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.\"
.TH AWK 1 "June 13, 2021"
.SH NAME
awk \- pattern scanning and processing language
.SH SYNOPSIS
.nf
\fB/usr/bin/awk\fR [\fB-F\fR \fIERE\fR] [\fB-v\fR \fIassignment\fR] \fI\&'program'\fR | \fB-f\fR \fIprogfile\fR...
     [\fIargument\fR]...
.fi

.LP
.nf
\fB/usr/bin/nawk\fR [\fB-F\fR \fIERE\fR] [\fB-v\fR \fIassignment\fR] \fI\&'program'\fR | \fB-f\fR \fIprogfile\fR...
     [\fIargument\fR]...
.fi

.LP
.nf
\fB/usr/xpg4/bin/awk\fR [\fB-F\fR \fIERE\fR] [\fB-v\fR \fIassignment\fR]... \fI\&'program'\fR | \fB-f\fR \fIprogfile\fR...
     [\fIargument\fR]...
.fi

.SH DESCRIPTION
NOTE: The \fBnawk\fR command is now the system default awk for illumos.
.LP
The \fB/usr/bin/awk\fR and \fB/usr/xpg4/bin/awk\fR utilities execute
\fIprogram\fRs written in the \fBawk\fR programming language, which is
specialized for textual data manipulation. A \fBawk\fR \fIprogram\fR is a
sequence of patterns and corresponding actions. The string specifying
\fIprogram\fR must be enclosed in single quotes (') to protect it from
interpretation by the shell. The sequence of pattern - action statements can be
specified in the command line as \fIprogram\fR or in one, or more, file(s)
specified by the \fB-f\fR\fIprogfile\fR option. When input is read that matches
a pattern, the action associated with the pattern is performed.
.sp
.LP
Input is interpreted as a sequence of records. By default, a record is a line,
but this can be changed by using the \fBRS\fR built-in variable. Each record of
input is matched to each pattern in the \fIprogram\fR. For each pattern
matched, the associated action is executed.
.sp
.LP
The \fBawk\fR utility interprets each input record as a sequence of fields
where, by default, a field is a string of non-blank characters. This default
white-space field delimiter (blanks and/or tabs) can be changed by using the
\fBFS\fR built-in variable or the \fB-F\fR\fIERE\fR option. The \fBawk\fR
utility denotes the first field in a record \fB$1\fR, the second \fB$2\fR, and
so forth. The symbol \fB$0\fR refers to the entire record; setting any other
field causes the reevaluation of \fB$0\fR. Assigning to \fB$0\fR resets the
values of all fields and the \fBNF\fR built-in variable.

.SH OPTIONS
The following options are supported:
.sp
.ne 2
.na
\fB\fB-F\fR \fIERE\fR\fR
.ad
.RS 17n
Define the input field separator to be the extended regular expression
\fIERE\fR, before any input is read (can be a character).
.RE

.sp
.ne 2
.na
\fB\fB-f\fR \fIprogfile\fR\fR
.ad
.RS 17n
Specifies the pathname of the file \fIprogfile\fR containing a \fBawk\fR
program. If multiple instances of this option are specified, the concatenation
of the files specified as \fIprogfile\fR in the order specified is the
\fBawk\fR program. The \fBawk\fR program can alternatively be specified in
the command line as a single argument.
.RE

.sp
.ne 2
.na
\fB\fB-v\fR \fIassignment\fR\fR
.ad
.RS 17n
The \fIassignment\fR argument must be in the same form as an \fIassignment\fR
operand. The assignment is of the form \fIvar=value\fR, where \fIvar\fR is the
name of one of the variables described below. The specified assignment occurs
before executing the \fBawk\fR program, including the actions associated with
\fBBEGIN\fR patterns (if any). Multiple occurrences of this option can be
specified.
.RE

.sp
.ne 2
.na
\fB\fB-safe\fR\fR
.ad
.RS 17n
When passed to \fBawk\fR, this flag will prevent the program from opening new
files or running child processes. The \fBENVIRON\fR array will also not be
initialized.
.RE

.SH OPERANDS
The following operands are supported:
.sp
.ne 2
.na
\fB\fIprogram\fR\fR
.ad
.RS 12n
If no \fB-f\fR option is specified, the first operand to \fBawk\fR is the text
of the \fBawk\fR program. The application supplies the \fIprogram\fR operand
as a single argument to \fBawk.\fR If the text does not end in a newline
character, \fBawk\fR interprets the text as if it did.
.RE

.sp
.ne 2
.na
\fB\fIargument\fR\fR
.ad
.RS 12n
Either of the following two types of \fIargument\fR can be intermixed:
.sp
.ne 2
.na
\fB\fIfile\fR\fR
.ad
.RS 14n
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\fR operands are
specified, or if a \fIfile\fR operand is \fB\(mi\fR, the standard input is
used.
.RE

.sp
.ne 2
.na
\fB\fIassignment\fR\fR
.ad
.RS 14n
An operand that begins with an underscore or alphabetic character from the
portable character set, followed by a sequence of underscores, digits and
alphabetics from the portable character set, followed by the \fB=\fR character
specifies a variable assignment rather than a pathname. The characters before
the \fB=\fR represent the name of a \fBawk\fR variable. If that name is a
\fBawk\fR reserved word, the behavior is undefined. The characters following
the equal sign is interpreted as if they appeared in the \fBawk\fR program
preceded and followed by a double-quote (\fB"\fR) character, as a \fBSTRING\fR
token, except that if the last character is an unescaped backslash, it is
interpreted as a literal backslash rather than as the first character of the
sequence \fB\e\fR\&.. The variable is assigned the value of that \fBSTRING\fR
token. If the value is considered a \fInumeric\fR string, the variable is
assigned its numeric value. Each such variable assignment is performed just
before the processing of the following \fIfile\fR, if any. Thus, an assignment
before the first \fBfile\fR argument is executed after the \fBBEGIN\fR actions
(if any), while an assignment after the last \fIfile\fR argument is executed
before the \fBEND\fR actions (if any).  If there are no \fIfile\fR arguments,
assignments are executed before processing the standard input.
.RE

.RE

.SH INPUT FILES
Input files to the \fBawk\fR program from any of the following sources:
.RS +4
.TP
.ie t \(bu
.el o
any \fIfile\fR operands or their equivalents, achieved by modifying the
\fBawk\fR variables \fBARGV\fR and \fBARGC\fR
.RE
.RS +4
.TP
.ie t \(bu
.el o
standard input in the absence of any \fIfile\fR operands
.RE
.RS +4
.TP
.ie t \(bu
.el o
arguments to the \fBgetline\fR function
.RE
.sp
.LP
must be text files. Whether the variable \fBRS\fR is set to a value other than
a newline character or not, for these files, implementations support records
terminated with the specified separator up to \fB{LINE_MAX}\fR bytes and can
support longer records.
.sp
.LP
If \fB-\fR\fBf\fR \fIprogfile\fR is specified, the files named by each of the
\fIprogfile\fR option-arguments must be text files containing an \fBawk\fR
program.
.sp
.LP
The standard input are used only if no \fIfile\fR operands are specified, or if
a \fIfile\fR operand is \fB\(mi\fR\&.

.SH EXTENDED DESCRIPTION
A \fBawk\fR program is composed of pairs of the form:
.sp
.in +2
.nf
pattern { \fIaction\fR }
.fi
.in -2

.sp
.LP
Either the pattern or the action (including the enclosing brace characters) can
be omitted. Pattern-action statements are separated by a semicolon or by a
newline.
.sp
.LP
A missing pattern matches any record of input, and a missing action is
equivalent to an action that writes the matched record of input to standard
output.
.sp
.LP
Execution of the \fBawk\fR program starts by first executing the actions
associated with all \fBBEGIN\fR patterns in the order they occur in the
program. Then each \fIfile\fR operand (or standard input if no files were
specified) is processed by reading data from the file until a record separator
is seen (a newline character by default), splitting the current record into
fields using the current value of \fBFS\fR, evaluating each pattern in the
program in the order of occurrence, and executing the action associated with
each pattern that matches the current record. The action for a matching pattern
is executed before evaluating subsequent patterns. Last, the actions associated
with all \fBEND\fR patterns is executed in the order they occur in the program.

.SS "Expressions in awk"
Expressions describe computations used in \fIpatterns\fR and \fIactions\fR. 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 are evaluated before
lower precedence operators.  In this table \fIexpr,\fR \fIexpr1,\fR
\fIexpr2,\fR and \fIexpr3\fR represent any expression, while \fIlvalue\fR
represents any entity that can be assigned to (that is, on the left side of an
assignment operator).
.sp

.sp
.TS
c c c c
l l l l .
\fBSyntax\fR	\fBName\fR	\fBType of Result\fR	\fBAssociativity\fR
_
( \fIexpr\fR )	Grouping	type of \fIexpr\fR	n/a
_
$\fIexpr\fR	Field reference	string	n/a
_
++ \fIlvalue\fR	Pre-increment	numeric	n/a
\(mi\(mi \fIlvalue\fR	Pre-decrement	numeric	n/a
\fIlvalue\fR ++	Post-increment	numeric	n/a
\fIlvalue\fR \(mi\(mi	Post-decrement	numeric	n/a
_
\fIexpr\fR ^ \fIexpr\fR	Exponentiation	numeric	right
_
! \fIexpr\fR	Logical not	numeric	n/a
+ \fIexpr\fR	Unary plus	numeric	n/a
\(mi \fIexpr\fR	Unary minus	numeric	n/a
_
\fIexpr\fR * \fIexpr\fR	Multiplication	numeric	left
\fIexpr\fR / \fIexpr\fR	Division	numeric	left
\fIexpr\fR % \fIexpr\fR	Modulus	numeric	left
_
\fIexpr\fR + \fIexpr\fR	Addition	numeric	left
\fIexpr\fR \(mi \fIexpr\fR	Subtraction	numeric	left
_
\fIexpr\fR \fIexpr\fR	String concatenation	string	left
_
\fIexpr\fR < \fIexpr\fR	Less than	numeric	none
\fIexpr\fR <= \fIexpr\fR	Less than or equal to	numeric	none
\fIexpr\fR != \fIexpr\fR	Not equal to	numeric	none
\fIexpr\fR == \fIexpr\fR	Equal to	numeric	none
\fIexpr\fR > \fIexpr\fR	Greater than	numeric	none
\fIexpr\fR >= \fIexpr\fR	Greater than or equal to	numeric	none
_
\fIexpr\fR ~ \fIexpr\fR	ERE match	numeric	none
\fIexpr\fR !~ \fIexpr\fR	ERE non-match	 numeric	none
_
\fIexpr\fR in array	Array membership	numeric	left
( \fIindex\fR ) in	Multi-dimension array	numeric	left
    \fIarray\fR	    membership
_
\fBexpr\fR && \fIexpr\fR	Logical AND	numeric	left
_
\fBexpr\fR |\|| \fIexpr\fR	Logical OR	numeric	left
_
\fIexpr1\fR ? \fIexpr2\fR	Conditional expression	type of selected	right
    : \fIexpr3\fR		   \fIexpr2\fR or \fIexpr3\fR
_
\fIlvalue\fR ^= \fIexpr\fR	Exponentiation	numeric	right
	assignment
\fIlvalue\fR %= \fIexpr\fR	Modulus assignment	numeric	right
\fIlvalue\fR *= \fIexpr\fR	Multiplication	numeric	right
	assignment
\fIlvalue\fR /= \fIexpr\fR	Division assignment	numeric	right
\fIlvalue\fR +=  \fIexpr\fR	Addition assignment	numeric	right
\fIlvalue\fR \(mi= \fIexpr\fR	Subtraction assignment	numeric	right
\fIlvalue\fR = \fIexpr\fR	Assignment	type of \fIexpr\fR	right
.TE

.sp
.LP
Each expression has either a string value, a numeric value or both. Except as
stated for specific contexts, the value of an expression is implicitly
converted to the type needed for the context in which it is used.  A string
value is converted to a numeric value by the equivalent of the following calls:
.sp
.in +2
.nf
setlocale(LC_NUMERIC, "");
\fInumeric_value\fR = atof(\fIstring_value\fR);
.fi
.in -2

.sp
.LP
A numeric value that is exactly equal to the value of an integer is converted
to a string by the equivalent of a call to the \fBsprintf\fR function with the
string \fB%d\fR as the \fBfmt\fR argument and the numeric value being converted
as the first and only \fIexpr\fR argument.  Any other numeric value is
converted to a string by the equivalent of a call to the \fBsprintf\fR function
with the value of the variable \fBCONVFMT\fR as the \fBfmt\fR argument and the
numeric value being converted as the first and only \fIexpr\fR argument.
.sp
.LP
A string value is considered to be a \fInumeric string\fR in the following
case:
.RS +4
.TP
1.
Any leading and trailing blank characters is ignored.
.RE
.RS +4
.TP
2.
If the first unignored character is a \fB+\fR or \fB\(mi\fR, it is ignored.
.RE
.RS +4
.TP
3.
If the remaining unignored characters would be lexically recognized as a
\fBNUMBER\fR token, the string is considered a \fInumeric string\fR.
.RE
.sp
.LP
If a \fB\(mi\fR character is ignored in the above steps, the numeric value of
the \fInumeric string\fR is the negation of the numeric value of the recognized
\fBNUMBER\fR token. Otherwise the numeric value of the \fInumeric string\fR is
the numeric value of the recognized \fBNUMBER\fR token. Whether or not a string
is a \fInumeric string\fR is relevant only in contexts where that term is used
in this section.
.sp
.LP
When an expression is used in a Boolean context, if it has a numeric value, a
value of zero is treated as false and any other value is treated as true.
Otherwise, a string value of the null string is treated as false and any other
value is treated as true. A Boolean context is one of the following:
.RS +4
.TP
.ie t \(bu
.el o
the first subexpression of a conditional expression.
.RE
.RS +4
.TP
.ie t \(bu
.el o
an expression operated on by logical NOT, logical \fBAND,\fR or logical OR.
.RE
.RS +4
.TP
.ie t \(bu
.el o
the second expression of a \fBfor\fR statement.
.RE
.RS +4
.TP
.ie t \(bu
.el o
the expression of an \fBif\fR statement.
.RE
.RS +4
.TP
.ie t \(bu
.el o
the expression of the \fBwhile\fR clause in either a \fBwhile\fR or \fBdo\fR
\fB\&.\|.\|.\fR \fBwhile\fR statement.
.RE
.RS +4
.TP
.ie t \(bu
.el o
an expression used as a pattern (as in Overall Program Structure).
.RE
.sp
.LP
The \fBawk\fR language supplies arrays that are used for storing numbers or
strings. Arrays need not be declared. They are initially empty, and their sizes
changes 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 \fIlvalue\fR and as an
expression, as described in the grammar.  Unsubscripted array names are used in
only the following contexts:
.RS +4
.TP
.ie t \(bu
.el o
a parameter in a function definition or function call.
.RE
.RS +4
.TP
.ie t \(bu
.el o
the \fBNAME\fR token following any use of the keyword \fBin\fR.
.RE
.sp
.LP
A valid array \fIindex\fR consists of one or more comma-separated expressions,
similar to the way in which multi-dimensional arrays are indexed in some
programming languages. Because \fBawk\fR arrays are really one-dimensional,
such a comma-separated list is 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\fR variable.
.sp
.LP
Thus, the following two index operations are equivalent:
.sp
.in +2
.nf
var[expr1, expr2, ... exprn]
var[expr1 SUBSEP expr2 SUBSEP ... SUBSEP exprn]
.fi
.in -2

.sp
.LP
A multi-dimensioned \fIindex\fR used with the \fBin\fR operator must be put in
parentheses. The \fBin\fR operator, which tests for the existence of a
particular array element, does not create the element if it does not exist.
Any other reference to a non-existent array element automatically creates it.

.SS "Variables and Special Variables"
Variables can be used in an \fBawk\fR program by referencing them. With the
exception of function parameters, they are not explicitly declared.
Uninitialized scalar variables and array elements have both a numeric value of
zero and a string value of the empty string.
.sp
.LP
Field variables are designated by a \fB$\fR followed by a number or numerical
expression. The effect of the field number \fIexpression\fR evaluating to
anything other than a non-negative integer is unspecified. Uninitialized
variables or string values need not be converted to numeric values in this
context. New field variables are created by assigning a value to them.
References to non-existent fields (that is, fields after \fB$NF\fR) produce the
null string. However, assigning to a non-existent field (for example,
\fB$(NF+2) = 5\fR) increases the value of \fBNF\fR, create any intervening
fields with the null string as their values and cause the value of \fB$0\fR to
be recomputed, with the fields being separated by the value of \fBOFS\fR. Each
field variable has a string value when created. If the string, with any
occurrence of the decimal-point character from the current locale changed to a
period character, is considered a \fInumeric string\fR (see \fBExpressions in
awk\fR above), the field variable also has the numeric value of the \fInumeric
string\fR.

.SS "/usr/bin/awk, /usr/xpg4/bin/awk"
\fBawk\fR sets the following special variables that are supported by both
\fB/usr/bin/awk\fR and \fB/usr/xpg4/bin/awk\fR:
.sp
.ne 2
.na
\fB\fBARGC\fR\fR
.ad
.RS 12n
The number of elements in the \fBARGV\fR array.
.RE

.sp
.ne 2
.na
\fB\fBARGV\fR\fR
.ad
.RS 12n
An array of command line arguments, excluding options and the \fIprogram\fR
argument, numbered from zero to \fBARGC\fR\(mi1.
.sp
The arguments in \fBARGV\fR can be modified or added to; \fBARGC\fR can be
altered.  As each input file ends, \fBawk\fR treats the next non-null element
of \fBARGV\fR, up to the current value of \fBARGC\fR\(mi1, inclusive, as the
name of the next input file.  Setting an element of \fBARGV\fR to null means
that it is not treated as an input file. The name \fB\(mi\fR indicates the
standard input. If an argument matches the format of an \fIassignment\fR
operand, this argument is treated as an assignment rather than a \fIfile\fR
argument.
.RE

.sp
.ne 2
.na
\fB\fBCONVFMT\fR\fR
.ad
.RS 12n
The \fBprintf\fR format for converting numbers to strings (except for output
statements, where \fBOFMT\fR is used). The default is \fB%.6g\fR.
.RE

.sp
.ne 2
.na
\fB\fBENVIRON\fR\fR
.ad
.RS 12n
The variable \fBENVIRON\fR is an array representing the value of the
environment. The indices of the array are strings consisting of the names of
the environment variables, and the value of each array element is a string
consisting of the value of that variable. If the value of an environment
variable is considered a \fInumeric string\fR, the array element also has its
numeric value.
.sp
In all cases where \fBawk\fR behavior is affected by environment variables
(including the environment of any commands that \fBawk\fR executes via the
\fBsystem\fR function or via pipeline redirections with the \fBprint\fR
statement, the \fBprintf\fR statement, or the \fBgetline\fR function), the
environment used is the environment at the time \fBawk\fR began executing.
.RE

.sp
.ne 2
.na
\fB\fBFILENAME\fR\fR
.ad
.RS 12n
A pathname of the current input file. Inside a \fBBEGIN\fR action the value is
undefined. Inside an \fBEND\fR action the value is the name of the last input
file processed.
.RE

.sp
.ne 2
.na
\fB\fBFNR\fR\fR
.ad
.RS 12n
The ordinal number of the current record in the current file. Inside a
\fBBEGIN\fR action the value is zero. Inside an \fBEND\fR action the value is
the number of the last record processed in the last file processed.
.RE

.sp
.ne 2
.na
\fB\fBFS\fR\fR
.ad
.RS 12n
Input field separator regular expression; a space character by default.
.RE

.sp
.ne 2
.na
\fB\fBNF\fR\fR
.ad
.RS 12n
The number of fields in the current record. Inside a \fBBEGIN\fR action, the
use of \fBNF\fR is undefined unless a \fBgetline\fR function without a
\fIvar\fR argument is executed previously. Inside an \fBEND\fR action, \fBNF\fR
retains the value it had for the last record read, unless a subsequent,
redirected, \fBgetline\fR function without a \fIvar\fR argument is performed
prior to entering the \fBEND\fR action.
.RE

.sp
.ne 2
.na
\fB\fBNR\fR\fR
.ad
.RS 12n
The ordinal number of the current record from the start of input. Inside a
\fBBEGIN\fR action the value is zero. Inside an \fBEND\fR action the value is
the number of the last record processed.
.RE

.sp
.ne 2
.na
\fB\fBOFMT\fR\fR
.ad
.RS 12n
The \fBprintf\fR format for converting numbers to strings in output statements
\fB"%.6g"\fR by default. The result of the conversion is unspecified if the
value of \fBOFMT\fR is not a floating-point format specification.
.RE

.sp
.ne 2
.na
\fB\fBOFS\fR\fR
.ad
.RS 12n
The \fBprint\fR statement output field separator; a space character by default.
.RE

.sp
.ne 2
.na
\fB\fBORS\fR\fR
.ad
.RS 12n
The \fBprint\fR output record separator; a newline character by default.
.RE

.sp
.ne 2
.na
\fB\fBRLENGTH\fR\fR
.ad
.RS 12n
The length of the string matched by the \fBmatch\fR function.
.RE

.sp
.ne 2
.na
\fB\fBRS\fR\fR
.ad
.RS 12n
The first character of the string value of \fBRS\fR is the input record
separator; a newline character by default. If \fBRS\fR contains more than one
character, the results are unspecified. If \fBRS\fR is null, then records are
separated by sequences of one or more blank lines. Leading or trailing blank
lines do not produce empty records at the beginning or end of input, and the
field separator is always newline, no matter what the value of \fBFS\fR.
.RE

.sp
.ne 2
.na
\fB\fBRSTART\fR\fR
.ad
.RS 12n
The starting position of the string matched by the \fBmatch\fR function,
numbering from 1. This is always equivalent to the return value of the
\fBmatch\fR function.
.RE

.sp
.ne 2
.na
\fB\fBSUBSEP\fR\fR
.ad
.RS 12n
The subscript separator string for multi-dimensional arrays. The default value
is \fB\e034\fR\&.
.RE

.SS "/usr/bin/awk"
The following variable is supported for \fB/usr/bin/awk\fR only:
.sp
.ne 2
.na
\fB\fBRT\fR\fR
.ad
.RS 12n
The record terminator for the most recent record read. For most records this
will be the same value as \fBRS\fR. At the end of a file with no trailing
separator value, though, this will be set to the empty string (\fB""\fR).
.RE

.SS "Regular Expressions"
The \fBawk\fR utility makes use of the extended regular expression notation
(see \fBregex\fR(5)) except that it allows the use of C-language conventions to
escape special characters within the EREs, namely \fB\e\e\fR, \fB\ea\fR,
\fB\eb\fR, \fB\ef\fR, \fB\en\fR, \fB\er\fR, \fB\et\fR, \fB\ev\fR, and those
specified in the following table.  These escape sequences are recognized both
inside and outside bracket expressions.  Note that records need not be
separated by newline characters and string constants can contain newline
characters, so even the \fB\en\fR sequence is valid in \fBawk\fR EREs.  Using
a slash character within the regular expression requires escaping as shown in
the table below:
.sp

.sp
.TS
l l l
l l l .
\fBEscape Sequence\fR	\fBDescription\fR	\fBMeaning\fR
_
\fB\e"\fR	Backslash quotation-mark	Quotation-mark character
_
\fB\e/\fR	Backslash slash	Slash character
_
\fB\e\fR\fIddd\fR	T{
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 NULL character), the behavior is undefined.
T}	T{
The character encoded by the one-, two- or three-digit octal integer. Multi-byte characters require multiple, concatenated escape sequences, including the leading \e for each byte.
T}
_
\fB\e\fR\fIc\fR	T{
A backslash character followed by any character not described in this table or special characters (\fB\e\e\fR, \fB\ea\fR, \fB\eb\fR, \fB\ef\fR, \fB\en\fR, \fB\er\fR, \fB\et\fR, \fB\ev\fR).
T}	Undefined
.TE

.sp
.LP
A regular expression can be matched against a specific field or string by using
one of the two regular expression matching operators, \fB~\fR and \fB!\|~\fR.
These operators 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~\fR expression evaluates to the value \fB1\fR, and the
\fB!\|~\fR expression evaluates to the value \fB0\fR. If the regular expression
does not match the string, the \fB~\fR expression evaluates to the value
\fB0\fR, and the \fB!\|~\fR expression evaluates to the value \fB1\fR. If the
right-hand operand is any expression other than the lexical token \fBERE\fR,
the string value of the expression is interpreted as an extended regular
expression, including the escape conventions described above. Notice that these
same escape conventions also are applied in the determining the value of a
string literal (the lexical token \fBSTRING\fR), and is applied a second time
when a string literal is used in this context.
.sp
.LP
When an \fBERE\fR token appears as an expression in any context other than as
the right-hand of the \fB~\fR or \fB!\|~\fR operator or as one of the built-in
function arguments described below, the value of the resulting expression is
the equivalent of:
.sp
.in +2
.nf
$0 ~ /\fIere\fR/
.fi
.in -2

.sp
.LP
The \fIere\fR argument to the \fBgsub,\fR \fBmatch,\fR \fBsub\fR functions, and
the \fIfs\fR argument to the \fBsplit\fR function (see \fBString Functions\fR)
is interpreted as extended regular expressions. These can be either \fBERE\fR
tokens or arbitrary expressions, and are interpreted in the same manner as the
right-hand side of the \fB~\fR or \fB!\|~\fR operator.
.sp
.LP
An extended regular expression can be used to separate fields by using the
\fB-F\fR \fIERE\fR option or by assigning a string containing the expression to
the built-in variable \fBFS\fR. The default value of the \fBFS\fR variable is a
single space character. The following describes \fBFS\fR behavior:
.RS +4
.TP
1.
If \fBFS\fR is a single character:
.RS +4
.TP
.ie t \(bu
.el o
If \fBFS\fR is the space character, skip leading and trailing blank characters;
fields are delimited by sets of one or more blank characters.
.RE
.RS +4
.TP
.ie t \(bu
.el o
Otherwise, if \fBFS\fR is any other character \fIc\fR, fields are delimited by
each single occurrence of \fIc\fR.
.RE
.RE
.RS +4
.TP
2.
Otherwise, the string value of \fBFS\fR is considered to be an extended
regular expression. Each occurrence of a sequence matching the extended regular
expression delimits fields.
.RE
.sp
.LP
Except in the \fBgsub\fR, \fBmatch\fR, \fBsplit\fR, and \fBsub\fR built-in
functions, regular expression matching is based on input records. That is,
record separator characters (the first character of the value of the variable
\fBRS\fR, a newline character by default) cannot be embedded in the expression,
and no expression matches the record separator character. If the record
separator is not a newline character, newline characters embedded in the
expression can be matched. In those four built-in functions, regular expression
matching are based on text strings. So, any character (including the newline
character and the record separator) can be embedded in the pattern and an
appropriate pattern matches any character. However, in all \fBawk\fR regular
expression matching, the use of one or more NULL characters in the pattern,
input record or text string produces undefined results.

.SS "Patterns"
A \fIpattern\fR is any valid \fIexpression,\fR a range specified by two
expressions separated by comma, or one of the two special patterns \fBBEGIN\fR
or \fBEND\fR.

.SS "Special Patterns"
The \fBawk\fR utility recognizes two special patterns, \fBBEGIN\fR and
\fBEND\fR. Each \fBBEGIN\fR pattern is matched once and its associated action
executed before the first record of input is read (except possibly by use of
the \fBgetline\fR function in a prior \fBBEGIN\fR action) and before command
line assignment is done. Each \fBEND\fR pattern is matched once and its
associated action executed after the last record of input has been read. These
two patterns have associated actions.
.sp
.LP
\fBBEGIN\fR and \fBEND\fR do not combine with other patterns.  Multiple
\fBBEGIN\fR and \fBEND\fR patterns are allowed. The actions associated with the
\fBBEGIN\fR patterns are executed in the order specified in the program, as are
the \fBEND\fR actions. An \fBEND\fR pattern can precede a \fBBEGIN\fR pattern
in a program.
.sp
.LP
If an \fBawk\fR program consists of only actions with the pattern \fBBEGIN\fR,
and the \fBBEGIN\fR action contains no \fBgetline\fR function, \fBawk\fR exits
without reading its input when the last statement in the last \fBBEGIN\fR
action is executed. If an \fBawk\fR program consists of only actions with the
pattern \fBEND\fR or only actions with the patterns \fBBEGIN\fR and \fBEND\fR,
the input is read before the statements in the \fBEND\fR actions are executed.

.SS "Expression Patterns"
An expression pattern is evaluated as if it were an expression in a Boolean
context. If the result is true, the pattern is considered to match, and the
associated action (if any) is executed. If the result is false, the action is
not executed.

.SS "Pattern Ranges"
A pattern range consists of two expressions separated by a comma. In this case,
the action is 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"
An action is a sequence of statements. A statement can be one of the following:
.sp
.in +2
.nf
if ( \fIexpression\fR ) \fIstatement\fR [ else \fIstatement\fR ]
while ( \fIexpression\fR ) \fIstatement\fR
do \fIstatement\fR while ( \fIexpression\fR )
for ( \fIexpression\fR ; \fIexpression\fR ; \fIexpression\fR ) \fIstatement\fR
for ( \fIvar\fR in \fIarray\fR ) \fIstatement\fR
delete \fIarray\fR[\fIsubscript\fR] #delete an array element
delete \fIarray\fR #delete all elements within an array
break
continue
{ [ \fIstatement\fR ] .\|.\|. }
\fIexpression\fR        # commonly variable = expression
print [ \fIexpression-list\fR ] [ >\fIexpression\fR ]
printf format [ ,\fIexpression-list\fR ] [ >\fIexpression\fR ]
next              # skip remaining patterns on this input line
nextfile          # skip remaining patterns on this input file
exit [expr] # skip the rest of the input; exit status is expr
return [expr]
.fi
.in -2

.sp
.LP
Any single statement can be replaced by a statement list enclosed in braces.
The statements are terminated by newline characters or semicolons, and are
executed sequentially in the order that they appear.
.sp
.LP
The \fBnext\fR statement causes all further processing of the current input
record to be abandoned. The behavior is undefined if a \fBnext\fR statement
appears or is invoked in a \fBBEGIN\fR or \fBEND\fR action.
.sp
.LP
The \fBnextfile\fR statement is similar to \fBnext\fR, but also skips all other
records in the current file, and moves on to processing the next input file if
available (or exits the program if there are none). (Note that this keyword is
not supported by \fB/usr/xpg4/bin/awk\fR.)
.sp
.LP
The \fBexit\fR statement invokes all \fBEND\fR actions in the order in which
they occur in the program source and then terminate the program without reading
further input. An \fBexit\fR statement inside an \fBEND\fR action terminates
the program without further execution of \fBEND\fR actions.  If an expression
is specified in an \fBexit\fR statement, its numeric value is the exit status
of \fBawk\fR, unless subsequent errors are encountered or a subsequent
\fBexit\fR statement with an expression is executed.

.SS "Output Statements"
Both \fBprint\fR and \fBprintf\fR statements write to standard output by
default.  The output is written to the location specified by
\fIoutput_redirection\fR if one is supplied, as follows:
.sp
.in +2
.nf
\fB>\fR \fIexpression\fR\fB>>\fR \fIexpression\fR\fB|\fR \fIexpression\fR
.fi
.in -2

.sp
.LP
In all cases, the \fIexpression\fR is evaluated to produce a string that is
used as a full pathname to write into (for \fB>\fR or \fB>>\fR) or as a command
to be executed (for \fB|\fR). Using the first two forms, if the file of that
name is not currently open, it is opened, creating it if necessary and using
the first form, truncating the file. The output then is appended to the file.
As long as the file remains open, subsequent calls in which \fIexpression\fR
evaluates to the same string value simply appends output to the file. The file
remains open until the \fBclose\fR function, which is called with an expression
that evaluates to the same string value.
.sp
.LP
The third form writes output onto a stream piped to the input of a command. The
stream is created if no stream is currently open with the value of
\fIexpression\fR as its command name.  The stream created is equivalent to one
created by a call to the \fBpopen\fR(3C) function with the value of
\fIexpression\fR as the \fIcommand\fR argument and a value of \fBw\fR as the
\fImode\fR argument.  As long as the stream remains open, subsequent calls in
which \fIexpression\fR evaluates to the same string value writes output to the
existing stream. The stream remains open until the \fBclose\fR function is
called with an expression that evaluates to the same string value.  At that
time, the stream is closed as if by a call to the \fBpclose\fR function.
.sp
.LP
These output statements take a comma-separated list of \fIexpression\fR \fIs\fR
referred in the grammar by the non-terminal symbols \fBexpr_list,\fR
\fBprint_expr_list\fR or \fBprint_expr_list_opt.\fR This list is referred to
here as the \fIexpression list\fR, and each member is referred to as an
\fIexpression argument\fR.
.sp
.LP
The \fBprint\fR statement writes the value of each expression argument onto the
indicated output stream separated by the current output field separator (see
variable \fBOFS\fR above), and terminated by the output record separator (see
variable \fBORS\fR above). All expression arguments is taken as strings, being
converted if necessary; with the exception that the \fBprintf\fR format in
\fBOFMT\fR is used instead of the value in \fBCONVFMT\fR. An empty expression
list stands for the whole input record \fB(\fR$0\fB)\fR.
.sp
.LP
The \fBprintf\fR statement produces output based on a notation similar to the
File Format Notation used to describe file formats in this document Output is
produced as specified with the first expression argument as the string
\fBformat\fR and subsequent expression arguments as the strings \fBarg1\fR to
\fBargn,\fR inclusive, with the following exceptions:
.RS +4
.TP
1.
The \fIformat\fR is an actual character string rather than a graphical
representation. Therefore, it cannot contain empty character positions. The
space character in the \fIformat\fR string, in any context other than a
\fIflag\fR of a conversion specification, is treated as an ordinary character
that is copied to the output.
.RE
.RS +4
.TP
2.
If the character set contains a Delta character and that character appears
in the \fIformat\fR string, it is treated as an ordinary character that is
copied to the output.
.RE
.RS +4
.TP
3.
The \fIescape sequences\fR beginning with a backslash character is treated
as sequences of ordinary characters that are copied to the output. Note that
these same sequences is interpreted lexically by \fBawk\fR when they appear in
literal strings, but they is not treated specially by the \fBprintf\fR
statement.
.RE
.RS +4
.TP
4.
A \fIfield width\fR or \fIprecision\fR can be specified as the \fB*\fR
character instead of a digit string. In this case the next argument from the
expression list is fetched and its numeric value taken as the field width or
precision.
.RE
.RS +4
.TP
5.
The implementation does not precede or follow output from the \fBd\fR or
\fBu\fR conversion specifications with blank characters not specified by the
\fIformat\fR string.
.RE
.RS +4
.TP
6.
The implementation does not precede output from the \fBo\fR conversion
specification with leading zeros not specified by the \fIformat\fR string.
.RE
.RS +4
.TP
7.
For the \fBc\fR conversion specification: if the argument has a numeric
value, the character whose encoding is that value is 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 is output; if the string does not contain any
characters the behavior is undefined.
.RE
.RS +4
.TP
8.
For each conversion specification that consumes an argument, the next
expression argument is evaluated. With the exception of the \fBc\fR conversion,
the value is converted to the appropriate type for the conversion
specification.
.RE
.RS +4
.TP
9.
If there are insufficient expression arguments to satisfy all the conversion
specifications in the \fIformat\fR string, the behavior is undefined.
.RE
.RS +4
.TP
10.
If any character sequence in the \fIformat\fR string begins with a %
character, but does not form a valid conversion specification, the behavior is
unspecified.
.RE
.sp
.LP
Both \fBprint\fR and \fBprintf\fR can output at least \fB{LINE_MAX}\fR bytes.

.SS "Functions"
The \fBawk\fR language has a variety of built-in functions: arithmetic,
string, input/output and general.

.SS "Arithmetic Functions"
The arithmetic functions, except for \fBint\fR, are based on the \fBISO\fR
\fBC\fR standard. The behavior is undefined in cases where the \fBISO\fR
\fBC\fR standard specifies that an error be returned or that the behavior is
undefined. Although the 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[ ]\fR
brackets), such use is undefined.
.sp
.ne 2
.na
\fB\fBatan2(\fR\fIy\fR,\fIx\fR\fB)\fR\fR
.ad
.RS 17n
Return arctangent of \fIy\fR/\fIx\fR.
.RE

.sp
.ne 2
.na
\fB\fBcos\fR(\fIx\fR)\fR
.ad
.RS 17n
Return cosine of \fIx,\fR where \fIx\fR is in radians.
.RE

.sp
.ne 2
.na
\fB\fBsin\fR(\fIx\fR)\fR
.ad
.RS 17n
Return sine of \fIx,\fR where \fIx\fR is in radians.
.RE

.sp
.ne 2
.na
\fB\fBexp\fR(\fIx\fR)\fR
.ad
.RS 17n
Return the exponential function of \fIx\fR.
.RE

.sp
.ne 2
.na
\fB\fBlog\fR(\fIx\fR)\fR
.ad
.RS 17n
Return the natural logarithm of \fIx\fR.
.RE

.sp
.ne 2
.na
\fB\fBsqrt\fR(\fIx\fR)\fR
.ad
.RS 17n
Return the square root of \fIx\fR.
.RE

.sp
.ne 2
.na
\fB\fBint\fR(\fIx\fR)\fR
.ad
.RS 17n
Truncate its argument to an integer. It is truncated toward 0 when \fIx\fR > 0.
.RE

.sp
.ne 2
.na
\fB\fBrand()\fR\fR
.ad
.RS 17n
Return a random number \fIn\fR, such that 0 \(<= \fIn\fR < 1.
.RE

.sp
.ne 2
.na
\fB\fBsrand\fR([\fBexpr\fR])\fR
.ad
.RS 17n
Set the seed value for \fBrand\fR to \fIexpr\fR or use the time of day if
\fIexpr\fR is omitted. The previous seed value is returned.
.RE

.SS "String Functions"
The string functions in the following list shall be supported. Although the
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[ ]\fR brackets), such use is undefined.
.sp
.ne 2
.na
\fB\fBgsub\fR(\fIere\fR,\fIrepl\fR[,\|\fIin\fR])\fR
.ad
.sp .6
.RS 4n
Behave like \fBsub\fR (see below), except that it replaces all occurrences of
the regular expression (like the \fBed\fR utility global substitute) in
\fB$0\fR or in the \fIin\fR argument, when specified.
.RE

.sp
.ne 2
.na
\fB\fBindex\fR(\fIs\fR,\fIt\fR)\fR
.ad
.sp .6
.RS 4n
Return the position, in characters, numbering from 1, in string \fIs\fR where
string \fIt\fR first occurs, or zero if it does not occur at all.
.RE

.sp
.ne 2
.na
\fB\fBlength\fR[([\fIv\fR])]\fR
.ad
.sp .6
.RS 4n
Given no argument, this function returns the length of the whole record,
\fB$0\fR. If given an array as an argument (and using \fB/usr/bin/awk\fR),
then this returns the number of elements it contains. Otherwise, this function
interprets the argument as a string (performing any needed conversions) and
returns its length in characters.
.RE

.sp
.ne 2
.na
\fB\fBmatch\fR(\fIs\fR,\fIere\fR)\fR
.ad
.sp .6
.RS 4n
Return the position, in characters, numbering from 1, in string \fIs\fR where
the extended regular expression \fIere\fR occurs, or zero if it does not occur
at all. \fBRSTART\fR is set to the starting position (which is the same as the
returned value), zero if no match is found; \fBRLENGTH\fR is set to the length
of the matched string, \(mi1 if no match is found.
.RE

.sp
.ne 2
.na
\fB\fBsplit\fR(\fIs\fR,\fIa\fR[,\|\fIfs\fR])\fR
.ad
.sp .6
.RS 4n
Split the string \fIs\fR into array elements \fIa\fR[1], \fIa\fR[2],
\fB\&...,\fR \fIa\fR[\fIn\fR], and return \fIn\fR. The separation is done with
the extended regular expression \fIfs\fR or with the field separator \fBFS\fR
if \fIfs\fR is not given. Each array element has a string value when created.
If the string assigned to any array element, with any occurrence of the
decimal-point character from the current locale changed to a period character,
would be considered a \fInumeric string\fR; the array element also has the
numeric value of the \fInumeric string\fR. The effect of a null string as the
value of \fIfs\fR is unspecified.
.RE

.sp
.ne 2
.na
\fB\fBsprintf\fR(\fBfmt\fR,\fIexpr\fR,\fIexpr\fR,\fB\&...\fR)\fR
.ad
.sp .6
.RS 4n
Format the expressions according to the \fBprintf\fR format given by \fIfmt\fR
and return the resulting string.
.RE

.sp
.ne 2
.na
\fB\fBsub\fR(\fIere\fR,\fIrepl\fR[,\|\fIin\fR])\fR
.ad
.sp .6
.RS 4n
Substitute the string \fIrepl\fR in place of the first instance of the extended
regular expression \fBERE\fR in string in and return the number of
substitutions. An ampersand ( \fB&\fR ) appearing in the string \fIrepl\fR is
replaced by the string from in that matches the regular expression. An
ampersand preceded with a backslash ( \fB\e\fR ) is interpreted as the literal
ampersand character. An occurrence of two consecutive backslashes is
interpreted as just a single literal backslash character.  Any other occurrence
of a backslash (for example, preceding any other character) is treated as a
literal backslash character. If \fIrepl\fR is a string literal, the handling of
the ampersand character occurs after any lexical processing, including any
lexical backslash escape sequence processing. If \fBin\fR is specified and it
is not an \fBlvalue\fR the behavior is undefined. If in is omitted, \fBawk\fR
uses the current record (\fB$0\fR) in its place.
.RE

.sp
.ne 2
.na
\fB\fBsubstr\fR(\fIs\fR,\fIm\fR[,\|\fIn\fR])\fR
.ad
.sp .6
.RS 4n
Return the at most \fIn\fR-character substring of \fIs\fR that begins at
position \fIm,\fR numbering from 1. If \fIn\fR is missing, the length of the
substring is limited by the length of the string \fIs\fR.
.RE

.sp
.ne 2
.na
\fB\fBtolower\fR(\fIs\fR)\fR
.ad
.sp .6
.RS 4n
Return a string based on the string \fIs\fR. Each character in \fIs\fR that is
an upper-case letter specified to have a \fBtolower\fR mapping by the
\fBLC_CTYPE\fR category of the current locale is replaced in the returned
string by the lower-case letter specified by the mapping. Other characters in
\fIs\fR are unchanged in the returned string.
.RE

.sp
.ne 2
.na
\fB\fBtoupper\fR(\fIs\fR)\fR
.ad
.sp .6
.RS 4n
Return a string based on the string \fIs\fR. Each character in \fIs\fR that is
a lower-case letter specified to have a \fBtoupper\fR mapping by the
\fBLC_CTYPE\fR category of the current locale is replaced in the returned
string by the upper-case letter specified by the mapping. Other characters in
\fIs\fR are unchanged in the returned string.
.RE

.sp
.LP
All of the preceding functions that take \fIERE\fR as a parameter expect a
pattern or a string valued expression that is a regular expression as defined
below.

.SS "Input/Output and General Functions"
The input/output and general functions are:
.sp
.ne 2
.na
\fB\fBclose(\fR\fIexpression\fR)\fR
.ad
.RS 27n
Close the file or pipe opened by a \fBprint\fR or \fBprintf\fR statement or a
call to \fBgetline\fR with the same string-valued \fIexpression\fR. If the
close was successful, the function returns \fB0\fR; otherwise, it returns
non-zero.
.RE

.sp
.ne 2
.na
\fB\fBfflush(\fR\fIexpression\fR)\fR
.ad
.RS 27n
Flush any buffered output for the file or pipe opened by a \fBprint\fR or
\fBprintf\fR statement or a call to \fBgetline\fR with the same string-valued
\fIexpression\fR. If the flush was successful, the function returns \fB0\fR;
otherwise, it returns \fBEOF\fR. If no arguments or the empty string
(\fB""\fR) are given, then all open files will be flushed. (Note that
\fBfflush\fR is supported in \fB/usr/bin/awk\fR only.)
.RE

.sp
.ne 2
.na
\fB\fIexpression\fR|\fBgetline\fR[\fIvar\fR]\fR
.ad
.RS 27n
Read a record of input from a stream piped from the output of a command. The
stream is created if no stream is currently open with the value of
\fIexpression\fR as its command name. The stream created is equivalent to one
created by a call to the \fBpopen\fR function with the value of
\fIexpression\fR as the \fIcommand\fR argument and a value of \fBr\fR as the
\fImode\fR argument. As long as the stream remains open, subsequent calls in
which \fIexpression\fR evaluates to the same string value reads subsequent
records from the file. The stream remains open until the \fBclose\fR function
is called with an expression that evaluates to the same string value. At that
time, the stream is closed as if by a call to the \fBpclose\fR function. If
\fIvar\fR is missing, \fB$0\fR and \fBNF\fR is set. Otherwise, \fIvar\fR is
set.
.sp
The \fBgetline\fR operator can form ambiguous constructs when there are
operators that are not in parentheses (including concatenate) to the left of
the \fB|\fR (to the beginning of the expression containing \fBgetline\fR). In
the context of the \fB$\fR operator, \fB|\fR behaves as if it had a lower
precedence than \fB$\fR. The result of evaluating other operators is
unspecified, and all such uses of portable applications must be put in
parentheses properly.
.RE

.sp
.ne 2
.na
\fB\fBgetline\fR\fR
.ad
.RS 27n
Set \fB$0\fR to the next input record from the current input file. This form of
\fBgetline\fR sets the \fBNF\fR, \fBNR\fR, and \fBFNR\fR variables.
.RE

.sp
.ne 2
.na
\fB\fBgetline\fR \fIvar\fR\fR
.ad
.RS 27n
Set variable \fIvar\fR to the next input record from the current input file.
This form of \fBgetline\fR sets the \fBFNR\fR and \fBNR\fR variables.
.RE

.sp
.ne 2
.na
\fB\fBgetline\fR [\fIvar\fR] \fB<\fR \fIexpression\fR\fR
.ad
.RS 27n
Read the next record of input from a named file. The \fIexpression\fR is
evaluated to produce a string that is used as a full pathname. If the file of
that name is not currently open, it is opened. As long as the stream remains
open, subsequent calls in which \fIexpression\fR evaluates to the same string
value reads subsequent records from the file. The file remains open until the
\fBclose\fR function is called with an expression that evaluates to the same
string value. If \fIvar\fR is missing, \fB$0\fR and \fBNF\fR is set. Otherwise,
\fIvar\fR is set.
.sp
The \fBgetline\fR operator can form ambiguous constructs when there are binary
operators that are not in parentheses (including concatenate) to the right of
the \fB<\fR (up to the end of the expression containing the \fBgetline\fR). The
result of evaluating such a construct is unspecified, and all such uses of
portable applications must be put in parentheses properly.
.RE

.sp
.ne 2
.na
\fB\fBsystem\fR(\fIexpression\fR)\fR
.ad
.RS 27n
Execute the command given by \fIexpression\fR in a manner equivalent to the
\fBsystem\fR(3C) function and return the exit status of the command.
.RE

.sp
.LP
All forms of \fBgetline\fR return \fB1\fR for successful input, \fB0\fR for end
of file, and \fB\(mi1\fR for an error.
.sp
.LP
Where strings are used as the name of a file or pipeline, the strings must be
textually identical. The terminology ``same string value'' implies that
``equivalent strings'', even those that differ only by space characters,
represent different files.

.SS "User-defined Functions"
The \fBawk\fR language also provides user-defined functions. Such functions
can be defined as:
.sp
.in +2
.nf
\fBfunction\fR \fIname\fR(\fIargs\fR,\|.\|.\|.) { \fIstatements\fR }
.fi
.in -2

.sp
.LP
A function can be referred to anywhere in an \fBawk\fR program; in particular,
its use can precede its definition. The scope of a function is global.
.sp
.LP
Function arguments can be either scalars or arrays; the behavior is undefined
if an array name is passed as an argument that the function uses as a scalar,
or if a scalar expression is passed as an argument that the function uses as an
array. Function arguments are passed by value if scalar and by reference if
array name. Argument names are local to the function; all other variable names
are global. The same name is not used as both an argument name and as the name
of a function or a special \fBawk\fR variable. The same name must not be used
both as a variable name with global scope and as the name of a function. The
same name must not be used within the same scope both as a scalar variable and
as an array.
.sp
.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 are initialized with a string value of the null string and a
numeric value of zero, and the extra parameters that are used in the function
body as arrays are initialized as empty arrays. If more arguments are supplied
in a function call than are in the function definition, the behavior is
undefined.
.sp
.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 are
unchanged, except for array parameters passed by reference. The \fBreturn\fR
statement can be used to return a value. If a \fBreturn\fR statement appears
outside of a function definition, the behavior is undefined.
.sp
.LP
In the function definition, newline characters are optional before the opening
brace and after the closing brace. Function definitions can appear anywhere in
the program where a \fIpattern-action\fR pair is allowed.

.SH USAGE
The \fBindex\fR, \fBlength\fR, \fBmatch\fR, and \fBsubstr\fR functions should
not be confused with similar functions in the \fBISO C\fR standard; the
\fBawk\fR versions deal with characters, while the \fBISO C\fR standard deals
with bytes.
.sp
.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.
.sp
.LP
See \fBlargefile\fR(5) for the description of the behavior of \fBawk\fR when
encountering files greater than or equal to 2 Gbyte (2^31 bytes).

.SH EXAMPLES
The \fBawk\fR program specified in the command line is most easily specified
within single-quotes (for example, \fB\&'\fR\fIprogram\fR\fB\&'\fR) for
applications using \fBsh\fR, because \fBawk\fR programs commonly contain
characters that are special to the shell, including double-quotes. In the cases
where a \fBawk\fR 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
.in +2
.nf
awk '/'\e''/ { print "quote:", $0 }'
.fi
.in -2

.sp
.LP
prints all lines from the standard input containing a single-quote character,
prefixed with \fBquote:\fR.
.sp
.LP
The following are examples of simple \fBawk\fR programs:
.LP
\fBExample 1 \fRWrite to the standard output all input lines for which field 3
is greater than 5:
.sp
.in +2
.nf
\fB$3 > 5\fR
.fi
.in -2
.sp

.LP
\fBExample 2 \fRWrite every tenth line:
.sp
.in +2
.nf
\fB(NR % 10) == 0\fR
.fi
.in -2
.sp

.LP
\fBExample 3 \fRWrite any line with a substring matching the regular
expression:
.sp
.in +2
.nf
\fB/(G|D)(2[0-9][[:alpha:]]*)/\fR
.fi
.in -2
.sp

.LP
\fBExample 4 \fRPrint any line with a substring containing a G or D, followed
by a sequence of digits and characters:
.sp
.LP
This example uses character classes \fBdigit\fR and \fBalpha\fR to match
language-independent digit and alphabetic characters, respectively.

.sp
.in +2
.nf
\fB/(G|D)([[:digit:][:alpha:]]*)/\fR
.fi
.in -2
.sp

.LP
\fBExample 5 \fRWrite any line in which the second field matches the regular
expression and the fourth field does not:
.sp
.in +2
.nf
\fB$2 ~ /xyz/ && $4 !~ /xyz/\fR
.fi
.in -2
.sp

.LP
\fBExample 6 \fRWrite any line in which the second field contains a backslash:
.sp
.in +2
.nf
\fB$2 ~ /\e\e/\fR
.fi
.in -2
.sp

.LP
\fBExample 7 \fRWrite any line in which the second field contains a backslash
(alternate method):
.sp
.LP
Notice that backslash escapes are interpreted twice, once in lexical processing
of the string and once in processing the regular expression.

.sp
.in +2
.nf
\fB$2 ~ "\e\e\e\e"\fR
.fi
.in -2
.sp

.LP
\fBExample 8 \fRWrite the second to the last and the last field in each line,
separating the fields by a colon:
.sp
.in +2
.nf
\fB{OFS=":";print $(NF-1), $NF}\fR
.fi
.in -2
.sp

.LP
\fBExample 9 \fRWrite the line number and number of fields in each line:
.sp
.LP
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
.in +2
.nf
\fB{print NR ":" NF}\fR
.fi
.in -2
.sp

.LP
\fBExample 10 \fRWrite lines longer than 72 characters:
.sp
.in +2
.nf
\fB{length($0) > 72}\fR
.fi
.in -2
.sp

.LP
\fBExample 11 \fRWrite first two fields in opposite order separated by the OFS:
.sp
.in +2
.nf
\fB{ print $2, $1 }\fR
.fi
.in -2
.sp

.LP
\fBExample 12 \fRSame, with input fields separated by comma or space and tab
characters, or both:
.sp
.in +2
.nf
\fBBEGIN { FS = ",[\et]*|[\et]+" }
      { print $2, $1 }\fR
.fi
.in -2
.sp

.LP
\fBExample 13 \fRAdd up first column, print sum and average:
.sp
.in +2
.nf
\fB{s += $1 }
END {print "sum is ", s, " average is", s/NR}\fR
.fi
.in -2
.sp

.LP
\fBExample 14 \fRWrite fields in reverse order, one per line (many lines out
for each line in):
.sp
.in +2
.nf
\fB{ for (i = NF; i > 0; --i) print $i }\fR
.fi
.in -2
.sp

.LP
\fBExample 15 \fRWrite all lines between occurrences of the strings "start" and
"stop":
.sp
.in +2
.nf
\fB/start/, /stop/\fR
.fi
.in -2
.sp

.LP
\fBExample 16 \fRWrite all lines whose first field is different from the
previous one:
.sp
.in +2
.nf
\fB$1 != prev { print; prev = $1 }\fR
.fi
.in -2
.sp

.LP
\fBExample 17 \fRSimulate the echo command:
.sp
.in +2
.nf
\fBBEGIN  {
       for (i = 1; i < ARGC; ++i)
             printf "%s%s", ARGV[i], i==ARGC-1?"\en":""
       }\fR
.fi
.in -2
.sp

.LP
\fBExample 18 \fRWrite the path prefixes contained in the PATH environment
variable, one per line:
.sp
.in +2
.nf
\fBBEGIN  {
       n = split (ENVIRON["PATH"], path, ":")
       for (i = 1; i <= n; ++i)
              print path[i]
       }\fR
.fi
.in -2
.sp

.LP
\fBExample 19 \fRPrint the file "input", filling in page numbers starting at 5:
.sp
.LP
If there is a file named \fBinput\fR containing page headers of the form

.sp
.in +2
.nf
Page#
.fi
.in -2

.sp
.LP
and a file named \fBprogram\fR that contains

.sp
.in +2
.nf
/Page/{ $2 = n++; }
{ print }
.fi
.in -2

.sp
.LP
then the command line

.sp
.in +2
.nf
\fBawk -f program n=5 input\fR
.fi
.in -2
.sp

.sp
.LP
prints the file \fBinput\fR, filling in page numbers starting at 5.

.SH ENVIRONMENT VARIABLES
See \fBenviron\fR(5) for descriptions of the following environment variables
that affect execution: \fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and
\fBNLSPATH\fR.
.sp
.ne 2
.na
\fB\fBLC_NUMERIC\fR\fR
.ad
.RS 14n
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 \fBawk\fR
programs (including assignments in command-line arguments).
.RE

.SH EXIT STATUS
The following exit values are returned:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 6n
All input files were processed successfully.
.RE

.sp
.ne 2
.na
\fB\fB>0\fR\fR
.ad
.RS 6n
An error occurred.
.RE

.sp
.LP
The exit status can be altered within the program by using an \fBexit\fR
expression.

.SH SEE ALSO
\fBed\fR(1), \fBegrep\fR(1), \fBgrep\fR(1), \fBlex\fR(1), \fBoawk\fR(1),
\fBsed\fR(1), \fBpopen\fR(3C), \fBprintf\fR(3C), \fBsystem\fR(3C),
\fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5), \fBregex\fR(5),
\fBXPG4\fR(5)
.sp
.LP
Aho, A. V., B. W. Kernighan, and P. J. Weinberger, \fIThe AWK Programming
Language\fR, Addison-Wesley, 1988.

.SH DIAGNOSTICS
If any \fIfile\fR operand is specified and the named file cannot be accessed,
\fBawk\fR writes a diagnostic message to standard error and terminate without
any further action.
.sp
.LP
If the program specified by either the \fIprogram\fR operand or a
\fIprogfile\fR operand is not a valid \fBawk\fR program (as specified in
\fBEXTENDED DESCRIPTION\fR), the behavior is undefined.

.SH NOTES
Input white space is not preserved on output if fields are involved.
.sp
.LP
There are no explicit conversions between numbers and strings. To force an
expression to be treated as a number add 0 to it; to force it to be treated as
a string concatenate the null string (\fB""\fR) to it.