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NAME

gawk - pattern scanning and processing language  

SYNOPSIS

gawk [ <FONT SIZE="-1">POSIX</FONT> or <FONT SIZE="-1">GNU</FONT> style options ] -f program-file [ -- ] file ...
gawk [ <FONT SIZE="-1">POSIX</FONT> or <FONT SIZE="-1">GNU</FONT> style options ] [ -- ] program-text file ...

pgawk [ <FONT SIZE="-1">POSIX</FONT> or <FONT SIZE="-1">GNU</FONT> style options ] -f program-file [ -- ] file ...
pgawk [ <FONT SIZE="-1">POSIX</FONT> or <FONT SIZE="-1">GNU</FONT> style options ] [ -- ] program-text file ...  

DESCRIPTION

Gawk is the <FONT SIZE="-1">GNU</FONT> Project`s implementation of the <FONT SIZE="-1">AWK</FONT> programming language. It conforms to the definition of the language in the <FONT SIZE="-1">POSIX</FONT> 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 <FONT SIZE="-1">UNIX</FONT> awk. Gawk also provides more recent Bell Laboratories awk extensions, and a number of <FONT SIZE="-1">GNU</FONT>-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 <FONT SIZE="-1">AWK</FONT> program text (if not supplied via the -f or --file options), and values to be made available in the ARGC and ARGV pre-defined <FONT SIZE="-1">AWK</FONT> variables.  

OPTION FORMAT

Gawk options may be either traditional <FONT SIZE="-1">POSIX</FONT> one letter options, or <FONT SIZE="-1">GNU</FONT> style long options. <FONT SIZE="-1">POSIX</FONT> options start with a single ``-``, while long options start with ``--``. Long options are provided for both <FONT SIZE="-1">GNU</FONT>-specific features and for <FONT SIZE="-1">POSIX</FONT>-mandated features.

Following the <FONT SIZE="-1">POSIX</FONT> standard, gawk-specific options are supplied 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 intervening spaces, or they may be provided in the next command line argument. Long options may be abbreviated, as long as the abbreviation remains unique.  

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 execution of the program begins. Such variable values are available to the BEGIN block of an <FONT SIZE="-1">AWK</FONT> program.

-f program-file

--file program-file Read the <FONT SIZE="-1">AWK</FONT> program source from the file program-file, instead of from the first command line argument. Multiple -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 <FONT SIZE="-1">UNIX</FONT> 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 <FONT SIZE="-1">UNIX</FONT> awk; none of the <FONT SIZE="-1">GNU</FONT>-specific extensions are recognized. The use of --traditional is preferred over the other forms of this option. See GNU EXTENSIONS, below, for more information.

-W copyleft

-W copyright

--copyleft

--copyright Print the short version of the <FONT SIZE="-1">GNU</FONT> copyright information message on the standard output and exit successfully.

-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 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 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 <FONT SIZE="-1">AWK</FONT> implementations. With an optional argument of fatal, lint warnings become fatal errors. This may be drastic, but its use will certainly encourage the development of cleaner <FONT SIZE="-1">AWK</FONT> programs. 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.

-W gen-po

--gen-po Scan and parse the <FONT SIZE="-1">AWK</FONT> program, and generate a <FONT SIZE="-1">GNU</FONT> .po format file on standard output with entries for all localizable strings in the program. The program itself is not executed. See the <FONT SIZE="-1">GNU</FONT> gettext distribution for more information on .po files.

-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:

*

x escape sequences are not recognized.

*

Only space and tab act as field separators when FS is set to a single space, newline does not.

*

You cannot continue lines after ? and :.

*

The synonym func for the keyword function is not recognized.

*

The operators ** and **= cannot be used in place of ^ and ^=.

*

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 function 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 <FONT SIZE="-1">AWK</FONT> language. The <FONT SIZE="-1">POSIX</FONT> standard added them, to make awk and egrep consistent with each other. However, their use is likely to break old <FONT SIZE="-1">AWK</FONT> 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 <FONT SIZE="-1">AWK</FONT> 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 <FONT SIZE="-1">AWK</FONT> programs used in shell scripts.

-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 <FONT SIZE="-1">AWK</FONT> program itself to start with a ``-``. This is mainly for consistency with the argument parsing convention used by most other <FONT SIZE="-1">POSIX</FONT> 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 <FONT SIZE="-1">AWK</FONT> program in the ARGV array for processing. This is particularly useful for running <FONT SIZE="-1">AWK</FONT> programs via the ``#!`` executable interpreter mechanism.  

AWK PROGRAM EXECUTION

An <FONT SIZE="-1">AWK</FONT> 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 <FONT SIZE="-1">AWK</FONT> functions, without having to include them in each new <FONT SIZE="-1">AWK</FONT> 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 <FONT SIZE="-1">AWK</FONT> 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 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 variables <FONT SIZE="-1">AWK</FONT> 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 <FONT SIZE="-1">AWK</FONT> program. For each pattern that the record matches, the associated action is executed. The patterns are tested in the order they occur in the program.

Finally, after all the input is exhausted, gawk executes the code in the END block(s) (if any).  

VARIABLES, RECORDS AND FIELDS

<FONT SIZE="-1">AWK</FONT> 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. <FONT SIZE="-1">AWK</FONT> also has one dimensional arrays; arrays with multiple 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 regular 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. Otherwise, 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 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. References 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 processed.

ARGV

Array of command line arguments. The array is indexed from 0 to ARGC - 1. Dynamically changing 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 which gawk spawns via redirection or the system() function.

ERRNO

If a system error occurs either doing a redirection for getline, during a read for getline, or during a close(), then ERRNO will contain a string describing the error. The value is subject 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 gensub(), 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 <FONT SIZE="-1">AWK</FONT> 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.

LINT

Provides dynamic control of the --lint option from within an <FONT SIZE="-1">AWK</FONT> 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.

OFS

The output field separator, a space by default.

ORS

The output record separator, by default a newline.

PROCINFO

The elements of this array provide access to information about the running <FONT SIZE="-1">AWK</FONT> 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 splitting 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.

RS

The input record separator, by default a newline.

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 subscripts in array elements, by default "34".

TEXTDOMAIN

The text domain of the <FONT SIZE="-1">AWK</FONT> 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 (expr, expr ...) then the array subscript is a string consisting 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 "

assigns the string "hello, world " to the element of the array x which is indexed by the string "A34B34C". All arrays in <FONT SIZE="-1">AWK</FONT> are associative, i.e. indexed by string values.

The special operator in may be used in an if or while statement to see if an array has an index consisting of a particular 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 interpreted 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 <FONT SIZE="-1">AWK</FONT> 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. Otherwise, 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 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 <FONT SIZE="-1">AWK</FONT> 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 <FONT SIZE="-1">ASCII</FONT> <FONT SIZE="-1">BEL</FONT> character.



backspace.

f

form-feed.

newline.

carriage return.

horizontal tab.

v

vertical tab.

xhex digits

The character represented by the string of hexadecimal digits following the x. As in <FONT SIZE="-1">ANSI</FONT> 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 <FONT SIZE="-1">ASCII</FONT> <FONT SIZE="-1">ESC</FONT> (escape) character.

ddd

The character represented by the 1-, 2-, or 3-digit sequence of octal digits. E.g., "33" is the <FONT SIZE="-1">ASCII</FONT> <FONT SIZE="-1">ESC</FONT> (escape) character.

c

The literal character c.

The escape sequences may also be used inside constant regular expressions (e.g., /[  f 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, /a52b/ is equivalent to /a*b/.  

PATTERNS AND ACTIONS

<FONT SIZE="-1">AWK</FONT> 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 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, however, 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

<FONT SIZE="-1">AWK</FONT> 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 written 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 expressions. 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 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 interval 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 command 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.

`

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 <FONT SIZE="-1">POSIX</FONT> standard. A character class is a special notation for describing lists of characters that have a specific attribute, but where the actual characters themselves can vary from country to country and/or from character set to character 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 <FONT SIZE="-1">POSIX</FONT> 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.

For example, before the <FONT SIZE="-1">POSIX</FONT> 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 <FONT SIZE="-1">ASCII</FONT>, this might not even match the <FONT SIZE="-1">ASCII</FONT> alphanumeric characters. With the <FONT SIZE="-1">POSIX</FONT> 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-<FONT SIZE="-1">ASCII</FONT> 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 element enclosed in [. and .]. For example, if ch is a collating element, then [[.ch.]] is a regular expression 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 <FONT SIZE="-1">POSIX</FONT> 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 <FONT SIZE="-1">GNU</FONT> 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 <FONT SIZE="-1">POSIX</FONT> regular expressions and the <FONT SIZE="-1">GNU</FONT> regular expression operators described above. However, interval expressions are not supported.

--posix

Only <FONT SIZE="-1">POSIX</FONT> regular expressions are supported, the <FONT SIZE="-1">GNU</FONT> operators are not special. (E.g., w matches a literal w). Interval expressions are allowed.

--traditional

Traditional Unix awk regular expressions are matched. The <FONT SIZE="-1">GNU</FONT> operators are not special, interval expressions are not available, and neither are the <FONT SIZE="-1">POSIX</FONT> 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 <FONT SIZE="-1">AWK</FONT>, in order of decreasing precedence, are

(...)

Grouping

$

Field reference.

++ --

Increment and decrement, both prefix and postfix.

^

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/) 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 <file

Set $0 from next record of file; set NF.

getline var

Set var from next input record; set NR, FNR.

getline var <file

Set var from next record of file.

command | getline [var]

Run command piping the output either 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 extension.

next

Stop processing the current input record. The next input record is read and processing starts over with the first pattern in the <FONT SIZE="-1">AWK</FONT> program. If the end of the input data is reached, the END block(s), if any, are executed.

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 <FONT SIZE="-1">AWK</FONT> 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 terminated 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

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-<FONT SIZE="-1">POSIX</FONT> 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. <FONT SIZE="-1">AWK</FONT> does not automatically close pipes or co-processes when they return EOF.  

The printf Statement

The <FONT SIZE="-1">AWK</FONT> versions of the printf statement and sprintf() function (see below) accept the following conversion specification formats:

%c

An <FONT SIZE="-1">ASCII</FONT> 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.

%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 formatting. 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 program. 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 positive. 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. For %g, and %G, trailing zeros are not removed from the result.

0

A leading 0 (zero) acts as a flag, that indicates output 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 specifies 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 specifies 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 <FONT SIZE="-1">ANSI</FONT> 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, supply the count$ after the * in the format string. For example, "%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 process (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 descriptor n.

These are particularly useful for error messages. For example:

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 provide. 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 terminated 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

<FONT SIZE="-1">AWK</FONT> has the following built-in arithmetic functions:

atan2(y, x)

Returns the arctangent of y/x in radians.

cos(expr)

Returns the cosine of expr, which is in radians.

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 previous 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 duplicated 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 numerically, 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 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 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 target string is not changed.

gsub(r, s [, t])

For each substring matching the regular 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 replacement text of sub(), gsub(), and gensub().)

index(s, t)

Returns the index of the string t in the string s, or 0 if t is not present. (This implies that character indices start at one.)

length([s])

Returns the length of the string s, or the length of $0 if s is not supplied.

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. 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 splitting, 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 substring 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 counterparts. 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 counterparts. Non-alphabetic characters are left unchanged.

 

Time Functions

Since one of the primary uses of <FONT SIZE="-1">AWK</FONT> programs is processing log files that contain time stamp information, gawk provides the following functions for obtaining time stamps and formatting 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 saving 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 specified 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 format is missing, a default format equivalent to the output of date(1) is used. See the specification for the strftime() function in <FONT SIZE="-1">ANSI</FONT> C for the format conversions that are guaranteed to be available. 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 conversions 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 <FONT SIZE="-1">POSIX</FONT> systems).

 

Bit Manipulations Functions

Starting with version 3.1 of gawk, the following bit manipulation functions are available. They work by converting 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 provided 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<