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AWK

Posted On 2007-04-25 by FortyPoundHead
Keywords: GAWK Command Reference
Tags: Linux Commandline Linux
Views: 1635


Find and Replace text, database sort/validate/index

Syntax


awk ''Program'' Input-File1 Input-File2 ...

awk -f PROGRAM-FILE Input-File1 Input-File2 ...

Key
`-F FS''
`--field-separator FS''
Use FS for the input field separator (the value of the `FS''
predefined variable).

`-f PROGRAM-FILE''
`--file PROGRAM-FILE''
Read the `awk'' program source from the file PROGRAM-FILE, instead
of from the first command line argument.

`-mf NNN''
`-mr NNN''
The `f'' flag sets the maximum number of fields, and the `r'' flag
sets the maximum record size. These options are ignored by
`gawk'', since `gawk'' has no predefined limits; they are only for
compatibility with the Bell Labs research version of Unix `awk''.

`-v VAR=VAL''
`--assign VAR=VAL''
Assign the variable VAR the value VAL before program execution
begins.

`-W traditional''
`-W compat''
`--traditional''
`--compat''
Use compatibility mode, in which `gawk'' extensions are turned off.

`-W lint''
`--lint''
Give warnings about dubious or non-portable `awk'' constructs.

`-W lint-old''
`--lint-old''
Warn about constructs that are not available in the original
Version 7 Unix version of `awk''.

`-W posix''
`--posix''
Use POSIX compatibility mode, in which `gawk'' extensions are
turned off and additional restrictions apply.

`-W re-interval''
`--re-interval''
Allow interval expressions, in regexps.

`-W source=PROGRAM-TEXT''
`--source PROGRAM-TEXT''
Use PROGRAM-TEXT as `awk'' program source code. This option allows
mixing command line source code with source code from files, and is
particularly useful for mixing command line programs with library
functions.

`--''
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 POSIX argument parsing conventions.

''Program''
A series of patterns and actions: see below

Input-File
If no Input-File is specified then `awk'' applies the Program to
"standard input", (piped output of some other command or the terminal.
Typed input will continue until end-of-file (typing `Control-d'')Basic functions

The basic function of awk is to search files for lines (or other units of text) that contain a pattern. When a line matches, awk performs a specific action on that line.

The Program statement that tells `awk'' what to do; consists of a series of "rules". Each rule specifies one pattern to search for, and one action to perform when that pattern is found.

For ease of reading, each line in an `awk'' program is normally a separate Program statement , like this:

pattern { action }
pattern { action }
...
e.g. Display lines from my_file containing the string "123" or "abc" or "some text":

awk ''/123/ { print $0 }
/abc/ { print $0 }
/some text/ { print $0 }'' my_fileA regular expression enclosed in slashes (`/'') is an `awk'' pattern that matches every input record whose text belongs to that set. e.g. the pattern /foo/ matches any input record containing the three characters `foo'', *anywhere* in the record.

`awk'' patterns may be one of the following:

/Regular Expression/ - Match =
Pattern && Pattern - AND
Pattern || Pattern - OR
! Pattern - NOT
Pattern ? Pattern : Pattern - If, Then, Else
Pattern1, Pattern2 - Range Start - end
BEGIN - Perform action BEFORE input file is read
END - Perform action AFTER input file is readIn addition to simple pattern matching `awk'' has a huge range of text and arithmetic Functions, Variables and Operators.

`gawk'' will ignore newlines after any of the following:

, { ? : || && do elseComments - start with a `#'', and continue to the end of the line:

# This program prints a nice friendly messageExamples

This program prints the length of the longest input line:

awk ''{ if (length($0) > max) max = length($0) }
END { print max }'' data
This program prints every line that has at least one field. This is an easy way to delete blank lines from a file (or rather, to
create a new file similar to the old file but from which the blank lines have been deleted)

awk ''NF > 0'' dataThis program prints seven random numbers from zero to 100, inclusive.

awk ''BEGIN { for (i = 1; i <= 7; i++)
print int(101 * rand()) }''
This program prints the total number of bytes used by FILES.

ls -lg FILES | awk ''{ x += $5 } ; END { print "total bytes: " x }''This program prints a sorted list of the login names of all users.

awk -F: ''{ print $1 }'' /etc/passwd | sortThis program counts lines in a file.

awk ''END { print NR }'' dataThis program prints the even numbered lines in the data file. If you were to use the expression `NR % 2 == 1'' instead, it would print the odd numbered lines.

awk ''NR % 2 == 0'' data


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