home | O'Reilly's CD bookshelfs | FreeBSD | Linux | Cisco | Cisco Exam  

Book HomeBook TitleSearch this book

11.10. Alphabetical Summary of Functions and Commands

The following alphabetical list of keywords and functions includes all that are available in awk, nawk, and gawk. nawk includes all old awk functions and keywords, plus some additional ones (marked as {N}). gawk includes all nawk functions and keywords, plus some additional ones (marked as {G}). Items marked with {B} are available in the Bell Labs awk. Items that aren't marked with a symbol are available in all versions.


atan2(y, x)

Return the arctangent of y/x in radians. {N}



Exit from a while, for, or do loop.



In most implementations of awk, you can have only 10 files open simultaneously and one pipe. Therefore, nawk provides a close function that allows you to close a file or a pipe. It takes as an argument the same expression that opened the pipe or file. This expression must be identical, character by character, to the one that opened the file or pipe; even whitespace is significant. {N}



Begin next iteration of while, for, or do loop.



Return the cosine of x, an angle in radians. {N}


delete array[element]
tt class="literal">delete

Delete element from array. The brackets are typed literally. The second form is a common extension, which deletes all elements of the array at one shot. {N}


while (expr

Looping statement. Execute statement, then evaluate expr and, if true, execute statement again. A series of statements must be put within braces. {N}


exit [expr]

Exit from script, reading no new input. The END procedure, if it exists, will be executed. An optional expr becomes awk's return value.



Return exponential of x (ex).



Flush any buffers associated with open output file or pipe output-expr. {B}

gawk extends this function. If no output-expr is supplied, it flushes standard output. If output-expr is the null string (""), it flushes all open files and pipes. {G}


for (init-expr; test-expr; incr-expr)

C-style looping construct. init-expr assigns the initial value of a counter variable. test-expr is a relational expression that is evaluated each time before executing the statement. When test-expr is false, the loop is exited. incr-expr increments the counter variable after each pass. All the expressions are optional. A missing test-expr is considered to be true. A series of statements must be put within braces.


for (item in array)

Special loop designed for reading associative arrays. For each element of the array, the statement is executed; the element can be referenced by array[item]. A series of statements must be put within braces.


function name(parameter-list) {


Create name as a user-defined function consisting of awk statements that apply to the specified list of parameters. No space is allowed between name and the left paren when the function is called. {N}


getline [var] [< file]
command | getline [var

Read next line of input. Original awk doesn't support the syntax to open multiple input streams. The first form reads input from file; the second form reads the output of command. Both forms read one record at a time, and each time the statement is executed, it gets the next record of input. The record is assigned to $0 and is parsed into fields, setting NF, NR and FNR. If var is specified, the result is assigned to var, and $0 and NF aren't changed. Thus, if the result is assigned to a variable, the current record doesn't change. getline is actually a function and returns 1 if it reads a record successfully, 0 if end-of-file is encountered, and -1 if it's otherwise unsuccessful. {N}


gensub(r, s, h [, t])

General substitution function. Substitute s for matches of the regular expression r in the string t. If h is a number, replace the hth match. If it is "g" or "G", substitute globally. If t is not supplied, $0 is used. Return the new string value. The original t is not modified. (Compare gsub and sub.) {G}


gsub(r, s [, t])

Globally substitute s for each match of the regular expression r in the string t. If t is not supplied, defaults to $0. Return the number of substitutions. {N}


if (condition)

If condition is true, do statement(s); otherwise do statement in the optional else clause. The condition can be an expression using any of the relational operators <, <=, ==, !=, >=, or >, as well as the array membership operator in, and the pattern-matching operators ~ and !~ (e.g., if ($1 ~ /[Aa].*/)). A series of statements must be put within braces. Another if can directly follow an else in order to produce a chain of tests or decisions.


index(str, substr)

Return the position (starting at 1) of substr in str, or zero if substr is not present in str.



Return integer value of x by truncating any fractional part.



Return length of arg, or the length of $0 if no argument.



Return the natural logarithm (base e) of x.


match(s, r)

Function that matches the pattern, specified by the regular expression r, in the string s, and returns either the position in s, where the match begins, or 0 if no occurrences are found. Sets the values of RSTART and RLENGTH to the start and length of the match, respectively. {N}



Read next input line and start new cycle through pattern/procedures statements.



Stop processing the current input file and start new cycle through pattern/procedures statements, beginning with the first record of the next file. {B} {G}


print [ output-expr[, ...]] [ dest-expr ]

Evaluate the output-expr and direct it to standard output, followed by the value of ORS. Each comma-separated output-expr is separated in the output by the value of OFS. With no output-expr, print $0.

Output Redirections

dest-expr is an optional expression that directs the output to a file or pipe.

> file
Directs the output to a file, overwriting its previous contents.

>> file
Appends the output to a file, preserving its previous contents. In both cases, the file is created if it does not already exist.

| command
Directs the output as the input to a Unix command.

Be careful not to mix > and >> for the same file. Once a file has been opened with >, subsequent output statements continue to append to the file until it is closed.

Remember to call close() when you have finished with a file or pipe. If you don't, eventually you will hit the system limit on the number of simultaneously open files.


printf(format [, expr-list ]) [ dest-expr ]

An alternative output statement borrowed from the C language. It can produce formatted output and also output data without automatically producing a newline. format is a string of format specifications and constants. expr-list is a list of arguments corresponding to format specifiers. See print for a description of dest-expr.

format follows the conventions of the C-language printf(3S) library function. Here are a few of the most common formats:


A string.


A decimal number.


A floating-point number; n = total number of digits. m = number of digits after decimal point.


n specifies minimum field length for format type c, while - left-justifies value in field; otherwise, value is right-justified.

Like any string, format can also contain embedded escape sequences: \n (newline) or \t (tab) being the most common. Spaces and literal text can be placed in the format argument by quoting the entire argument. If there are multiple expressions to be printed, there should be multiple formats specified.


Using the script:

{ printf("The sum on line %d is %.0f.\n", NR, $1+$2) }

The following input line:

5   5

produces this output, followed by a newline:

The sum on line 1 is 10.


Generate a random number between 0 and 1. This function returns the same series of numbers each time the script is executed, unless the random number generator is seeded using srand(). {N}


return [expr]

Used within a user-defined function to exit the function, returning value of expr. The return value of a function is undefined if expr is not provided. {N}



Return the sine of x, an angle in radians. {N}


split(string, array [, sep])

Split string into elements of array array[1],...,array[n]. The string is split at each occurrence of separator sep. If sep is not specified, FS is used. The number of array elements created is returned.


sprintf(format [, expressions])

Return the formatted value of one or more expressions, using the specified format (see printf). Data is formatted but not printed. {N}



Return square root of arg.



Use optional expr to set a new seed for the random number generator. Default is the time of day. Return value is the old seed. {N}


strftime([format [,timestamp]])

Format timestamp according to format. Return the formatted string. The timestamp is a time-of-day value in seconds since midnight, January 1, 1970, UTC. The format string is similar to that of sprintf. (See the Example for systime.) If timestamp is omitted, it defaults to the current time. If format is omitted, it defaults to a value that produces output similar to that of date. {G}


sub(r, s [, t])

Substitute s for first match of the regular expression r in the string t. If t is not supplied, defaults to $0. Return 1 if successful; 0 otherwise. {N}


substr(string, beg [, len])

Return substring of string at beginning position beg and the characters that follow to maximum specified length len. If no length is given, use the rest of the string.



Function that executes the specified command and returns its status. The status of the executed command typically indicates success or failure. A value of 0 means that the command executed successfully. A nonzero value indicates a failure of some sort. The documentation for the command you're running will give you the details.

The output of the command is not available for processing within the awk script. Use command | getline to read the output of a command into the script. {N}



Return a time-of-day value in seconds since midnight, January 1, 1970, UTC. {G}


Log the start and end times of a data-processing program:

	now = systime()
	mesg = strftime("Started at %m/%d/%Y %H:%M:%S", now)
	print mesg
process data ...
	now = systime()
	mesg = strftime("Ended at %m/%d/%Y %H:%M:%S", now)
	print mesg


Translate all uppercase characters in str to lowercase and return the new string.[15] {N}

[15]Very early versions of nawk don't support tolower() and toupper(). However, they are now part of the POSIX specification for awk, and are included in the SVR4 nawk.



Translate all lowercase characters in str to uppercase and return the new string. {N}


while (condition)

Do statement while condition is true (see if for a description of allowable conditions). A series of statements must be put within braces.

11.10.1. printf Formats

Format specifiers for printf and sprintf have the following form:


The control letter is required. The format conversion control letters are as follows.

cASCII character
dDecimal integer
iDecimal integer (added in POSIX)
eFloating-point format ([-]d.precisione[+-]dd)
EFloating-point format ([-]d.precisionE[+-]dd)
fFloating-point format ([-]ddd.precision)
ge or f conversion, whichever is shortest, with trailing zeros removed
GE or f conversion, whichever is shortest, with trailing zeros removed
oUnsigned octal value
xUnsigned hexadecimal number; uses a-f for 10 to 15
XUnsigned hexadecimal number; uses A-F for 10 to 15
%Literal %

The optional flag is one of the following.


Left-justify the formatted value within the field.


Prefix positive values with a space and negative values with a minus.


Always prefix numeric values with a sign, even if the value is positive.


Use an alternate form: %o has a preceding 0; %x and %X are prefixed with 0x and 0X, respectively; %e, %E, and %f always have a decimal point in the result; and %g and %G do not have trailing zeros removed.


Pad output with zeros, not spaces. This happens only when the field width is wider than the converted result.

The optional width is the minimum number of characters to output. The result will be padded to this size if it is smaller. The 0 flag causes padding with zeros; otherwise, padding is with spaces.

The precision is optional. Its meaning varies by control letter, as shown in this table.

ConversionPrecision Means

%d, %i, %o

%u, %x, %X

The minimum number of digits to print
%e, %E, %f The number of digits to the right of the decimal point
%g, %GThe maximum number of significant digits
%sThe maximum number of characters to print

Library Navigation Links

Copyright © 2003 O'Reilly & Associates. All rights reserved.