
.sp

item_list        : newline_opt
                 | actionless_item_list item terminator
                 | item_list            item terminator
                 | item_list          action terminator
                 ;
.sp

actionless_item_list : item_list            pattern terminator
                 | actionless_item_list pattern terminator
                 ;
.sp

item             : pattern action
                 | Function NAME      '(' param_list_opt ')'
                       newline_opt action
                 | Function FUNC_NAME '(' param_list_opt ')'
                       newline_opt action
                 ;
.sp

param_list_opt   : /* empty */
                 | param_list
                 ;
.sp

param_list       : NAME
                 | param_list ',' NAME
                 ;
.sp

pattern          : Begin
                 | End
                 | expr
                 | expr ',' newline_opt expr
                 ;
.sp

action           : '{' newline_opt                             '}'
                 | '{' newline_opt terminated_statement_list   '}'
                 | '{' newline_opt unterminated_statement_list '}'
                 ;
.sp

terminator       : terminator ';'
                 | terminator NEWLINE
                 |            ';'
                 |            NEWLINE
                 ;
.sp

terminated_statement_list : terminated_statement
                 | terminated_statement_list terminated_statement
                 ;
.sp

unterminated_statement_list : unterminated_statement
                 | terminated_statement_list unterminated_statement
                 ;
.sp

terminated_statement : action newline_opt
                 | If '(' expr ')' newline_opt terminated_statement
                 | If '(' expr ')' newline_opt terminated_statement
                       Else newline_opt terminated_statement
                 | While '(' expr ')' newline_opt terminated_statement
                 | For '(' simple_statement_opt ';'
                      expr_opt ';' simple_statement_opt ')' newline_opt
                      terminated_statement
                 | For '(' NAME In NAME ')' newline_opt
                      terminated_statement
                 | ';' newline_opt
                 | terminatable_statement NEWLINE newline_opt
                 | terminatable_statement ';'     newline_opt
                 ;
.sp

unterminated_statement : terminatable_statement
                 | If '(' expr ')' newline_opt unterminated_statement
                 | If '(' expr ')' newline_opt terminated_statement
                      Else newline_opt unterminated_statement
                 | While '(' expr ')' newline_opt unterminated_statement
                 | For '(' simple_statement_opt ';'
                  expr_opt ';' simple_statement_opt ')' newline_opt
                      unterminated_statement
                 | For '(' NAME In NAME ')' newline_opt
                      unterminated_statement
                 ;
.sp

terminatable_statement : simple_statement
                 | Break
                 | Continue
                 | Next
                 | Exit expr_opt
                 | Return expr_opt
                 | Do newline_opt terminated_statement While '(' expr ')'
                 ;
.sp

simple_statement_opt : /* empty */
                 | simple_statement
                 ;
.sp

simple_statement : Delete NAME '[' expr_list ']'
                 | expr
                 | print_statement
                 ;
.sp

print_statement  : simple_print_statement
                 | simple_print_statement output_redirection
                 ;
.sp

simple_print_statement : Print  print_expr_list_opt
                 | Print  '(' multiple_expr_list ')'
                 | Printf print_expr_list
                 | Printf '(' multiple_expr_list ')'
                 ;
.sp

output_redirection : '>'    expr
                 | APPEND expr
                 | '|'    expr
                 ;
.sp

expr_list_opt    : /* empty */
                 | expr_list
                 ;
.sp

expr_list        : expr
                 | multiple_expr_list
                 ;
.sp

multiple_expr_list : expr ',' newline_opt expr
                 | multiple_expr_list ',' newline_opt expr
                 ;
.sp

expr_opt         : /* empty */
                 | expr
                 ;
.sp

expr             : unary_expr
                 | non_unary_expr
                 ;
.sp

unary_expr       : '+' expr
                 | '-' expr
                 | unary_expr '^'      expr
                 | unary_expr '*'      expr
                 | unary_expr '/'      expr
                 | unary_expr '%'      expr
                 | unary_expr '+'      expr
                 | unary_expr '-'      expr
                 | unary_expr          non_unary_expr
                 | unary_expr '<'      expr
                 | unary_expr LE       expr
                 | unary_expr NE       expr
                 | unary_expr EQ       expr
                 | unary_expr '>'      expr
                 | unary_expr GE       expr
                 | unary_expr '~'      expr
                 | unary_expr NO_MATCH expr
                 | unary_expr In NAME
                 | unary_expr AND newline_opt expr
                 | unary_expr OR  newline_opt expr
                 | unary_expr '?' expr ':' expr
                 | unary_input_function
                 ;
.sp

non_unary_expr   : '(' expr ')'
                 | '!' expr
                 | non_unary_expr '^'      expr
                 | non_unary_expr '*'      expr
                 | non_unary_expr '/'      expr
                 | non_unary_expr '%'      expr
                 | non_unary_expr '+'      expr
                 | non_unary_expr '-'      expr
                 | non_unary_expr          non_unary_expr
                 | non_unary_expr '<'      expr
                 | non_unary_expr LE       expr
                 | non_unary_expr NE       expr
                 | non_unary_expr EQ       expr
                 | non_unary_expr '>'      expr
                 | non_unary_expr GE       expr
                 | non_unary_expr '~'      expr
                 | non_unary_expr NO_MATCH expr
                 | non_unary_expr In NAME
                 | '(' multiple_expr_list ')' In NAME
                 | non_unary_expr AND newline_opt expr
                 | non_unary_expr OR  newline_opt expr
                 | non_unary_expr '?' expr ':' expr
                 | NUMBER
                 | STRING
                 | lvalue
                 | ERE
                 | lvalue INCR
                 | lvalue DECR
                 | INCR lvalue
                 | DECR lvalue
                 | lvalue POW_ASSIGN expr
                 | lvalue MOD_ASSIGN expr
                 | lvalue MUL_ASSIGN expr
                 | lvalue DIV_ASSIGN expr
                 | lvalue ADD_ASSIGN expr
                 | lvalue SUB_ASSIGN expr
                 | lvalue '=' expr
                 | FUNC_NAME '(' expr_list_opt ')'
                      /* no white space allowed before '(' */
                 | BUILTIN_FUNC_NAME '(' expr_list_opt ')'
                 | BUILTIN_FUNC_NAME
                 | non_unary_input_function
                 ;
.sp

print_expr_list_opt : /* empty */
                 | print_expr_list
                 ;
.sp

print_expr_list  : print_expr
                 | print_expr_list ',' newline_opt print_expr
                 ;
.sp

print_expr       : unary_print_expr
                 | non_unary_print_expr
                 ;
.sp

unary_print_expr : '+' print_expr
                 | '-' print_expr
                 | unary_print_expr '^'      print_expr
                 | unary_print_expr '*'      print_expr
                 | unary_print_expr '/'      print_expr
                 | unary_print_expr '%'      print_expr
                 | unary_print_expr '+'      print_expr
                 | unary_print_expr '-'      print_expr
                 | unary_print_expr          non_unary_print_expr
                 | unary_print_expr '~'      print_expr
                 | unary_print_expr NO_MATCH print_expr
                 | unary_print_expr In NAME
                 | unary_print_expr AND newline_opt print_expr
                 | unary_print_expr OR  newline_opt print_expr
                 | unary_print_expr '?' print_expr ':' print_expr
                 ;
.sp

non_unary_print_expr : '(' expr ')'
                 | '!' print_expr
                 | non_unary_print_expr '^'      print_expr
                 | non_unary_print_expr '*'      print_expr
                 | non_unary_print_expr '/'      print_expr
                 | non_unary_print_expr '%'      print_expr
                 | non_unary_print_expr '+'      print_expr
                 | non_unary_print_expr '-'      print_expr
                 | non_unary_print_expr          non_unary_print_expr
                 | non_unary_print_expr '~'      print_expr
                 | non_unary_print_expr NO_MATCH print_expr
                 | non_unary_print_expr In NAME
                 | '(' multiple_expr_list ')' In NAME
                 | non_unary_print_expr AND newline_opt print_expr
                 | non_unary_print_expr OR  newline_opt print_expr
                 | non_unary_print_expr '?' print_expr ':' print_expr
                 | NUMBER
                 | STRING
                 | lvalue
                 | ERE
                 | lvalue INCR
                 | lvalue DECR
                 | INCR lvalue
                 | DECR lvalue
                 | lvalue POW_ASSIGN print_expr
                 | lvalue MOD_ASSIGN print_expr
                 | lvalue MUL_ASSIGN print_expr
                 | lvalue DIV_ASSIGN print_expr
                 | lvalue ADD_ASSIGN print_expr
                 | lvalue SUB_ASSIGN print_expr
                 | lvalue '=' print_expr
                 | FUNC_NAME '(' expr_list_opt ')'
                     /* no white space allowed before '(' */
                 | BUILTIN_FUNC_NAME '(' expr_list_opt ')'
                 | BUILTIN_FUNC_NAME
                 ;
.sp

lvalue           : NAME
                 | NAME '[' expr_list ']'
                 | '$' expr
                 ;
.sp

non_unary_input_function : simple_get
                 | simple_get '<' expr
                 | non_unary_expr '|' simple_get
                 ;
.sp

unary_input_function : unary_expr '|' simple_get
                 ;
.sp

simple_get       : GETLINE
                 | GETLINE lvalue
                 ;
.sp

newline_opt      : /* empty */
                 | newline_opt NEWLINE
                 ;
\fP
.fi
.RE
.LP
This grammar has several ambiguities that shall be resolved as follows:
.IP " *" 3
Operator precedence and associativity shall be as described in Expressions
in Decreasing Precedence in \fIawk\fP .
.LP
.IP " *" 3
In case of ambiguity, an \fBelse\fP shall be associated with the most
immediately preceding \fBif\fP that would satisfy the
grammar.
.LP
.IP " *" 3
In some contexts, a slash ( \fB'/'\fP ) that is used to surround an
ERE could also be the division operator. This shall be
resolved in such a way that wherever the division operator could appear,
a slash is assumed to be the division operator. (There is
no unary division operator.)
.LP
.LP
One convention that might not be obvious from the formal grammar is
where <newline>s are acceptable. There are several
obvious placements such as terminating a statement, and a backslash
can be used to escape <newline>s between any lexical
tokens. In addition, <newline>s without backslashes can follow a comma,
an open brace, logical AND operator (
\fB"&&"\fP ), logical OR operator ( \fB"||"\fP ), the \fBdo\fP keyword,
the \fBelse\fP keyword, and the closing
parenthesis of an \fBif\fP, \fBfor\fP, or \fBwhile\fP statement. For
example:
.sp
.RS
.nf

\fB{ print  $1,
         $2 }
\fP
.fi
.RE
.SS Lexical Conventions
.LP
The lexical conventions for \fIawk\fP programs, with respect to the
preceding grammar, shall be as follows:
.IP " 1." 4
Except as noted, \fIawk\fP shall recognize the longest possible token
or delimiter beginning at a given point.
.LP
.IP " 2." 4
A comment shall consist of any characters beginning with the number
sign character and terminated by, but excluding the next
occurrence of, a <newline>. Comments shall have no effect, except
to delimit lexical tokens.
.LP
.IP " 3." 4
The <newline> shall be recognized as the token \fBNEWLINE\fP.
.LP
.IP " 4." 4
A backslash character immediately followed by a <newline> shall have
no effect.
.LP
.IP " 5." 4
The token \fBSTRING\fP shall represent a string constant. A string
constant shall begin with the character \fB' .'\fP Within
a string constant, a backslash character shall be considered to begin
an escape sequence as specified in the table in the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter 5, File Format
Notation (
\fB'\\\\'\fP, \fB'\\a'\fP, \fB'\\b'\fP, \fB'\\f'\fP, \fB'\\n'\fP,
\fB'\\r'\fP, \fB'\\t'\fP, \fB'\\v'\fP ). In
addition, the escape sequences in Expressions in Decreasing Precedence
in \fIawk\fP shall be recognized. A <newline> shall not
occur within a string constant. A string constant shall be terminated
by the first unescaped occurrence of the character
\fB''\fP after the one that begins the string constant. The value
of the string shall be the sequence of all unescaped
characters and values of escape sequences between, but not including,
the two delimiting \fB''\fP characters.
.LP
.IP " 6." 4
The token \fBERE\fP represents an extended regular expression constant.
An ERE constant shall begin with the slash character.
Within an ERE constant, a backslash character shall be considered
to begin an escape sequence as specified in the table in the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter 5, File Format
Notation. In
addition, the escape sequences in Expressions in Decreasing Precedence
in \fIawk\fP shall be recognized. The application shall
ensure that a <newline> does not occur within an ERE constant. An
ERE constant shall be terminated by the first unescaped
occurrence of the slash character after the one that begins the ERE
constant. The extended regular expression represented by the
ERE constant shall be the sequence of all unescaped characters and
values of escape sequences between, but not including, the two
delimiting slash characters.
.LP
.IP " 7." 4
A <blank> shall have no effect, except to delimit lexical tokens or
within \fBSTRING\fP or \fBERE\fP tokens.
.LP
.IP " 8." 4
The token \fBNUMBER\fP shall represent a numeric constant. Its form
and numeric value shall be equivalent to either of the
tokens \fBfloating-constant\fP or \fBinteger-constant\fP as specified
by the ISO\ C standard, with the following
exceptions:
.RS
.IP " a." 4
An integer constant cannot begin with 0x or include the hexadecimal
digits \fB'a'\fP, \fB'b'\fP, \fB'c'\fP,
\fB'd'\fP, \fB'e'\fP, \fB'f'\fP, \fB'A'\fP, \fB'B'\fP, \fB'C'\fP,
\fB'D'\fP, \fB'E'\fP, or
\fB'F'\fP .
.LP
.IP " b." 4
The value of an integer constant beginning with 0 shall be taken in
decimal rather than octal.
.LP
.IP " c." 4
An integer constant cannot include a suffix ( \fB'u'\fP, \fB'U'\fP,
\fB'l'\fP, or \fB'L'\fP ).
.LP
.IP " d." 4
A floating constant cannot include a suffix ( \fB'f'\fP, \fB'F'\fP,
\fB'l'\fP, or \fB'L'\fP ).
.LP
.RE
.LP
If the value is too large or too small to be representable (see \fIConcepts
Derived from
the ISO C Standard\fP ), the behavior is undefined.
.LP
.IP " 9." 4
A sequence of underscores, digits, and alphabetics from the portable
character set (see the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 6.1, Portable Character Set), beginning
with an underscore or alphabetic, shall be considered a word.
.LP
.IP "10." 4
The following words are keywords that shall be recognized as individual
tokens; the name of the token is the same as the
keyword:
.TS C
center; lw(13) lw(13) lw(13) lw(13) lw(13) lw(13).
T{
\fB
.br
BEGIN
.br
break
.br
continue
.br
\fP
T}	T{
\fB
.br
delete
.br
do
.br
else
.br
\fP
T}	T{
\fB
.br
END
.br
exit
.br
for
.br
\fP
T}	T{
\fB
.br
function
.br
getline
.br
if
.br
\fP
T}	T{
\fB
.br
in
.br
next
.br
print
.br
\fP
T}	T{
\fB
.br
printf
.br
return
.br
while
.br
\fP
T}
.TE
.LP
.IP "11." 4
The following words are names of built-in functions and shall be recognized
as the token \fBBUILTIN_FUNC_NAME\fP:
.TS C
center; lw(13) lw(13) lw(13) lw(13) lw(13) lw(13).
T{
\fB
.br
atan2
.br
close
.br
cos
.br
exp
.br
\fP
T}	T{
\fB
.br
gsub
.br
index
.br
int
.br
length
.br
\fP
T}	T{
\fB
.br
log
.br
match
.br
rand
.br
sin
.br
\fP
T}	T{
\fB
.br
split
.br
sprintf
.br
sqrt
.br
srand
.br
\fP
T}	T{
\fB
.br
sub
.br
substr
.br
system
.br
tolower
.br
\fP
T}	T{
\fB
.br
toupper
.br
\fP
T}
.TE
.LP
The above-listed keywords and names of built-in functions are considered
reserved words.
.LP
.IP "12." 4
The token \fBNAME\fP shall consist of a word that is not a keyword
or a name of a built-in function and is not followed
immediately (without any delimiters) by the \fB'('\fP character.
.LP
.IP "13." 4
The token \fBFUNC_NAME\fP shall consist of a word that is not a keyword
or a name of a built-in function, followed immediately
(without any delimiters) by the \fB'('\fP character. The \fB'('\fP
character shall not be included as part of the token.
.LP
.IP "14." 4
The following two-character sequences shall be recognized as the named
tokens:
.TS C
center; l l l l.
\fBToken Name\fP	\fBSequence\fP	\fBToken Name\fP	\fBSequence\fP
\fBADD_ASSIGN\fP	+=	\fBNO_MATCH\fP	!~
\fBSUB_ASSIGN\fP	-=	\fBEQ\fP	==
\fBMUL_ASSIGN\fP	*=	\fBLE\fP	<=
\fBDIV_ASSIGN\fP	/=	\fBGE\fP	>=
\fBMOD_ASSIGN\fP	%=	\fBNE\fP	!=
\fBPOW_ASSIGN\fP	^=	\fBINCR\fP	++
\fBOR\fP	||	\fBDECR\fP	--
\fBAND\fP	&&	\fBAPPEND\fP	>>
.TE
.LP
.IP "15." 4
The following single characters shall be recognized as tokens whose
names are the character:
.sp
.RS
.nf

\fB<newline> { } ( ) [ ] , ; + - * % ^ ! > < | ? : ~ $ =
\fP
.fi
.RE
.LP
.LP
There is a lexical ambiguity between the token \fBERE\fP and the tokens
\fB'/'\fP and \fBDIV_ASSIGN\fP. When an input
sequence begins with a slash character in any syntactic context where
the token \fB'/'\fP or \fBDIV_ASSIGN\fP could appear as
the next token in a valid program, the longer of those two tokens
that can be recognized shall be recognized. In any other
syntactic context where the token \fBERE\fP could appear as the next
token in a valid program, the token \fBERE\fP shall be
recognized.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
All input files were processed successfully.
.TP 7
>0
An error occurred.
.sp
.LP
The exit status can be altered within the program by using an \fBexit\fP
expression.
.SH CONSEQUENCES OF ERRORS
.LP
If any \fIfile\fP operand is specified and the named file cannot be
accessed, \fIawk\fP shall write a diagnostic message to
standard error and terminate without any further action.
.LP
If the program specified by either the \fIprogram\fP operand or a
\fIprogfile\fP operand is not a valid \fIawk\fP program (as
specified in the EXTENDED DESCRIPTION section), the behavior is undefined.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The \fBindex\fP, \fBlength\fP, \fBmatch\fP, and \fBsubstr\fP functions
should not be confused with similar functions in the
ISO\ C standard; the \fIawk\fP versions deal with characters, while
the ISO\ C standard deals with bytes.
.LP
Because the concatenation operation is represented by adjacent expressions
rather than an explicit operator, it is often
necessary to use parentheses to enforce the proper evaluation precedence.
.SH EXAMPLES
.LP
The \fIawk\fP program specified in the command line is most easily
specified within single-quotes (for example,
'\fIprogram\fP') for applications using \fIsh\fP, because \fIawk\fP
programs commonly contain
characters that are special to the shell, including double-quotes.
In the cases where an \fIawk\fP program contains single-quote
characters, it is usually easiest to specify most of the program as
strings within single-quotes concatenated by the shell with
quoted single-quote characters. For example:
.sp
.RS
.nf

\fBawk '/'\\''/ { print "quote:", $0 }'
\fP
.fi
.RE
.LP
prints all lines from the standard input containing a single-quote
character, prefixed with \fIquote\fP:.
.LP
The following are examples of simple \fIawk\fP programs:
.IP " 1." 4
Write to the standard output all input lines for which field 3 is
greater than 5:
.sp
.RS
.nf

\fB$3 > 5
\fP
.fi
.RE
.LP
.IP " 2." 4
Write every tenth line:
.sp
.RS
.nf

\fB(NR % 10) == 0
\fP
.fi
.RE
.LP
.IP " 3." 4
Write any line with a substring matching the regular expression:
.sp
.RS
.nf

\fB/(G|D)(2[0-9][[:alpha:]]*)/
\fP
.fi
.RE
.LP
.IP " 4." 4
Print any line with a substring containing a \fB'G'\fP or \fB'D'\fP,
followed by a sequence of digits and characters.
This example uses character classes \fBdigit\fP and \fBalpha\fP to
match language-independent digit and alphabetic characters
respectively:
.sp
.RS
.nf

\fB/(G|D)([[:digit:][:alpha:]]*)/
\fP
.fi
.RE
.LP
.IP " 5." 4
Write any line in which the second field matches the regular expression
and the fourth field does not:
.sp
.RS
.nf

\fB$2 ~ /xyz/ && $4 !~ /xyz/
\fP
.fi
.RE
.LP
.IP " 6." 4
Write any line in which the second field contains a backslash:
.sp
.RS
.nf

\fB$2 ~ /\\\\/
\fP
.fi
.RE
.LP
.IP " 7." 4
Write any line in which the second field contains a backslash. Note
that backslash escapes are interpreted twice; once in
lexical processing of the string and once in processing the regular
expression:
.sp
.RS
.nf

\fB$2 ~ "\\\\\\\\"
\fP
.fi
.RE
.LP
.IP " 8." 4
Write the second to the last and the last field in each line. Separate
the fields by a colon:
.sp
.RS
.nf

\fB{OFS=":";print $(NF-1), $NF}
\fP
.fi
.RE
.LP
.IP " 9." 4
Write the line number and number of fields in each line. The three
strings representing the line number, the colon, and the
number of fields are concatenated and that string is written to standard
output:
.sp
.RS
.nf

\fB{print NR ":" NF}
\fP
.fi
.RE
.LP
.IP "10." 4
Write lines longer than 72 characters:
.sp
.RS
.nf

\fBlength($0) > 72
\fP
.fi
.RE
.LP
.IP "11." 4
Write the first two fields in opposite order separated by \fBOFS\fP:
.sp
.RS
.nf

\fB{ print $2, $1 }
\fP
.fi
.RE
.LP
.IP "12." 4
Same, with input fields separated by a comma or <space>s and <tab>s,
or both:
.sp
.RS
.nf

\fBBEGIN { FS = ",[ \\t]*|[ \\t]+" }
      { print $2, $1 }
\fP
.fi
.RE
.LP
.IP "13." 4
Add up the first column, print sum, and average:
.sp
.RS
.nf

\fB     {s += $1 }
END   {print "sum is ", s, " average is", s/NR}
\fP
.fi
.RE
.LP
.IP "14." 4
Write fields in reverse order, one per line (many lines out for each
line in):
.sp
.RS
.nf

\fB{ for (i = NF; i > 0; --i) print $i }
\fP
.fi
.RE
.LP
.IP "15." 4
Write all lines between occurrences of the strings \fBstart\fP and
\fBstop\fP:
.sp
.RS
.nf

\fB/start/, /stop/
\fP
.fi
.RE
.LP
.IP "16." 4
Write all lines whose first field is different from the previous one:
.sp
.RS
.nf

\fB$1 != prev { print; prev = $1 }
\fP
.fi
.RE
.LP
.IP "17." 4
Simulate \fIecho\fP:
.sp
.RS
.nf

\fBBEGIN  {
        for (i = 1; i < ARGC; ++i)
        printf("%s%s", ARGV[i], i==ARGC-1?"\\n":" ")
}
\fP
.fi
.RE
.LP
.IP "18." 4
Write the path prefixes contained in the \fIPATH\fP environment variable,
one per line:
.sp
.RS
.nf

\fBBEGIN  {
        n = split (ENVIRON["PATH"], path, ":")
        for (i = 1; i <= n; ++i)
        print path[i]
}
\fP
.fi
.RE
.LP
.IP "19." 4
If there is a file named \fBinput\fP containing page headers of the
form:
.sp
.RS
.nf

Page #
.fi
.RE
.LP
and a file named \fBprogram\fP that contains:
.sp
.RS
.nf

\fB/Page/   { $2 = n++; }
         { print }
\fP
.fi
.RE
.LP
then the command line:
.sp
.RS
.nf

\fBawk -f program n=5 input
\fP
.fi
.RE
.LP
prints the file \fBinput\fP, filling in page numbers starting at 5.
.LP
.SH RATIONALE
.LP
This description is based on the new \fIawk\fP, "nawk", (see the referenced
\fIThe AWK Programming Language\fP), which
introduced a number of new features to the historical \fIawk\fP:
.IP " 1." 4
New keywords: \fBdelete\fP, \fBdo\fP, \fBfunction\fP, \fBreturn\fP
.LP
.IP " 2." 4
New built-in functions: \fBatan2\fP, \fBclose\fP, \fBcos\fP, \fBgsub\fP,
\fBmatch\fP, \fBrand\fP, \fBsin\fP,
\fBsrand\fP, \fBsub\fP, \fBsystem\fP
.LP
.IP " 3." 4
New predefined variables: \fBFNR\fP, \fBARGC\fP, \fBARGV\fP, \fBRSTART\fP,
\fBRLENGTH\fP, \fBSUBSEP\fP
.LP
.IP " 4." 4
New expression operators: \fB?\fP, \fB:\fP, \fB,\fP, \fB^\fP
.LP
.IP " 5." 4
The \fBFS\fP variable and the third argument to \fBsplit\fP, now treated
as extended regular expressions.
.LP
.IP " 6." 4
The operator precedence, changed to more closely match the C language.
Two examples of code that operate differently are:
.sp
.RS
.nf

\fBwhile ( n /= 10 > 1) ...
if (!"wk" ~ /bwk/) ...
\fP
.fi
.RE
.LP
.LP
Several features have been added based on newer implementations of
\fIawk\fP:
.IP " *" 3
Multiple instances of \fB-f\fP \fIprogfile\fP are permitted.
.LP
.IP " *" 3
The new option \fB-v\fP \fIassignment.\fP
.LP
.IP " *" 3
The new predefined variable \fBENVIRON\fP.
.LP
.IP " *" 3
New built-in functions \fBtoupper\fP and \fBtolower\fP.
.LP
.IP " *" 3
More formatting capabilities are added to \fBprintf\fP to match the
ISO\ C standard.
.LP
.LP
The overall \fIawk\fP syntax has always been based on the C language,
with a few features from the shell command language and
other sources. Because of this, it is not completely compatible with
any other language, which has caused confusion for some users.
It is not the intent of the standard developers to address such issues.
A few relatively minor changes toward making the language
more compatible with the ISO\ C standard were made; most of these
changes are based on similar changes in recent
implementations, as described above. There remain several C-language
conventions that are not in \fIawk\fP. One of the notable
ones is the comma operator, which is commonly used to specify multiple
expressions in the C language \fBfor\fP statement. Also,
there are various places where \fIawk\fP is more restrictive than
the C language regarding the type of expression that can be used
in a given context. These limitations are due to the different features
that the \fIawk\fP language does provide.
.LP
Regular expressions in \fIawk\fP have been extended somewhat from
historical implementations to make them a pure superset of
extended regular expressions, as defined by IEEE\ Std\ 1003.1-2001
(see the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 9.4, Extended Regular Expressions).
The
main extensions are internationalization features and interval expressions.
Historical implementations of \fIawk\fP have long
supported backslash escape sequences as an extension to extended regular
expressions, and this extension has been retained despite
inconsistency with other utilities. The number of escape sequences
recognized in both extended regular expressions and strings has
varied (generally increasing with time) among implementations. The
set specified by IEEE\ Std\ 1003.1-2001 includes most
sequences known to be supported by popular implementations and by
the ISO\ C standard. One sequence that is not supported is
hexadecimal value escapes beginning with \fB'\\x'\fP . This would
allow values expressed in more than 9 bits to be used within
\fIawk\fP as in the ISO\ C standard. However, because this syntax
has a non-deterministic length, it does not permit the
subsequent character to be a hexadecimal digit. This limitation can
be dealt with in the C language by the use of lexical string
concatenation. In the \fIawk\fP language, concatenation could also
be a solution for strings, but not for extended regular
expressions (either lexical ERE tokens or strings used dynamically
as regular expressions). Because of this limitation, the feature
has not been added to IEEE\ Std\ 1003.1-2001.
.LP
When a string variable is used in a context where an extended regular
expression normally appears (where the lexical token ERE
is used in the grammar) the string does not contain the literal slashes.
.LP
Some versions of \fIawk\fP allow the form:
.sp
.RS
.nf

\fBfunc name(args, ... ) { statements }
\fP
.fi
.RE
.LP
This has been deprecated by the authors of the language, who asked
that it not be specified.
.LP
Historical implementations of \fIawk\fP produce an error if a \fBnext\fP
statement is executed in a \fBBEGIN\fP action, and
cause \fIawk\fP to terminate if a \fBnext\fP statement is executed
in an \fBEND\fP action. This behavior has not been
documented, and it was not believed that it was necessary to standardize
it.
.LP
The specification of conversions between string and numeric values
is much more detailed than in the documentation of historical
implementations or in the referenced \fIThe AWK Programming Language\fP.
Although most of the behavior is designed to be
intuitive, the details are necessary to ensure compatible behavior
from different implementations. This is especially important in
relational expressions since the types of the operands determine whether
a string or numeric comparison is performed. From the
perspective of an application writer, it is usually sufficient to
expect intuitive behavior and to force conversions (by adding
zero or concatenating a null string) when the type of an expression
does not obviously match what is needed. The intent has been to
specify historical practice in almost all cases. The one exception
is that, in historical implementations, variables and constants
maintain both string and numeric values after their original value
is converted by any use. This means that referencing a variable
or constant can have unexpected side effects. For example, with historical
implementations the following program:
.sp
.RS
.nf

\fB{
    a = "+2"
    b = 2
    if (NR % 2)
        c = a + b
    if (a == b)
        print "numeric comparison"
    else
        print "string comparison"
}
\fP
.fi
.RE
.LP
would perform a numeric comparison (and output numeric comparison)
for each odd-numbered line, but perform a string comparison
(and output string comparison) for each even-numbered line. IEEE\ Std\ 1003.1-2001
ensures that comparisons will be numeric
if necessary. With historical implementations, the following program:
.sp
.RS
.nf

\fBBEGIN {
    OFMT = "%e"
    print 3.14
    OFMT = "%f"
    print 3.14
}
\fP
.fi
.RE
.LP
would output \fB"3.140000e+00"\fP twice, because in the second \fBprint\fP
statement the constant \fB"3.14"\fP would have
a string value from the previous conversion. IEEE\ Std\ 1003.1-2001
requires that the output of the second \fBprint\fP
statement be \fB"3.140000"\fP . The behavior of historical implementations
was seen as too unintuitive and unpredictable.
.LP
It was pointed out that with the rules contained in early drafts,
the following script would print nothing:
.sp
.RS
.nf

\fBBEGIN {
    y[1.5] = 1
    OFMT = "%e"
    print y[1.5]
}
\fP
.fi
.RE
.LP
Therefore, a new variable, \fBCONVFMT\fP, was introduced. The \fBOFMT\fP
variable is now restricted to affecting output
conversions of numbers to strings and \fBCONVFMT\fP is used for internal
conversions, such as comparisons or array indexing. The
default value is the same as that for \fBOFMT\fP, so unless a program
changes \fBCONVFMT\fP (which no historical program would
do), it will receive the historical behavior associated with internal
string conversions.
.LP
The POSIX \fIawk\fP lexical and syntactic conventions are specified
more formally than in other sources. Again the intent has
been to specify historical practice. One convention that may not be
obvious from the formal grammar as in other verbal descriptions
is where <newline>s are acceptable. There are several obvious placements
such as terminating a statement, and a backslash can
be used to escape <newline>s between any lexical tokens. In addition,
<newline>s without backslashes can follow a
comma, an open brace, a logical AND operator ( \fB"&&"\fP ), a logical
OR operator ( \fB"||"\fP ), the \fBdo\fP
keyword, the \fBelse\fP keyword, and the closing parenthesis of an
\fBif\fP, \fBfor\fP, or \fBwhile\fP statement. For
example:
.sp
.RS
.nf

\fB{ print $1,
        $2 }
\fP
.fi
.RE
.LP
The requirement that \fIawk\fP add a trailing <newline> to the program
argument text is to simplify the grammar, making
it match a text file in form. There is no way for an application or
test suite to determine whether a literal <newline> is
added or whether \fIawk\fP simply acts as if it did.
.LP
IEEE\ Std\ 1003.1-2001 requires several changes from historical implementations
in order to support
internationalization. Probably the most subtle of these is the use
of the decimal-point character, defined by the \fILC_NUMERIC\fP
category of the locale, in representations of floating-point numbers.
This locale-specific character is used in recognizing numeric
input, in converting between strings and numeric values, and in formatting
output. However, regardless of locale, the period
character (the decimal-point character of the POSIX locale) is the
decimal-point character recognized in processing \fIawk\fP
programs (including assignments in command line arguments). This is
essentially the same convention as the one used in the
ISO\ C standard. The difference is that the C language includes the
\fIsetlocale\fP() function, which permits an application to modify
its locale. Because of this
capability, a C application begins executing with its locale set to
the C locale, and only executes in the environment-specified
locale after an explicit call to \fIsetlocale\fP(). However, adding
such an elaborate
new feature to the \fIawk\fP language was seen as inappropriate for
IEEE\ Std\ 1003.1-2001. It is possible to execute an
\fIawk\fP program explicitly in any desired locale by setting the
environment in the shell.
.LP
The undefined behavior resulting from NULs in extended regular expressions
allows future extensions for the GNU \fIgawk\fP
program to process binary data.
.LP
The behavior in the case of invalid \fIawk\fP programs (including
lexical, syntactic, and semantic errors) is undefined because
it was considered overly limiting on implementations to specify. In
most cases such errors can be expected to produce a diagnostic
and a non-zero exit status. However, some implementations may choose
to extend the language in ways that make use of certain
invalid constructs. Other invalid constructs might be deemed worthy
of a warning, but otherwise cause some reasonable behavior.
Still other constructs may be very difficult to detect in some implementations.
Also, different implementations might detect a
given error during an initial parsing of the program (before reading
any input files) while others might detect it when executing
the program after reading some input. Implementors should be aware
that diagnosing errors as early as possible and producing useful
diagnostics can ease debugging of applications, and thus make an implementation
more usable.
.LP
The unspecified behavior from using multi-character \fBRS\fP values
is to allow possible future extensions based on extended
regular expressions used for record separators. Historical implementations
take the first character of the string and ignore the
others.
.LP
Unspecified behavior when \fIsplit\fP( \fIstring\fP, \fIarray\fP,
<null>) is used
is to allow a proposed future extension that would split up a string
into an array of individual characters.
.LP
In the context of the \fBgetline\fP function, equally good arguments
for different precedences of the \fB|\fP and \fB<\fP
operators can be made. Historical practice has been that:
.sp
.RS
.nf

\fBgetline < "a" "b"
\fP
.fi
.RE
.LP
is parsed as:
.sp
.RS
.nf

\fB( getline < "a" ) "b"
\fP
.fi
.RE
.LP
although many would argue that the intent was that the file \fBab\fP
should be read. However:
.sp
.RS
.nf

\fBgetline < "x" + 1
\fP
.fi
.RE
.LP
parses as:
.sp
.RS
.nf

\fBgetline < ( "x" + 1 )
\fP
.fi
.RE
.LP
Similar problems occur with the \fB|\fP version of \fBgetline\fP,
particularly in combination with \fB$\fP. For example:
.sp
.RS
.nf

\fB$"echo hi" | getline
\fP
.fi
.RE
.LP
(This situation is particularly problematic when used in a \fBprint\fP
statement, where the \fB|getline\fP part might be a
redirection of the \fBprint\fP.)
.LP
Since in most cases such constructs are not (or at least should not)
be used (because they have a natural ambiguity for which
there is no conventional parsing), the meaning of these constructs
has been made explicitly unspecified. (The effect is that a
conforming application that runs into the problem must parenthesize
to resolve the ambiguity.) There appeared to be few if any
actual uses of such constructs.
.LP
Grammars can be written that would cause an error under these circumstances.
Where backwards-compatibility is not a large
consideration, implementors may wish to use such grammars.
.LP
Some historical implementations have allowed some built-in functions
to be called without an argument list, the result being a
default argument list chosen in some "reasonable" way. Use of \fBlength\fP
as a synonym for \fBlength($0)\fP is the only one of
these forms that is thought to be widely known or widely used; this
particular form is documented in various places (for example,
most historical \fIawk\fP reference pages, although not in the referenced
\fIThe AWK Programming Language\fP) as legitimate
practice. With this exception, default argument lists have always
been undocumented and vaguely defined, and it is not at all clear
how (or if) they should be generalized to user-defined functions.
They add no useful functionality and preclude possible future
extensions that might need to name functions without calling them.
Not standardizing them seems the simplest course. The standard
developers considered that \fBlength\fP merited special treatment,
however, since it has been documented in the past and sees
possibly substantial use in historical programs. Accordingly, this
usage has been made legitimate, but Issue\ 5 removed the
obsolescent marking for XSI-conforming implementations and many otherwise
conforming applications depend on this feature.
.LP
In \fBsub\fP and \fBgsub\fP, if \fIrepl\fP is a string literal (the
lexical token \fBSTRING\fP), then two consecutive
backslash characters should be used in the string to ensure a single
backslash will precede the ampersand when the resultant string
is passed to the function. (For example, to specify one literal ampersand
in the replacement string, use \fBgsub\fP( \fBERE\fP,
\fB"\\\\&"\fP ).)
.LP
Historically the only special character in the \fIrepl\fP argument
of \fBsub\fP and \fBgsub\fP string functions was the
ampersand ( \fB'&'\fP ) character and preceding it with the backslash
character was used to turn off its special
meaning.
.LP
The description in the ISO\ POSIX-2:1993 standard introduced behavior
such that the backslash character was another special
character and it was unspecified whether there were any other special
characters. This description introduced several portability
problems, some of which are described below, and so it has been replaced
with the more historical description. Some of the problems
include:
.IP " *" 3
Historically, to create the replacement string, a script could use
\fBgsub\fP( \fBERE\fP, \fB"\\\\&"\fP ), but with the
ISO\ POSIX-2:1993 standard wording, it was necessary to use \fBgsub\fP(
\fBERE\fP, \fB"\\\\\\\\&"\fP ). Backslash
characters are doubled here because all string literals are subject
to lexical analysis, which would reduce each pair of backslash
characters to a single backslash before being passed to \fBgsub\fP.
.LP
.IP " *" 3
Since it was unspecified what the special characters were, for portable
scripts to guarantee that characters are printed
literally, each character had to be preceded with a backslash. (For
example, a portable script had to use \fBgsub\fP( \fBERE\fP,
\fB"\\\\h\\\\i"\fP ) to produce a replacement string of \fB"hi"\fP
\&.)
.LP
.LP
The description for comparisons in the ISO\ POSIX-2:1993 standard
did not properly describe historical practice because of
the way numeric strings are compared as numbers. The current rules
cause the following code:
.sp
.RS
.nf

\fBif (0 == "000")
    print "strange, but true"
else
    print "not true"
\fP
.fi
.RE
.LP
to do a numeric comparison, causing the \fBif\fP to succeed. It should
be intuitively obvious that this is incorrect behavior,
and indeed, no historical implementation of \fIawk\fP actually behaves
this way.
.LP
To fix this problem, the definition of \fInumeric string\fP was enhanced
to include only those values obtained from specific
circumstances (mostly external sources) where it is not possible to
determine unambiguously whether the value is intended to be a
string or a numeric.
.LP
Variables that are assigned to a numeric string shall also be treated
as a numeric string. (For example, the notion of a numeric
string can be propagated across assignments.) In comparisons, all
variables having the uninitialized value are to be treated as a
numeric operand evaluating to the numeric value zero.
.LP
Uninitialized variables include all types of variables including scalars,
array elements, and fields. The definition of an
uninitialized value in Variables and Special Variables is necessary
to describe the value placed on
uninitialized variables and on fields that are valid (for example,
\fB<\fP \fB$NF\fP) but have no characters in them and to
describe how these variables are to be used in comparisons. A valid
field, such as \fB$1\fP, that has no characters in it can be
obtained from an input line of \fB"\\t\\t"\fP when \fBFS=\fP \fB'\\t'\fP
\&. Historically, the comparison ( \fB$1<\fP10) was
done numerically after evaluating \fB$1\fP to the value zero.
.LP
The phrase "... also shall have the numeric value of the numeric string"
was removed from several sections of the
ISO\ POSIX-2:1993 standard because is specifies an unnecessary implementation
detail. It is not necessary for
IEEE\ Std\ 1003.1-2001 to specify that these objects be assigned two
different values. It is only necessary to specify that
these objects may evaluate to two different values depending on context.
.LP
The description of numeric string processing is based on the behavior
of the \fIatof\fP()
function in the ISO\ C standard. While it is not a requirement for
an implementation to use this function, many historical
implementations of \fIawk\fP do. In the ISO\ C standard, floating-point
constants use a period as a decimal point character
for the language itself, independent of the current locale, but the
\fIatof\fP() function and
the associated \fIstrtod\fP() function use the decimal point character
of the current
locale when converting strings to numeric values. Similarly in \fIawk\fP,
floating-point constants in an \fIawk\fP script use a
period independent of the locale, but input strings use the decimal
point character of the locale.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIGrammar Conventions\fP, \fIgrep\fP, \fIlex\fP, \fIsed\fP, the
System Interfaces volume of IEEE\ Std\ 1003.1-2001, \fIatof\fP(),
\fIexec\fP, \fIpopen\fP(), \fIsetlocale\fP(), \fIstrtod\fP()
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .