Windows PowerShell command on Get-command awk

Manual Pages for UNIX Operating System command usage for man awk

Utility Commands GAWK(1)

NAME

gawk - pattern scanning and processing language

SYNOPSIS

gawk [ POSIX or GNU style options ] -f program-file [ -- ]

file ...

gawk [ POSIX or GNU style options ] [ -- ] program-text file

...

pgawk [ POSIX or GNU style options ] -f program-file [ -- ]

file ...

pgawk [ POSIX or GNU style options ] [ -- ] program-text

file ...

DESCRIPTION

Gawk is the GNU Project's implementation of the AWK program-

ming language. It conforms to the definition of the language in the POSIX 1003.2 Command Language And Utilities Standard. This version in turn is based on the description in The AWK Programming Language, by Aho, Kernighan, and Weinberger, with the additional features found in the System

V Release 4 version of UNIX awk. Gawk also provides more

recent Bell Laboratories awk extensions, and a number of

GNU-specific extensions.

Pgawk is the profiling version of gawk. It is identical in

every way to gawk, except that programs run more slowly, and

it automatically produces an execution profile in the file

awkprof.out when done. See the --profile option, below.

The command line consists of options to gawk itself, the AWK

program text (if not supplied via the -f or --file options),

and values to be made available in the ARGC and ARGV pre-

defined AWK variables. OPTION FORMAT

Gawk options may be either traditional POSIX one letter

options, or GNU style long options. POSIX options start

with a single "-", while long options start with "--". Long

options are provided for both GNU-specific features and for

POSIX-mandated features.

Following the POSIX standard, gawk-specific options are sup-

plied via arguments to the -W option. Multiple -W options

may be supplied Each -W option has a corresponding long

option, as detailed below. Arguments to long options are

either joined with the option by an = sign, with no inter-

vening spaces, or they may be provided in the next command line argument. Long options may be abbreviated, as long as the abbreviation remains unique. Free Software FoundatLiaosnt change: June 26 2005 1 Utility Commands GAWK(1) OPTIONS

Gawk accepts the following options, listed alphabetically.

-F fs

--field-separator fs

Use fs for the input field separator (the value of the FS predefined variable).

-v var=val

--assign var=val

Assign the value val to the variable var, before execu-

tion of the program begins. Such variable values are available to the BEGIN block of an AWK program.

-f program-file

--file program-file

Read the AWK program source from the file program-file,

instead of from the first command line argument. Mul-

tiple -f (or --file) options may be used.

-mf NNN

-mr NNN

Set various memory limits to the value NNN. The f flag sets the maximum number of fields, and the r flag sets

the maximum record size. These two flags and the -m

option are from the Bell Laboratories research version

of UNIX awk. They are ignored by gawk, since gawk has

no pre-defined limits.

-W compat

-W traditional

--compat

--traditional

Run in compatibility mode. In compatibility mode, gawk

behaves identically to UNIX awk; none of the GNU-

specific extensions are recognized. The use of --trad-

itional is preferred over the other forms of this

option. See GNU EXTENSIONS, below, for more informa-

tion.

-W copyleft

-W copyright

--copyleft

--copyright

Print the short version of the GNU copyright informa-

tion message on the standard output and exit success-

fully.

-W dump-variables[=file]

--dump-variables[=file]

Print a sorted list of global variables, their types

and final values to file. If no file is provided, gawk

Free Software FoundatLiaosnt change: June 26 2005 2 Utility Commands GAWK(1)

uses a file named awkvars.out in the current directory.

Having a list of all the global variables is a good way to look for typographical errors in your programs. You would also use this option if you have a large program with a lot of functions, and you want to be sure that your functions don't inadvertently use global variables that you meant to be local. (This is a particularly easy mistake to make with simple variable names like i, j, and so on.)

-W exec file

--exec file

Similar to -f, however, this is option is the last one

processed. This should be used with #! scripts, par-

ticularly for CGI applications, to avoid passing in options or source code (!) on the command line from a

URL. This option disables command-line variable

assignments.

-W gen-po

--gen-po

Scan and parse the AWK program, and generate a GNU .po format file on standard output with entries for all localizable strings in the program. The program itself is not executed. See the GNU gettext distribution for more information on .po files.

-W help

-W usage

--help

--usage

Print a relatively short summary of the available options on the standard output. (Per the GNU Coding Standards, these options cause an immediate, successful exit.)

-W lint[=value]

--lint[=value]

Provide warnings about constructs that are dubious or

non-portable to other AWK implementations. With an

optional argument of fatal, lint warnings become fatal

errors. This may be drastic, but its use will cer-

tainly encourage the development of cleaner AWK pro-

grams. With an optional argument of invalid, only warnings about things that are actually invalid are issued. (This is not fully implemented yet.)

-W lint-old

--lint-old

Provide warnings about constructs that are not portable

to the original version of Unix awk.

Free Software FoundatLiaosnt change: June 26 2005 3 Utility Commands GAWK(1)

-W non-decimal-data

--non-decimal-data

Recognize octal and hexadecimal values in input data. Use this option with great caution!

-W posix

--posix

This turns on compatibility mode, with the following additional restrictions: +o \x escape sequences are not recognized. +o Only space and tab act as field separators when FS is set to a single space, newline does not. +o You cannot continue lines after ? and :. +o The synonym func for the keyword function is not recognized. +o The operators ** and **= cannot be used in place of ^ and ^=. +o The fflush() function is not available.

-W profile[=prof_file]

--profile[=prof_file]

Send profiling data to prof_file. The default is

awkprof.out. When run with gawk, the profile is just a

"pretty printed" version of the program. When run with

pgawk, the profile contains execution counts of each

statement in the program in the left margin and func-

tion call counts for each user-defined function.

-W re-interval

--re-interval

Enable the use of interval expressions in regular expression matching (see Regular Expressions, below). Interval expressions were not traditionally available in the AWK language. The POSIX standard added them, to

make awk and egrep consistent with each other. How-

ever, their use is likely to break old AWK programs, so

gawk only provides them if they are requested with this

option, or when --posix is specified.

-W source program-text

--source program-text

Use program-text as AWK program source code. This

option allows the easy intermixing of library functions

(used via the -f and --file options) with source code

entered on the command line. It is intended primarily for medium to large AWK programs used in shell scripts. Free Software FoundatLiaosnt change: June 26 2005 4 Utility Commands GAWK(1)

-W version

--version

Print version information for this particular copy of

gawk on the standard output. This is useful mainly for

knowing if the current copy of gawk on your system is

up to date with respect to whatever the Free Software Foundation is distributing. This is also useful when reporting bugs. (Per the GNU Coding Standards, these options cause an immediate, successful exit.)

-- Signal the end of options. This is useful to allow

further arguments to the AWK program itself to start

with a "-". This is mainly for consistency with the

argument parsing convention used by most other POSIX programs. In compatibility mode, any other options are flagged as invalid, but are otherwise ignored. In normal operation, as long as program text has been supplied, unknown options are

passed on to the AWK program in the ARGV array for process-

ing. This is particularly useful for running AWK programs

via the "#!" executable interpreter mechanism.

AWK PROGRAM EXECUTION

An AWK program consists of a sequence of pattern-action

statements and optional function definitions. pattern { action statements } function name(parameter list) { statements }

Gawk first reads the program source from the program-file(s)

if specified, from arguments to --source, or from the first

non-option argument on the command line. The -f and

--source options may be used multiple times on the command

line. Gawk reads the program text as if all the program-

files and command line source texts had been concatenated together. This is useful for building libraries of AWK functions, without having to include them in each new AWK program that uses them. It also provides the ability to mix library functions with command line programs. The environment variable AWKPATH specifies a search path to

use when finding source files named with the -f option. If

this variable does not exist, the default path is

".:/usr/local/share/awk". (The actual directory may vary,

depending upon how gawk was built and installed.) If a file

name given to the -f option contains a "/" character, no

path search is performed.

Gawk executes AWK programs in the following order. First,

all variable assignments specified via the -v option are

performed. Next, gawk compiles the program into an internal

form. Then, gawk executes the code in the BEGIN block(s)

(if any), and then proceeds to read each file named in the ARGV array. If there are no files named on the command

line, gawk reads the standard input.

If a filename on the command line has the form var=val it is treated as a variable assignment. The variable var will be Free Software FoundatLiaosnt change: June 26 2005 5 Utility Commands GAWK(1) assigned the value val. (This happens after any BEGIN block(s) have been run.) Command line variable assignment

is most useful for dynamically assigning values to the vari-

ables AWK uses to control how input is broken into fields and records. It is also useful for controlling state if multiple passes are needed over a single data file. If the value of a particular element of ARGV is empty (""),

gawk skips over it.

For each record in the input, gawk tests to see if it

matches any pattern in the AWK program. For each pattern that the record matches, the associated action is executed.

The patterns are tested in the order they occur in the pro-

gram.

Finally, after all the input is exhausted, gawk executes the

code in the END block(s) (if any). VARIABLES, RECORDS AND FIELDS AWK variables are dynamic; they come into existence when

they are first used. Their values are either floating-point

numbers or strings, or both, depending upon how they are

used. AWK also has one dimensional arrays; arrays with mul-

tiple dimensions may be simulated. Several pre-defined

variables are set as a program runs; these will be described as needed and summarized below. Records Normally, records are separated by newline characters. You can control how records are separated by assigning values to

the built-in variable RS. If RS is any single character,

that character separates records. Otherwise, RS is a regu-

lar expression. Text in the input that matches this regular expression separates the record. However, in compatibility mode, only the first character of its string value is used for separating records. If RS is set to the null string, then records are separated by blank lines. When RS is set to the null string, the newline character always acts as a field separator, in addition to whatever value FS may have. Fields

As each input record is read, gawk splits the record into

fields, using the value of the FS variable as the field separator. If FS is a single character, fields are separated by that character. If FS is the null string, then

each individual character becomes a separate field. Other-

wise, FS is expected to be a full regular expression. In the special case that FS is a single space, fields are separated by runs of spaces and/or tabs and/or newlines.

(But see the discussion of --posix, below). NOTE: The value

of IGNORECASE (see below) also affects how fields are split when FS is a regular expression, and how records are separated when RS is a regular expression. If the FIELDWIDTHS variable is set to a space separated list of numbers, each field is expected to have fixed width, and

gawk splits up the record using the specified widths. The

value of FS is ignored. Assigning a new value to FS Free Software FoundatLiaosnt change: June 26 2005 6 Utility Commands GAWK(1) overrides the use of FIELDWIDTHS, and restores the default behavior. Each field in the input record may be referenced by its

position, $1, $2, and so on. $0 is the whole record.

Fields need not be referenced by constants: n = 5

print $n

prints the fifth field in the input record. The variable NF is set to the total number of fields in the input record.

References to non-existent fields (i.e. fields after $NF)

produce the null-string. However, assigning to a non-

existent field (e.g., $(NF+2) = 5) increases the value of

NF, creates any intervening fields with the null string as

their value, and causes the value of $0 to be recomputed,

with the fields being separated by the value of OFS. Refer-

ences to negative numbered fields cause a fatal error. Decrementing NF causes the values of fields past the new

value to be lost, and the value of $0 to be recomputed, with

the fields being separated by the value of OFS. Assigning a value to an existing field causes the whole

record to be rebuilt when $0 is referenced. Similarly,

assigning a value to $0 causes the record to be resplit,

creating new values for the fields.

Built-in Variables

Gawk's built-in variables are:

ARGC The number of command line arguments (does not

include options to gawk, or the program source).

ARGIND The index in ARGV of the current file being pro-

cessed. ARGV Array of command line arguments. The array is

indexed from 0 to ARGC - 1. Dynamically chang-

ing the contents of ARGV can control the files used for data.

BINMODE On non-POSIX systems, specifies use of "binary"

mode for all file I/O. Numeric values of 1, 2, or 3, specify that input files, output files, or

all files, respectively, should use binary I/O. String values of "r", or "w" specify that input files, or output files, respectively, should use

binary I/O. String values of "rw" or "wr"

specify that all files should use binary I/O. Any other string value is treated as "rw", but generates a warning message.

CONVFMT The conversion format for numbers, "%.6g", by

default. ENVIRON An array containing the values of the current environment. The array is indexed by the environment variables, each element being the value of that variable (e.g., ENVIRON["HOME"] might be /home/arnold). Changing this array does not affect the environment seen by programs Free Software FoundatLiaosnt change: June 26 2005 7 Utility Commands GAWK(1)

which gawk spawns via redirection or the sys-

tem() function.

ERRNO If a system error occurs either doing a redirec-

tion for getline, during a read for getline, or during a close(), then ERRNO will contain a

string describing the error. The value is sub-

ject to translation in non-English locales.

FIELDWIDTHS A white-space separated list of fieldwidths.

When set, gawk parses the input into fields of

fixed width, instead of using the value of the FS variable as the field separator.

FILENAME The name of the current input file. If no files

are specified on the command line, the value of

FILENAME is "-". However, FILENAME is undefined

inside the BEGIN block (unless set by getline). FNR The input record number in the current input file. FS The input field separator, a space by default. See Fields, above.

IGNORECASE Controls the case-sensitivity of all regular

expression and string operations. If IGNORECASE

has a non-zero value, then string comparisons

and pattern matching in rules, field splitting with FS, record separating with RS, regular

expression matching with ~ and !~, and the gen-

sub(), gsub(), index(), match(), split(), and

sub() built-in functions all ignore case when

doing regular expression operations. NOTE: Array subscripting is not affected. However, the asort() and asorti() functions are affected. Thus, if IGNORECASE is not equal to zero, /aB/ matches all of the strings "ab", "aB", "Ab", and "AB". As with all AWK variables, the initial value of IGNORECASE is zero, so all regular expression and string operations are normally

case-sensitive. Under Unix, the full ISO 8859-1

Latin-1 character set is used when ignoring

case. As of gawk 3.1.4, the case equivalencies

are fully locale-aware, based on the C

facilities such as isalpha(), and tolupper().

LINT Provides dynamic control of the --lint option

from within an AWK program. When true, gawk

prints lint warnings. When false, it does not. When assigned the string value "fatal", lint warnings become fatal errors, exactly like

--lint=fatal. Any other true value just prints

warnings. NF The number of fields in the current input record. NR The total number of input records seen so far.

OFMT The output format for numbers, "%.6g", by

default. Free Software FoundatLiaosnt change: June 26 2005 8 Utility Commands GAWK(1) OFS The output field separator, a space by default.

ORS The output record separator, by default a new-

line. PROCINFO The elements of this array provide access to information about the running AWK program. On some systems, there may be elements in the array, "group1" through "groupn" for some n, which is the number of supplementary groups that the process has. Use the in operator to test for these elements. The following elements are guaranteed to be available: PROCINFO["egid"] the value of the getegid(2) system call. PROCINFO["euid"] the value of the geteuid(2) system call. PROCINFO["FS"] "FS" if field splitting with FS is in effect, or

"FIELDWIDTHS" if field split-

ting with FIELDWIDTHS is in effect. PROCINFO["gid"] the value of the getgid(2) system call. PROCINFO["pgrpid"] the process group ID of the current process. PROCINFO["pid"] the process ID of the current process. PROCINFO["ppid"] the parent process ID of the current process. PROCINFO["uid"] the value of the getuid(2) system call. PROCINFO["version"]

The version of gawk. This is

available from version 3.1.4 and later.

RS The input record separator, by default a new-

line.

RT The record terminator. Gawk sets RT to the

input text that matched the character or regular expression specified by RS. RSTART The index of the first character matched by match(); 0 if no match. (This implies that character indices start at one.)

RLENGTH The length of the string matched by match(); -1

if no match.

SUBSEP The character used to separate multiple sub-

scripts in array elements, by default "\034". TEXTDOMAIN The text domain of the AWK program; used to find the localized translations for the program's strings. Arrays Arrays are subscripted with an expression between square brackets ([ and ]). If the expression is an expression list Free Software FoundatLiaosnt change: June 26 2005 9 Utility Commands GAWK(1)

(expr, expr ...) then the array subscript is a string con-

sisting of the concatenation of the (string) value of each expression, separated by the value of the SUBSEP variable. This facility is used to simulate multiply dimensioned arrays. For example: i = "A"; j = "B"; k = "C" x[i, j, k] = "hello, world\n" assigns the string "hello, world\n" to the element of the array x which is indexed by the string "A\034B\034C". All arrays in AWK are associative, i.e. indexed by string values.

The special operator in may be used in an if or while state-

ment to see if an array has an index consisting of a partic-

ular value. if (val in array) print array[val] If the array has multiple subscripts, use (i, j) in array. The in construct may also be used in a for loop to iterate over all the elements of an array. An element may be deleted from an array using the delete statement. The delete statement may also be used to delete the entire contents of an array, just by specifying the array name without a subscript. Variable Typing And Conversion Variables and fields may be (floating point) numbers, or

strings, or both. How the value of a variable is inter-

preted depends upon its context. If used in a numeric expression, it will be treated as a number, if used as a string it will be treated as a string. To force a variable to be treated as a number, add 0 to it; to force it to be treated as a string, concatenate it with the null string. When a string must be converted to a number, the conversion is accomplished using strtod(3). A number is converted to a string by using the value of CONVFMT as a format string for sprintf(3), with the numeric value of the variable as the argument. However, even though all numbers in AWK are

floating-point, integral values are always converted as

integers. Thus, given

CONVFMT = "%2.2f"

a = 12 b = a "" the variable b has a string value of "12" and not "12.00".

Gawk performs comparisons as follows: If two variables are

numeric, they are compared numerically. If one value is numeric and the other has a string value that is a "numeric

string," then comparisons are also done numerically. Other-

wise, the numeric value is converted to a string and a string comparison is performed. Two strings are compared, of course, as strings. Note that the POSIX standard applies the concept of "numeric string" everywhere, even to string

constants. However, this is clearly incorrect, and gawk

Free Software FoundatLiaosnt change: June 26 2005 10 Utility Commands GAWK(1) does not do this. (Fortunately, this is fixed in the next version of the standard.) Note that string constants, such as "57", are not numeric strings, they are string constants. The idea of "numeric

string" only applies to fields, getline input, FILENAME,

ARGV elements, ENVIRON elements and the elements of an array created by split() that are numeric strings. The basic idea is that user input, and only user input, that looks numeric, should be treated that way. Uninitialized variables have the numeric value 0 and the string value "" (the null, or empty, string). Octal and Hexadecimal Constants

Starting with version 3.1 of gawk , you may use C-style

octal and hexadecimal constants in your AWK program source code. For example, the octal value 011 is equal to decimal 9, and the hexadecimal value 0x11 is equal to decimal 17. String Constants String constants in AWK are sequences of characters enclosed between double quotes ("). Within strings, certain escape sequences are recognized, as in C. These are: \\ A literal backslash. \a The "alert" character; usually the ASCII BEL character. \b backspace.

\f form-feed.

\n newline. \r carriage return. \t horizontal tab. \v vertical tab. \xhex digits The character represented by the string of hexadecimal digits following the \x. As in ANSI C, all following hexadecimal digits are considered part of the escape sequence. (This feature should tell us something about language design by committee.) E.g., "\x1B" is the ASCII ESC (escape) character.

\ddd The character represented by the 1-, 2-, or 3-digit

sequence of octal digits. E.g., "\033" is the ASCII ESC (escape) character. \c The literal character c.

The escape sequences may also be used inside constant regu-

lar expressions (e.g., /[ \t\f\n\r\v]/ matches whitespace characters). In compatibility mode, the characters represented by octal and hexadecimal escape sequences are treated literally when used in regular expression constants. Thus, /a\52b/ is equivalent to /a\*b/. PATTERNS AND ACTIONS

AWK is a line-oriented language. The pattern comes first,

and then the action. Action statements are enclosed in { and }. Either the pattern may be missing, or the action may be missing, but, of course, not both. If the pattern is missing, the action is executed for every single record of Free Software FoundatLiaosnt change: June 26 2005 11 Utility Commands GAWK(1) input. A missing action is equivalent to { print } which prints the entire record.

Comments begin with the "#" character, and continue until

the end of the line. Blank lines may be used to separate

statements. Normally, a statement ends with a newline, how-

ever, this is not the case for lines ending in a ",", {, ?, :, &&, or ||. Lines ending in do or else also have their statements automatically continued on the following line. In other cases, a line can be continued by ending it with a "\", in which case the newline will be ignored. Multiple statements may be put on one line by separating them with a ";". This applies to both the statements within

the action part of a pattern-action pair (the usual case),

and to the pattern-action statements themselves.

Patterns AWK patterns may be one of the following: BEGIN END /regular expression/ relational expression pattern && pattern pattern || pattern pattern ? pattern : pattern (pattern) ! pattern pattern1, pattern2 BEGIN and END are two special kinds of patterns which are not tested against the input. The action parts of all BEGIN

patterns are merged as if all the statements had been writ-

ten in a single BEGIN block. They are executed before any of the input is read. Similarly, all the END blocks are merged, and executed when all the input is exhausted (or when an exit statement is executed). BEGIN and END patterns

cannot be combined with other patterns in pattern expres-

sions. BEGIN and END patterns cannot have missing action parts. For /regular expression/ patterns, the associated statement is executed for each input record that matches the regular expression. Regular expressions are the same as those in egrep(1), and are summarized below. A relational expression may use any of the operators defined below in the section on actions. These generally test whether certain fields match certain regular expressions. The &&, ||, and ! operators are logical AND, logical OR, and

logical NOT, respectively, as in C. They do short-circuit

evaluation, also as in C, and are used for combining more primitive pattern expressions. As in most languages, parentheses may be used to change the order of evaluation. The ?: operator is like the same operator in C. If the first pattern is true then the pattern used for testing is the second pattern, otherwise it is the third. Only one of Free Software FoundatLiaosnt change: June 26 2005 12 Utility Commands GAWK(1) the second and third patterns is evaluated. The pattern1, pattern2 form of an expression is called a range pattern. It matches all input records starting with a record that matches pattern1, and continuing until a record that matches pattern2, inclusive. It does not combine with any other sort of pattern expression. Regular Expressions Regular expressions are the extended kind found in egrep. They are composed of characters as follows:

c matches the non-metacharacter c.

\c matches the literal character c. . matches any character including newline. ^ matches the beginning of a string.

$ matches the end of a string.

[abc...] character list, matches any of the characters abc.... [^abc...] negated character list, matches any character except abc.... r1|r2 alternation: matches either r1 or r2. r1r2 concatenation: matches r1, and then r2. r+ matches one or more r's. r* matches zero or more r's. r? matches zero or one r's. (r) grouping: matches r. r{n} r{n,}

r{n,m} One or two numbers inside braces denote an inter-

val expression. If there is one number in the braces, the preceding regular expression r is repeated n times. If there are two numbers separated by a comma, r is repeated n to m times. If there is one number followed by a comma, then r is repeated at least n times. Interval expressions are only available if either

--posix or --re-interval is specified on the com-

mand line. \y matches the empty string at either the beginning or the end of a word. \B matches the empty string within a word. \< matches the empty string at the beginning of a word. \> matches the empty string at the end of a word.

\w matches any word-constituent character (letter,

digit, or underscore).

\W matches any character that is not word-

constituent. Free Software FoundatLiaosnt change: June 26 2005 13 Utility Commands GAWK(1) \` matches the empty string at the beginning of a buffer (string). \' matches the empty string at the end of a buffer. The escape sequences that are valid in string constants (see below) are also valid in regular expressions. Character classes are a new feature introduced in the POSIX standard. A character class is a special notation for

describing lists of characters that have a specific attri-

bute, but where the actual characters themselves can vary

from country to country and/or from character set to charac-

ter set. For example, the notion of what is an alphabetic character differs in the USA and in France. A character class is only valid in a regular expression inside the brackets of a character list. Character classes consist of [:, a keyword denoting the class, and :]. The character classes defined by the POSIX standard are: [:alnum:] Alphanumeric characters. [:alpha:] Alphabetic characters. [:blank:] Space or tab characters. [:cntrl:] Control characters. [:digit:] Numeric characters. [:graph:] Characters that are both printable and visible. (A space is printable, but not visible, while an a is both.)

[:lower:] Lower-case alphabetic characters.

[:print:] Printable characters (characters that are not control characters.) [:punct:] Punctuation characters (characters that are not letter, digits, control characters, or space characters). [:space:] Space characters (such as space, tab, and formfeed, to name a few).

[:upper:] Upper-case alphabetic characters.

[:xdigit:] Characters that are hexadecimal digits. Free Software FoundatLiaosnt change: June 26 2005 14 Utility Commands GAWK(1) For example, before the POSIX standard, to match alphanumeric characters, you would have had to write

/[A-Za-z0-9]/. If your character set had other alphabetic

characters in it, this would not match them, and if your character set collated differently from ASCII, this might not even match the ASCII alphanumeric characters. With the POSIX character classes, you can write /[[:alnum:]]/, and this matches the alphabetic and numeric characters in your character set. Two additional special sequences can appear in character

lists. These apply to non-ASCII character sets, which can

have single symbols (called collating elements) that are represented with more than one character, as well as several characters that are equivalent for collating, or sorting,

purposes. (E.g., in French, a plain "e" and a grave-

accented e` are equivalent.) Collating Symbols

A collating symbol is a multi-character collating ele-

ment enclosed in [. and .]. For example, if ch is a

collating element, then [[.ch.]] is a regular expres-

sion that matches this collating element, while [ch] is a regular expression that matches either c or h. Equivalence Classes

An equivalence class is a locale-specific name for a

list of characters that are equivalent. The name is enclosed in [= and =]. For example, the name e might be used to represent all of "e," "e'," and "e`." In this case, [[=e=]] is a regular expression that matches any of e, e', or e`.

These features are very valuable in non-English speaking

locales. The library functions that gawk uses for regular

expression matching currently only recognize POSIX character classes; they do not recognize collating symbols or equivalence classes. The \y, \B, \<, \>, \w, \W, \`, and \' operators are

specific to gawk; they are extensions based on facilities in

the GNU regular expression libraries.

The various command line options control how gawk interprets

characters in regular expressions. No options

In the default case, gawk provide all the facilities of

POSIX regular expressions and the GNU regular expres-

sion operators described above. However, interval expressions are not supported. Free Software FoundatLiaosnt change: June 26 2005 15 Utility Commands GAWK(1)

--posix

Only POSIX regular expressions are supported, the GNU operators are not special. (E.g., \w matches a literal w). Interval expressions are allowed.

--traditional

Traditional Unix awk regular expressions are matched.

The GNU operators are not special, interval expressions are not available, and neither are the POSIX character classes ([[:alnum:]] and so on). Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regular expression metacharacters.

--re-interval

Allow interval expressions in regular expressions, even

if --traditional has been provided.

Actions Action statements are enclosed in braces, { and }. Action statements consist of the usual assignment, conditional, and looping statements found in most languages. The operators, control statements, and input/output statements available are patterned after those in C. Operators The operators in AWK, in order of decreasing precedence, are (...) Grouping

$ Field reference.

++ -- Increment and decrement, both prefix and post-

fix. ^ Exponentiation (** may also be used, and **= for the assignment operator).

+ - ! Unary plus, unary minus, and logical negation.

* / % Multiplication, division, and modulus.

+ - Addition and subtraction.

space String concatenation. < > <= >= != == The regular relational operators. ~ !~ Regular expression match, negated match. NOTE: Do not use a constant regular expression (/foo/) Free Software FoundatLiaosnt change: June 26 2005 16 Utility Commands GAWK(1)

on the left-hand side of a ~ or !~. Only use

one on the right-hand side. The expression

/foo/ ~ exp has the same meaning as (($0 ~

/foo/) ~ exp). This is usually not what was intended. in Array membership. && Logical AND. || Logical OR. ?: The C conditional expression. This has the form expr1 ? expr2 : expr3. If expr1 is true, the value of the expression is expr2, otherwise it is expr3. Only one of expr2 and expr3 is evaluated.

= += -=

*= /= %= ^= Assignment. Both absolute assignment (var =

value) and operator-assignment (the other forms)

are supported. Control Statements The control statements are as follows: if (condition) statement [ else statement ] while (condition) statement do statement while (condition) for (expr1; expr2; expr3) statement for (var in array) statement break continue delete array[index] delete array exit [ expression ] { statements }

I/O Statements The input/output statements are as follows:

close(file [, how]) Close file, pipe or co-process. The

optional how should only be used when

closing one end of a two-way pipe to a

co-process. It must be a string

value, either "to" or "from".

getline Set $0 from next input record; set NF,

NR, FNR.

getline NF. Free Software FoundatLiaosnt change: June 26 2005 17 Utility Commands GAWK(1) getline var Set var from next input record; set NR, FNR. getline var

into $0 or var, as above.

command |& getline [var]

Run command as a co-process piping the

output either into $0 or var, as

above. Co-processes are a gawk exten-

sion. next Stop processing the current input record. The next input record is read and processing starts over with the first pattern in the AWK program. If the end of the input data is reached,

the END block(s), if any, are exe-

cuted. nextfile Stop processing the current input file. The next input record read comes from the next input file.

FILENAME and ARGIND are updated, FNR

is reset to 1, and processing starts over with the first pattern in the AWK program. If the end of the input data is reached, the END block(s), if any, are executed. print Prints the current record. The output record is terminated with the value of the ORS variable.

print expr-list Prints expressions. Each expression

is separated by the value of the OFS

variable. The output record is ter-

minated with the value of the ORS variable.

print expr-list >file Prints expressions on file. Each

expression is separated by the value of the OFS variable. The output record is terminated with the value of the ORS variable.

printf fmt, expr-list Format and print.

printf fmt, expr-list >file

Free Software FoundatLiaosnt change: June 26 2005 18 Utility Commands GAWK(1) Format and print on file.

system(cmd-line) Execute the command cmd-line, and

return the exit status. (This may not

be available on non-POSIX systems.)

fflush([file]) Flush any buffers associated with the open output file or pipe file. If file is missing, then standard output is flushed. If file is the null string, then all open output files and pipes have their buffers flushed. Additional output redirections are allowed for print and printf. print ... >> file appends output to the file. print ... | command writes on a pipe. print ... |& command

sends data to a co-process.

The getline command returns 0 on end of file and -1 on an

error. Upon an error, ERRNO contains a string describing the problem.

NOTE: If using a pipe or co-process to getline, or from

print or printf within a loop, you must use close() to

create new instances of the command. AWK does not automati-

cally close pipes or co-processes when they return EOF.

The printf Statement

The AWK versions of the printf statement and sprintf() func-

tion (see below) accept the following conversion specifica-

tion formats:

%c An ASCII character. If the argument used for %c is

numeric, it is treated as a character and printed. Otherwise, the argument is assumed to be a string, and the only first character of that string is printed.

%d, %i A decimal number (the integer part).

%e , %E

A floating point number of the form

[-]d.dddddde[+-]dd. The %E format uses E instead of

e. Free Software FoundatLiaosnt change: June 26 2005 19 Utility Commands GAWK(1)

%f A floating point number of the form [-]ddd.dddddd.

%g , %G

Use %e or %f conversion, whichever is shorter, with

nonsignificant zeros suppressed. The %G format uses

%E instead of %e.

%o An unsigned octal number (also an integer).

%u An unsigned decimal number (again, an integer).

%s A character string.

%x , %X

An unsigned hexadecimal number (an integer). The %X

format uses ABCDEF instead of abcdef.

%% A single % character; no argument is converted.

NOTE: When using the integer format-control letters for

values that are outside the range of a C long integer, gawk

switches to the %g format specifier. If --lint is provided

on the command line gawk warns about this. Other versions

of awk may print invalid values or do something else

entirely.

Optional, additional parameters may lie between the % and

the control letter:

count$

Use the count'th argument at this point in the format-

ting. This is called a positional specifier and is intended primarily for use in translated versions of

format strings, not in the original text of an AWK pro-

gram. It is a gawk extension.

- The expression should be left-justified within its

field. space For numeric conversions, prefix positive values with a space, and negative values with a minus sign. + The plus sign, used before the width modifier (see below), says to always supply a sign for numeric

conversions, even if the data to be formatted is posi-

tive. The + overrides the space modifier.

# Use an "alternate form" for certain control letters.

For %o, supply a leading zero. For %x, and %X, supply

a leading 0x or 0X for a nonzero result. For %e, %E,

and %f, the result always contains a decimal point.

Free Software FoundatLiaosnt change: June 26 2005 20 Utility Commands GAWK(1)

For %g, and %G, trailing zeros are not removed from the

result.

0 A leading 0 (zero) acts as a flag, that indicates out-

put should be padded with zeroes instead of spaces.

This applies even to non-numeric output formats. This

flag only has an effect when the field width is wider than the value to be printed. width The field should be padded to this width. The field is normally padded with spaces. If the 0 flag has been used, it is padded with zeroes. .prec A number that specifies the precision to use when

printing. For the %e, %E, and %f formats, this speci-

fies the number of digits you want printed to the right

of the decimal point. For the %g, and %G formats, it

specifies the maximum number of significant digits.

For the %d, %o, %i, %u, %x, and %X formats, it speci-

fies the minimum number of digits to print. For %s, it

specifies the maximum number of characters from the string that should be printed. The dynamic width and prec capabilities of the ANSI C printf() routines are supported. A * in place of either the width or prec specifications causes their values to be taken from the argument list to printf or sprintf(). To use a

positional specifier with a dynamic width or precision, sup-

ply the count$ after the * in the format string. For exam-

ple, "%3$*2$.*1$s".

Special File Names

When doing I/O redirection from either print or printf into

a file, or via getline from a file, gawk recognizes certain

special filenames internally. These filenames allow access

to open file descriptors inherited from gawk's parent pro-

cess (usually the shell). These file names may also be used on the command line to name data files. The filenames are: /dev/stdin The standard input. /dev/stdout The standard output. /dev/stderr The standard error output.

/dev/fd/n The file associated with the open file descrip-

tor n.

These are particularly useful for error messages. For exam-

ple: Free Software FoundatLiaosnt change: June 26 2005 21 Utility Commands GAWK(1) print "You blew it!" > "/dev/stderr" whereas you would otherwise have to use print "You blew it!" | "cat 1>&2"

The following special filenames may be used with the |& co-

process operator for creating TCP/IP network connections.

/inet/tcp/lport/rhost/rport File for TCP/IP connection on local port lport to remote host rhost on remote port rport. Use a port of 0 to have the system pick a port.

/inet/udp/lport/rhost/rport Similar, but use UDP/IP instead

of TCP/IP. /inet/raw/lport/rhost/rport Reserved for future use. Other special filenames provide access to information about

the running gawk process. These filenames are now obsolete.

Use the PROCINFO array to obtain the information they pro-

vide. The filenames are: /dev/pid Reading this file returns the process ID of the current process, in decimal, terminated with a newline. /dev/ppid Reading this file returns the parent process ID of the current process, in decimal, terminated with a newline. /dev/pgrpid Reading this file returns the process group ID of the current process, in decimal, terminated with a newline.

/dev/user Reading this file returns a single record ter-

minated with a newline. The fields are

separated with spaces. $1 is the value of the

getuid(2) system call, $2 is the value of the

geteuid(2) system call, $3 is the value of the

getgid(2) system call, and $4 is the value of

the getegid(2) system call. If there are any additional fields, they are the group IDs returned by getgroups(2). Multiple groups may not be supported on all systems. Numeric Functions

AWK has the following built-in arithmetic functions:

Free Software FoundatLiaosnt change: June 26 2005 22 Utility Commands GAWK(1) atan2(y, x) Returns the arctangent of y/x in radians.

cos(expr) Returns the cosine of expr, which is in radi-

ans. exp(expr) The exponential function. int(expr) Truncates to integer. log(expr) The natural logarithm function. rand() Returns a random number N, between 0 and 1, such that 0 < N < 1. sin(expr) Returns the sine of expr, which is in radians. sqrt(expr) The square root function. srand([expr]) Uses expr as a new seed for the random number generator. If no expr is provided, the time

of day is used. The return value is the pre-

vious seed for the random number generator. String Functions

Gawk has the following built-in string functions:

asort(s [, d]) Returns the number of elements in the source array s. The contents of

s are sorted using gawk's normal

rules for comparing values, and the indexes of the sorted values of s are replaced with sequential integers starting with 1. If the optional destination array d is

specified, then s is first dupli-

cated into d, and then d is sorted, leaving the indexes of the source array s unchanged. asorti(s [, d]) Returns the number of elements in the source array s. The behavior is the same as that of asort(), except that the array indices are used for sorting, not the array values. When

done, the array is indexed numeri-

cally, and the values are those of the original indices. The original values are lost; thus provide a second array if you wish to preserve the original. gensub(r, s, h [, t]) Search the target string t for Free Software FoundatLiaosnt change: June 26 2005 23 Utility Commands GAWK(1) matches of the regular expression r. If h is a string beginning with g or G, then replace all matches of r with s. Otherwise, h is a number indicating which match of r to

replace. If t is not supplied, $0

is used instead. Within the replacement text s, the sequence \n, where n is a digit from 1 to 9, may be used to indicate just the text that matched the n'th parenthesized subexpression. The sequence \0 represents the entire matched text, as does the character &. Unlike sub() and gsub(), the modified string is returned as the result of

the function, and the original tar-

get string is not changed.

gsub(r, s [, t]) For each substring matching the reg-

ular expression r in the string t, substitute the string s, and return the number of substitutions. If t

is not supplied, use $0. An & in

the replacement text is replaced with the text that was actually matched. Use \& to get a literal &. (This must be typed as "\\&"; see GAWK: Effective AWK Programming for a fuller discussion of the rules for

&'s and backslashes in the replace-

ment text of sub(), gsub(), and gen-

sub().) index(s, t) Returns the index of the string t in the string s, or 0 if t is not

present. (This implies that charac-

ter indices start at one.) length([s]) Returns the length of the string s,

or the length of $0 if s is not sup-

plied. Starting with version 3.1.5,

as a non-standard extension, with an

array argument, length() returns the number of elements in the array. match(s, r [, a]) Returns the position in s where the regular expression r occurs, or 0 if r is not present, and sets the values of RSTART and RLENGTH. Note that the argument order is the same as for the ~ operator: str ~ re. Free Software FoundatLiaosnt change: June 26 2005 24 Utility Commands GAWK(1) If array a is provided, a is cleared and then elements 1 through n are filled with the portions of s that match the corresponding parenthesized subexpression in r. The 0'th element of a contains the portion of s matched by the entire regular expression r. Subscripts a[n, "start"], and a[n, "length"] provide the starting index in the string and length respectively, of each matching substring. split(s, a [, r]) Splits the string s into the array a on the regular expression r, and returns the number of fields. If r is omitted, FS is used instead. The array a is cleared first. Splitting

behaves identically to field split-

ting, described above.

sprintf(fmt, expr-list) Prints expr-list according to fmt,

and returns the resulting string. strtonum(str) Examines str, and returns its numeric value. If str begins with a leading 0, strtonum() assumes that str is an octal number. If str begins with a leading 0x or 0X, strtonum() assumes that str is a hexadecimal number. sub(r, s [, t]) Just like gsub(), but only the first matching substring is replaced.

substr(s, i [, n]) Returns the at most n-character sub-

string of s starting at i. If n is omitted, the rest of s is used. tolower(str) Returns a copy of the string str,

with all the upper-case characters

in str translated to their

corresponding lower-case counter-

parts. Non-alphabetic characters

are left unchanged. toupper(str) Returns a copy of the string str,

with all the lower-case characters

in str translated to their

corresponding upper-case counter-

parts. Non-alphabetic characters

are left unchanged. Free Software FoundatLiaosnt change: June 26 2005 25 Utility Commands GAWK(1) Time Functions Since one of the primary uses of AWK programs is processing

log files that contain time stamp information, gawk provides

the following functions for obtaining time stamps and for-

matting them. mktime(datespec) Turns datespec into a time stamp of the same form as returned by systime(). The datespec is a string of the form YYYY MM DD HH MM SS[ DST]. The contents of the string are six or seven numbers representing respectively the full year including century, the month from 1 to 12, the day of the month from 1 to 31, the hour of the day from 0 to 23, the minute from 0 to 59, and the second from 0 to 60, and an optional daylight saving flag. The values of these numbers need not be within the

ranges specified; for example, an hour of -1 means

1 hour before midnight. The origin-zero Gregorian

calendar is assumed, with year 0 preceding year 1

and year -1 preceding year 0. The time is assumed

to be in the local timezone. If the daylight sav-

ing flag is positive, the time is assumed to be daylight saving time; if zero, the time is assumed to be standard time; and if negative (the default), mktime() attempts to determine whether

daylight saving time is in effect for the speci-

fied time. If datespec does not contain enough elements or if the resulting time is out of range,

mktime() returns -1.

strftime([format [, timestamp]]) Formats timestamp according to the specification in format. The timestamp should be of the same form as returned by systime(). If timestamp is

missing, the current time of day is used. If for-

mat is missing, a default format equivalent to the output of date(1) is used. See the specification

for the strftime() function in ANSI C for the for-

mat conversions that are guaranteed to be avail-

able. A public-domain version of strftime(3) and

a man page for it come with gawk; if that version

was used to build gawk, then all of the conver-

sions described in that man page are available to

gawk.

systime() Returns the current time of day as the number of

seconds since the Epoch (1970-01-01 00:00:00 UTC

on POSIX systems). Bit Manipulations Functions

Starting with version 3.1 of gawk, the following bit

Free Software FoundatLiaosnt change: June 26 2005 26 Utility Commands GAWK(1)

manipulation functions are available. They work by convert-

ing double-precision floating point values to unsigned long

integers, doing the operation, and then converting the result back to floating point. The functions are: and(v1, v2) Return the bitwise AND of the values provided by v1 and v2. compl(val) Return the bitwise complement of val. lshift(val, count) Return the value of val, shifted left by count bits.

or(v1, v2) Return the bitwise OR of the values pro-

vided by v1 and v2. rshift(val, count) Return the value of val, shifted right by count bits. xor(v1, v2) Return the bitwise XOR of the values provided by v1 and v2. Internationalization Functions

Starting with version 3.1 of gawk, the following functions

may be used from within your AWK program for translating

strings at run-time. For full details, see GAWK: Effective

AWK Programming. bindtextdomain(directory [, domain])

Specifies the directory where gawk looks for the .mo

files, in case they will not or cannot be placed in the ``standard'' locations (e.g., during testing). It returns the directory where domain is ``bound.'' The default domain is the value of TEXTDOMAIN. If directory is the null string (""), then bindtextdomain() returns the current binding for the given domain. dcgettext(string [, domain [, category]]) Returns the translation of string in text domain domain for locale category category. The default value for domain is the current value of TEXTDOMAIN. The default

value for category is "LC_MESSAGES".

If you supply a value for category, it must be a string equal to one of the known locale categories described

in GAWK: Effective AWK Programming. You must also sup-

ply a text domain. Use TEXTDOMAIN if you want to use the current domain. dcngettext(string1 , string2 , number [, domain [, category]])

Returns the plural form used for number of the transla-

tion of string1 and string2 in text domain domain for Free Software FoundatLiaosnt change: June 26 2005 27 Utility Commands GAWK(1) locale category category. The default value for domain is the current value of TEXTDOMAIN. The default value

for category is "LC_MESSAGES".

If you supply a value for category, it must be a string equal to one of the known locale categories described

in GAWK: Effective AWK Programming. You must also sup-

ply a text domain. Use TEXTDOMAIN if you want to use the current domain.

USER-DEFINED FUNCTIONS

Functions in AWK are defined as follows: function name(parameter list) { statements } Functions are executed when they are called from within

expressions in either patterns or actions. Actual parame-

ters supplied in the function call are used to instantiate the formal parameters declared in the function. Arrays are passed by reference, other variables are passed by value. Since functions were not originally part of the AWK language, the provision for local variables is rather

clumsy: They are declared as extra parameters in the parame-

ter list. The convention is to separate local variables from real parameters by extra spaces in the parameter list. For example:

function f(p, q, a, b) # a and b are local

{ ... } /abc/ { ... ; f(1, 2) ; ... } The left parenthesis in a function call is required to

immediately follow the function name, without any interven-

ing white space. This is to avoid a syntactic ambiguity with the concatenation operator. This restriction does not

apply to the built-in functions listed above.

Functions may call each other and may be recursive. Func-

tion parameters used as local variables are initialized to

the null string and the number zero upon function invoca-

tion. Use return expr to return a value from a function. The return value is undefined if no value is provided, or if the function returns by "falling off" the end.

If --lint has been provided, gawk warns about calls to unde-

fined functions at parse time, instead of at run time. Cal-

ling an undefined function at run time is a fatal error. Free Software FoundatLiaosnt change: June 26 2005 28 Utility Commands GAWK(1) The word func may be used in place of function. DYNAMICALLY LOADING NEW FUNCTIONS

Beginning with version 3.1 of gawk, you can dynamically add

new built-in functions to the running gawk interpreter. The

full details are beyond the scope of this manual page; see GAWK: Effective AWK Programming for the details. extension(object, function) Dynamically link the shared object file named by

object, and invoke function in that object, to per-

form initialization. These should both be provided as strings. Returns the value returned by function. This function is provided and documented in GAWK: Effective AWK Programming, but everything about this feature is likely to change in the next release. We STRONGLY recommend that you do not use this feature for anything that you aren't willing to redo. SIGNALS

pgawk accepts two signals. SIGUSR1 causes it to dump a pro-

file and function call stack to the profile file, which is

either awkprof.out, or whatever file was named with the

--profile option. It then continues to run. SIGHUP causes

it to dump the profile and function call stack and then exit.

EXAMPLES

Print and sort the login names of all users: BEGIN { FS = ":" }

{ print $1 | "sort" }

Count lines in a file: { nlines++ } END { print nlines } Precede each line by its number in the file:

{ print FNR, $0 }

Concatenate and line number (a variation on a theme):

{ print NR, $0 }

Run an external command for particular lines of data:

tail -f access_log |

awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'

Free Software FoundatLiaosnt change: June 26 2005 29 Utility Commands GAWK(1) INTERNATIONALIZATION String constants are sequences of characters enclosed in

double quotes. In non-English speaking environments, it is

possible to mark strings in the AWK program as requiring translation to the native natural language. Such strings are

marked in the AWK program with a leading underscore ("_").

For example,

gawk 'BEGIN { print "hello, world" }'

always prints hello, world. But,

gawk 'BEGIN { print _"hello, world" }'

might print bonjour, monde in France. There are several steps involved in producing and running a localizable AWK program. 1. Add a BEGIN action to assign a value to the TEXTDOMAIN variable to set the text domain to a name associated with your program. BEGIN { TEXTDOMAIN = "myprog" }

This allows gawk to find the .mo file associated with

your program. Without this step, gawk uses the messages

text domain, which likely does not contain translations for your program. 2. Mark all strings that should be translated with leading underscores. 3. If necessary, use the dcgettext() and/or

bindtextdomain() functions in your program, as appropri-

ate.

4. Run gawk --gen-po -f myprog.awk > myprog.po to generate

a .po file for your program. 5. Provide appropriate translations, and build and install a corresponding .mo file. The internationalization features are described in full detail in GAWK: Effective AWK Programming. POSIX COMPATIBILITY

A primary goal for gawk is compatibility with the POSIX

standard, as well as with the latest version of UNIX awk.

To this end, gawk incorporates the following user visible

features which are not described in the AWK book, but are

part of the Bell Laboratories version of awk, and are in the

Free Software FoundatLiaosnt change: June 26 2005 30 Utility Commands GAWK(1) POSIX standard. The book indicates that command line variable assignment

happens when awk would otherwise open the argument as a

file, which is after the BEGIN block is executed. However, in earlier implementations, when such an assignment appeared before any file names, the assignment would happen before the BEGIN block was run. Applications came to depend on

this "feature." When awk was changed to match its documen-

tation, the -v option for assigning variables before program

execution was added to accommodate applications that depended upon the old behavior. (This feature was agreed upon by both the Bell Laboratories and the GNU developers.)

The -W option for implementation specific features is from

the POSIX standard.

When processing arguments, gawk uses the special option "--"

to signal the end of arguments. In compatibility mode, it warns about but otherwise ignores undefined options. In normal operation, such arguments are passed on to the AWK program for it to process. The AWK book does not define the return value of srand(). The POSIX standard has it return the seed it was using, to allow keeping track of random number sequences. Therefore

srand() in gawk also returns its current seed.

Other new features are: The use of multiple -f options

(from MKS awk); the ENVIRON array; the \a, and \v escape

sequences (done originally in gawk and fed back into the

Bell Laboratories version); the tolower() and toupper()

built-in functions (from the Bell Laboratories version); and

the ANSI C conversion specifications in printf (done first in the Bell Laboratories version). HISTORICAL FEATURES There are two features of historical AWK implementations

that gawk supports. First, it is possible to call the

length() built-in function not only with no argument, but

even without parentheses! Thus,

a = length # Holy Algol 60, Batman!

is the same as either of a = length()

a = length($0)

This feature is marked as "deprecated" in the POSIX stan-

dard, and gawk issues a warning about its use if --lint is

specified on the command line. Free Software FoundatLiaosnt change: June 26 2005 31 Utility Commands GAWK(1) The other feature is the use of either the continue or the break statements outside the body of a while, for, or do loop. Traditional AWK implementations have treated such

usage as equivalent to the next statement. Gawk supports

this usage if --traditional has been specified.

GNU EXTENSIONS

Gawk has a number of extensions to POSIX awk. They are

described in this section. All the extensions described

here can be disabled by invoking gawk with the --traditional

option.

The following features of gawk are not available in POSIX

awk.

+o No path search is performed for files named via the -f

option. Therefore the AWKPATH environment variable is not special.

+o The \x escape sequence. (Disabled with --posix.)

+o The fflush() function. (Disabled with --posix.)

+o The ability to continue lines after ? and :. (Disabled

with --posix.)

+o Octal and hexadecimal constants in AWK programs.

+o The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN vari-

ables are not special.

+o The IGNORECASE variable and its side-effects are not

available.

+o The FIELDWIDTHS variable and fixed-width field splitting.

+o The PROCINFO array is not available. +o The use of RS as a regular expression.

+o The special file names available for I/O redirection are not recognized.

+o The |& operator for creating co-processes.

+o The ability to split out individual characters using the null string as the value of FS, and as the third argument to split(). +o The optional second argument to the close() function. +o The optional third argument to the match() function. Free Software FoundatLiaosnt change: June 26 2005 32 Utility Commands GAWK(1) +o The ability to use positional specifiers with printf and sprintf(). +o The use of delete array to delete the entire contents of an array. +o The use of nextfile to abandon processing of the current input file. +o The and(), asort(), asorti(), bindtextdomain(), compl(), dcgettext(), dcngettext(), gensub(), lshift(), mktime(), or(), rshift(), strftime(), strtonum(), systime() and xor() functions. +o Localizable strings.

+o Adding new built-in functions dynamically with the exten-

sion() function. The AWK book does not define the return value of the close()

function. Gawk's close() returns the value from fclose(3),

or pclose(3), when closing an output file or pipe, respec-

tively. It returns the process's exit status when closing

an input pipe. The return value is -1 if the named file,

pipe or co-process was not opened with a redirection.

When gawk is invoked with the --traditional option, if the

fs argument to the -F option is "t", then FS is set to the

tab character. Note that typing gawk -F\t ... simply causes

the shell to quote the "t,", and does not pass "\t" to the

-F option. Since this is a rather ugly special case, it is

not the default behavior. This behavior also does not occur

if --posix has been specified. To really get a tab charac-

ter as the field separator, it is best to use single quotes:

gawk -F'\t' ....

If gawk is configured with the --enable-switch option to the

configure command, then it accepts an additional control-

flow statement: switch (expression) { case value|regex : statement ... [ default: statement ] } ENVIRONMENT VARIABLES The AWKPATH environment variable can be used to provide a

list of directories that gawk searches when looking for

files named via the -f and --file options.

If POSIXLY_CORRECT exists in the environment, then gawk

behaves exactly as if --posix had been specified on the

Free Software FoundatLiaosnt change: June 26 2005 33 Utility Commands GAWK(1)

command line. If --lint has been specified, gawk issues a

warning message to this effect.

BUGS

The -F option is not necessary given the command line vari-

able assignment feature; it remains only for backwards com-

patibility. Syntactically invalid single character programs tend to

overflow the parse stack, generating a rather unhelpful mes-

sage. Such programs are surprisingly difficult to diagnose in the completely general case, and the effort to do so really is not worth it. AUTHORS

The original version of UNIX awk was designed and imple-

mented by Alfred Aho, Peter Weinberger, and Brian Kernighan of Bell Laboratories. Brian Kernighan continues to maintain and enhance it.

Paul Rubin and Jay Fenlason, of the Free Software Founda-

tion, wrote gawk, to be compatible with the original version

of awk distributed in Seventh Edition UNIX. John Woods con-

tributed a number of bug fixes. David Trueman, with contri-

butions from Arnold Robbins, made gawk compatible with the

new version of UNIX awk. Arnold Robbins is the current

maintainer.

The initial DOS port was done by Conrad Kwok and Scott Gar-

finkle. Scott Deifik is the current DOS maintainer. Pat Rankin did the port to VMS, and Michal Jaegermann did the port to the Atari ST. The port to OS/2 was done by Kai Uwe Rommel, with contributions and help from Darrel Hankerson. Fred Fish supplied support for the Amiga, Stephen Davies provided the Tandem port, and Martin Brown provided the BeOS port. VERSION INFORMATION

This man page documents gawk, version 3.1.5.

Free Software FoundatLiaosnt change: June 26 2005 34 Utility Commands GAWK(1) BUG REPORTS

If you find a bug in gawk, please send electronic mail to

bug-gawk@gnu.org. Please include your operating system and

its revision, the version of gawk (from gawk --version),

what C compiler you used to compile it, and a test program and data that are as small as possible for reproducing the problem. Before sending a bug report, please do two things. First,

verify that you have the latest version of gawk. Many bugs

(usually subtle ones) are fixed at each release, and if yours is out of date, the problem may already have been solved. Second, please read this man page and the reference manual carefully to be sure that what you think is a bug really is, instead of just a quirk in the language.

Whatever you do, do NOT post a bug report in comp.lang.awk.

While the gawk developers occasionally read this newsgroup,

posting bug reports there is an unreliable way to report bugs. Instead, please use the electronic mail addresses given above.

If you're using a GNU/Linux system or BSD-based system, you

may wish to submit a bug report to the vendor of your dis-

tribution. That's fine, but please send a copy to the offi-

cial email address as well, since there's no guarantee that

the bug will be forwarded to the gawk maintainer.

ACKNOWLEDGEMENTS Brian Kernighan of Bell Laboratories provided valuable assistance during testing and debugging. We thank him. COPYING PERMISSIONS Copyright cO 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997,

1998, 1999, 2001, 2002, 2003, 2004, 2005 Free Software Foun-

dation, Inc. Permission is granted to make and distribute verbatim copies of this manual page provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified ver-

sions of this manual page under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of

this manual page into another language, under the above con-

ditions for modified versions, except that this permission

notice may be stated in a translation approved by the Foun-

dation. Free Software FoundatLiaosnt change: June 26 2005 35 Utility Commands GAWK(1)

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

_______________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | text/gawk |

|____________________|__________________|_

| Interface Stability| Volatile |

|____________________|_________________|

NOTES

Source for gawk is available on http://opensolaris.org.

Free Software FoundatLiaosnt change: June 26 2005 36