Awk - Revision history

Dubiousjim: add some line breaks

2024-11-09T07:42:29Z

add some line breaks

← Older revision		Revision as of 07:42, 9 November 2024
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	The expression `k in array` doesn't create an array entry, but the reference `array[k]` will create an entry with an uninitialized value. (`k in array` will then be true.)		The expression `k in array` doesn't create an array entry, but the reference `array[k]` will create an entry with an uninitialized value. (`k in array`
			will then be true.)

	References to fields > NF, on the other hand, don't create new fields. Assignments to these fields do create them (increasing NF and setting any intermediate fields to uninitialized values). Assignments to any field (even <= NF) cause $0 to be recomputed using OFS, but do not cause $0 to be reparsed. (So the modified/new field may contain embedded FS characters.)		References to fields > NF, on the other hand, don't create new fields. Assignments to these fields do create them (increasing NF and setting any
			intermediate fields to uninitialized values). Assignments to any field (even <= NF) cause $0 to be recomputed using OFS, but do not cause $0 to be
			reparsed. (So the modified/new field may contain embedded FS characters.)

	Assignments to $0 do cause NF, $1, ... to be recomputed.		Assignments to $0 do cause NF, $1, ... to be recomputed.
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	<div style="white-space:pre; font-family:monospace;"><nowiki>		<div style="white-space:pre; font-family:monospace;"><nowiki>

	Uninitialized values include unset variables and array elements, invalid fields (> NF) or valid fields of length 0, and unassigned function parms (which can be used as scalars or arrays). Unititalized scalars have value "", which math operators treat as 0.		Uninitialized values include unset variables and array elements, invalid fields (> NF) or valid fields of length 0, and unassigned function parms
			(which can be used as scalars or arrays). Unititalized scalars have value "", which math operators treat as 0.
	Can force string interpretaton by `var ""`, or force numeric interpretation by `var + 0`. "1text" is coerced as 1.		Can force string interpretaton by `var ""`, or force numeric interpretation by `var + 0`. "1text" is coerced as 1.
	In boolean contexts: false when expr evaluates to 0 or "", else true.		In boolean contexts: false when expr evaluates to 0 or "", else true.
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	close("file" or "pipe commnd") ~~> 0 if successful		close("file" or "pipe commnd") ~~> 0 if successful
	# awk doesn't automatically close files, pipes, sockets, or co-processes when they return EOF.		# awk doesn't automatically close files, pipes, sockets, or co-processes when they return EOF.
	# the return value of close() is unspecified; gawk uses value from fclose(3) or pclose(3), or -1 if the named file, piple, or co-process was not opened with a redirection.		# the return value of close() is unspecified; gawk uses value from fclose(3) or pclose(3), or -1 if the named file, piple, or co-process was not
			opened with a redirection.
	{ print ... \| "sort>tmpfile" } END { close("sort>tmpfile"); while ((getline < "tmpfile")>0) ... close("tmpfile") }		{ print ... \| "sort>tmpfile" } END { close("sort>tmpfile"); while ((getline < "tmpfile")>0) ... close("tmpfile") }

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	POSIX requires that assigning a new value to FS has no effect on the current input line; it only affects the next input line.		POSIX requires that assigning a new value to FS has no effect on the current input line; it only affects the next input line.
	Only gawk conforms; BusyBox and FreeBSD awk will also use the new FS for current line if no fields have yet been referenced.		Only gawk conforms; BusyBox and FreeBSD awk will also use the new FS for current line if no fields have yet been referenced.
	FS=space (default): strips leading and trailing space/tabs, fields are separated by spans of space/tabs/newlines (in gawk --posix, only spans of spaces/tabs)		FS=space (default): strips leading and trailing space/tabs, fields are separated by spans of space/tabs/newlines (in gawk --posix, only spans of
			spaces/tabs)
	FS=":" or "\t": each occurrence of the char separates another field		FS=":" or "\t": each occurrence of the char separates another field
	FS="pat": separator is leftmost longest non-null and non-overlapping match of pattern		FS="pat": separator is leftmost longest non-null and non-overlapping match of pattern

Sertonix: use https link

2023-08-25T02:44:49Z

use https link

← Older revision		Revision as of 02:44, 25 August 2023
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	* https://www.pement.org/awk/awk1line.txt		* https://www.pement.org/awk/awk1line.txt
	* ~~http~~://www.catonmat.net/series/awk-one-liners-explained		* https://www.catonmat.net/series/awk-one-liners-explained
	* http://awk.freeshell.org/HomePage		* http://awk.freeshell.org/HomePage
	* http://awk.freeshell.org/AwkFeatureComparison		* http://awk.freeshell.org/AwkFeatureComparison

Zcrayfish: Changed some hyperlinks to https

2023-07-26T12:43:02Z

Changed some hyperlinks to https

← Older revision		Revision as of 12:43, 26 July 2023
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	{{DISPLAYTITLE:awk}}		{{DISPLAYTITLE:awk}}

	This page compares BusyBox's implementation of awk (using [~~http~~://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [https://ia903404.us.archive.org/0/items/pdfy-MgN0H1joIoDVoIC7/The_AWK_Programming_Language.pdf Bell Labs/Brian Kernighan's 2007 version of awk].		This page compares BusyBox's implementation of awk (using [https://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [https://ia903404.us.archive.org/0/items/pdfy-MgN0H1joIoDVoIC7/The_AWK_Programming_Language.pdf Bell Labs/Brian Kernighan's 2007 version of awk].

	It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).		It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).
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	@include "filename"		@include "filename"

	This is only available in some versions of gawk. See also Aleksey Cheusov's [~~http~~://runawk.sourceforge.net/ Runawk], which uses a different approach.		This is only available in some versions of gawk. See also Aleksey Cheusov's [https://runawk.sourceforge.net/ Runawk], which uses a different approach.

	=== Statements ===		=== Statements ===
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	These links may also be of interest:		These links may also be of interest:

	* ~~http~~://www.pement.org/awk/awk1line.txt		* https://www.pement.org/awk/awk1line.txt
	* http://www.catonmat.net/series/awk-one-liners-explained		* http://www.catonmat.net/series/awk-one-liners-explained
	* http://awk.freeshell.org/HomePage		* http://awk.freeshell.org/HomePage

Psykose: lowercase title

2022-10-18T05:55:26Z

lowercase title

← Older revision		Revision as of 05:55, 18 October 2022
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			{{DISPLAYTITLE:awk}}

	This page compares BusyBox's implementation of awk (using [http://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [https://ia903404.us.archive.org/0/items/pdfy-MgN0H1joIoDVoIC7/The_AWK_Programming_Language.pdf Bell Labs/Brian Kernighan's 2007 version of awk].		This page compares BusyBox's implementation of awk (using [http://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [https://ia903404.us.archive.org/0/items/pdfy-MgN0H1joIoDVoIC7/The_AWK_Programming_Language.pdf Bell Labs/Brian Kernighan's 2007 version of awk].

Zcrayfish: Used note template

2021-12-23T03:20:21Z

Used note template

← Older revision		Revision as of 03:20, 23 December 2021
Line 3:		Line 3:
	It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).		It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).

	~~'''Note:'''~~ This summary was drawn up back when we were using uClibc. Some of the behavior of Alpine's version of BusyBox awk reported here may have changed with the switch to musl.		{{note\|This summary was drawn up back when we were using uClibc. Some of the behavior of Alpine's version of BusyBox awk reported here may have changed with the switch to musl.}}

	__TOC__		__TOC__

Zcrayfish: Rescued a dead link.

2021-12-23T03:19:47Z

Rescued a dead link.

← Older revision		Revision as of 03:19, 23 December 2021
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	This page compares BusyBox's implementation of awk (using [http://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [~~http~~://~~www~~.cs.~~bell-labs~~.~~com~~/cm/cs/~~awkbook~~/~~index~~.~~html~~ Bell Labs/Brian Kernighan's 2007 version of awk]~~{{dead link}}. <!-- his newer site is at http://www.cs.princeton.edu/~bwk/btl~~.~~mirror/ -->~~		This page compares BusyBox's implementation of awk (using [http://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [https://ia903404.us.archive.org/0/items/pdfy-MgN0H1joIoDVoIC7/The_AWK_Programming_Language.pdf Bell Labs/Brian Kernighan's 2007 version of awk].

	It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).		It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).

Zcrayfish: Marked a dead link.

2021-12-20T01:57:59Z

Marked a dead link.

← Older revision		Revision as of 01:57, 20 December 2021
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	This page compares BusyBox's implementation of awk (using [http://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [http://www.cs.bell-labs.com/cm/cs/awkbook/index.html Bell Labs/Brian Kernighan's 2007 version of awk]. <!-- his newer site is at http://www.cs.princeton.edu/~bwk/btl.mirror/ -->		This page compares BusyBox's implementation of awk (using [http://git.alpinelinux.org/cgit/aports/tree/main/busybox/busyboxconfig?id=v2.3.6 this] config file) with gawk (versions >= 3.1.8) and FreeBSD 9's nawk, which is based on [http://www.cs.bell-labs.com/cm/cs/awkbook/index.html Bell Labs/Brian Kernighan's 2007 version of awk]{{dead link}}. <!-- his newer site is at http://www.cs.princeton.edu/~bwk/btl.mirror/ -->

	It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).		It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).

Dubiousjim: Add note about uClibc vs musl

2015-01-18T20:47:36Z

Add note about uClibc vs musl

← Older revision		Revision as of 20:47, 18 January 2015
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	It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).		It's not intended as a tutorial, but rather as a technical summary and list of "gotchas" (places where different implementations may behave in different or unexpected ways).

			'''Note:''' This summary was drawn up back when we were using uClibc. Some of the behavior of Alpine's version of BusyBox awk reported here may have changed with the switch to musl.

	__TOC__		__TOC__

Dubiousjim: /* Statements */ formatting

2013-01-09T20:27:55Z

Statements: formatting

← Older revision		Revision as of 20:27, 9 January 2013
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	NR==1 {...<var>handle first line</var>...; next }		NR==1 {...<var>handle first line</var>...; next }
	{...<var>handle other lines</var>...}		{...<var>handle other lines</var>...}

	POSIX doesn't specify the behavior of <code>next</code> in BEGIN or END blocks.		POSIX doesn't specify the behavior of <code>next</code> in BEGIN or END blocks.

Dubiousjim: /* Statements */ s/=/==/

2013-01-09T20:25:58Z

Statements: s/=/==/

← Older revision		Revision as of 20:25, 9 January 2013
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	This reads the next line of input and restarts the main loop from the first rule. For example, to treat the first line of awk's input specially, you can do this:		This reads the next line of input and restarts the main loop from the first rule. For example, to treat the first line of awk's input specially, you can do this:

	NR=1 {...<var>handle first line</var>...; next }		NR==1 {...<var>handle first line</var>...; next }
	{...<var>handle other lines</var>...}		{...<var>handle other lines</var>...}