Regex - Revision history

Sertonix: make note a warning

2023-09-20T18:19:19Z

make note a warning

← Older revision		Revision as of 18:19, 20 September 2023
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	This page summarizes some gritty regex details. It's not intended as a tutorial on any of these regex languages, but rather as a technical summary and list of "gotchas" (places where different implementations of a tool may behave in different or unexpected ways).		This page summarizes some gritty regex details. It's not intended as a tutorial on any of these regex languages, but rather as a technical summary and list of "gotchas" (places where different implementations of a tool 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 utilities reported here may have changed with the switch to musl.		{{Warning\|This summary was drawn up back when we were using uClibc. Some of the behavior of Alpine's utilities reported here may have changed with the switch to musl.}}

	__TOC__		__TOC__

Sertonix: use https

2023-08-25T21:39:23Z

use https

← Older revision		Revision as of 21:39, 25 August 2023
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	=== Regex engines ===		=== Regex engines ===

	The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [~~http~~://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [https://github.com/rrthomas/lrexlib Lrexlib] libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.		The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [https://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [https://github.com/rrthomas/lrexlib Lrexlib] libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.

	=== Regex specials ===		=== Regex specials ===

Zcrayfish: /* Regex engines */ fixed a dead link.

2023-08-25T15:09:43Z

Regex engines: fixed a dead link.

← Older revision		Revision as of 15:09, 25 August 2023
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	=== Regex engines ===		=== Regex engines ===

	The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [http://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [https://~~rrthomas.~~github.com/lrexlib/ Lrexlib]~~{{dead link}}~~ libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.		The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [http://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [https://github.com/rrthomas/lrexlib Lrexlib] libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.

	=== Regex specials ===		=== Regex specials ===

Sertonix: use https link

2023-08-25T02:44:07Z

use https link

← Older revision		Revision as of 02:44, 25 August 2023
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	=== Regex engines ===		=== Regex engines ===

	The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [http://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [~~http~~://rrthomas.github.com/lrexlib/ Lrexlib]{{dead link}} libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.		The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [http://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [https://rrthomas.github.com/lrexlib/ Lrexlib]{{dead link}} libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.

	=== Regex specials ===		=== Regex specials ===

Zcrayfish: Marked a dead link.

2021-12-20T02:15:23Z

Marked a dead link.

← Older revision		Revision as of 02:15, 20 December 2021
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	=== Regex engines ===		=== Regex engines ===

	The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [http://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [http://rrthomas.github.com/lrexlib/ Lrexlib] libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.		The basic Lua regex engine is more limited than the Posix- or PCRE-style languages, though still quite capable. In fact some things are more easily done with the Lua engine than with the more familiar ones. If the basic Lua engine is nonetheless too limited for your purposes, you should look into the [http://www.inf.puc-rio.br/~roberto/lpeg/ LPEG] or [http://rrthomas.github.com/lrexlib/ Lrexlib]{{dead link}} libraries. The former is more powerful and widely-used in the Lua community; the latter interfaces to more familiar regex engine libraries and languages.

	=== Regex specials ===		=== Regex specials ===

John3-16: Added internal link to Awk

2017-09-15T13:48:07Z

Added internal link to Awk

← Older revision		Revision as of 13:48, 15 September 2017
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	== POSIX regex ==		== POSIX regex ==

	POSIX defines two classes of regex languages: '''basic regular expressions (BREs)''' and '''extended regular expressions (EREs)'''. The first is historically implemented by utilities like <code>grep</code>, <code>sed</code>, and <code>ed</code>. The second by tools like <code>egrep</code> (<code>grep -E</code>), <code>awk</code>, <code>lex</code>, and <code>emacs</code>. EREs are usually also available as an option to <code>sed</code>; sometimes this is expressed using <code>sed -r</code>, other times <code>sed -E</code>. (BusyBox <code>sed</code> uses the first.)		POSIX defines two classes of regex languages: '''basic regular expressions (BREs)''' and '''extended regular expressions (EREs)'''. The first is historically implemented by utilities like <code>grep</code>, <code>sed</code>, and <code>ed</code>. The second by tools like <code>egrep</code> (<code>grep -E</code>), <code>[[awk]]</code>, <code>lex</code>, and <code>emacs</code>. EREs are usually also available as an option to <code>sed</code>; sometimes this is expressed using <code>sed -r</code>, other times <code>sed -E</code>. (BusyBox <code>sed</code> uses the first.)

	In practice most implementations of these regex languages go beyond the specification, for example including Gnu extensions like <code>\w</code>, or including features that were only historically available (and are only specified for) the other regex language: thus most implementations of BREs will also honor <code>\+</code> and <code>\\|</code>, and many implementations of EREs will also honor backreferences like <code>\1</code>. Additionally, <code>awk</code> EREs obeys somewhat different rules than other EREs.		In practice most implementations of these regex languages go beyond the specification, for example including Gnu extensions like <code>\w</code>, or including features that were only historically available (and are only specified for) the other regex language: thus most implementations of BREs will also honor <code>\+</code> and <code>\\|</code>, and many implementations of EREs will also honor backreferences like <code>\1</code>. Additionally, <code>awk</code> EREs obeys somewhat different rules than other EREs.

Dubiousjim: Add note about uClibc vs musl

2015-01-18T20:48:17Z

Add note about uClibc vs musl

← Older revision		Revision as of 20:48, 18 January 2015
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	This page summarizes some gritty regex details. It's not intended as a tutorial on any of these regex languages, but rather as a technical summary and list of "gotchas" (places where different implementations of a tool may behave in different or unexpected ways).		This page summarizes some gritty regex details. It's not intended as a tutorial on any of these regex languages, but rather as a technical summary and list of "gotchas" (places where different implementations of a tool 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 utilities reported here may have changed with the switch to musl.

	__TOC__		__TOC__

Dubiousjim: /* Regex specials */ tweak alternative for :print:

2013-02-01T13:21:25Z

Regex specials: tweak alternative for print:

← Older revision		Revision as of 13:21, 1 February 2013
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	'''%g''' and '''%G''' Like POSIX [[:graph:]] and [^[:graph:]], all visible characters except space; only so interpreted in Lua 5.2		'''%g''' and '''%G''' Like POSIX [[:graph:]] and [^[:graph:]], all visible characters except space; only so interpreted in Lua 5.2

	POSIX <code>[[:print:]]</code>, all visible characters plus space, isn't directly available. Use <code>[%p%a ]</code> or <code>[%g ]</code>.		POSIX <code>[[:print:]]</code>, all visible characters plus space, isn't directly available. Use <code>[%p%w ]</code> or <code>[%g ]</code>.

	<dt>Bracket expressions		<dt>Bracket expressions

Dubiousjim: /* Regex specials */ off-by-one error

2012-10-19T14:14:46Z

Regex specials: off-by-one error

← Older revision		Revision as of 14:14, 19 October 2012
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	<pre>		<pre>
	%f[%x] matches the source text "123-567 9ab" before positions 1, 5, and 9		%f[%x] matches the source text "123-567 9ab" before positions 1, 5, and 9
	%f[%X] matches the same source text before positions 4, 7, and 12.		%f[%X] matches the same source text before positions 4, 8, and 12.
	</pre>		</pre>
	</ul>		</ul>

Dubiousjim: /* Regex specials */ regex %p excludes cntrl

2012-06-01T12:18:44Z

Regex specials: regex %p excludes cntrl

← Older revision		Revision as of 12:18, 1 June 2012
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	'''%s''' and '''%S''' Like POSIX [[:space:]] and [^[:space:]].		'''%s''' and '''%S''' Like POSIX [[:space:]] and [^[:space:]].
	(%s and POSIX [[:space:]] do also match vertical space (\n \r \f \v, whereas POSIX [[:blank:]] matches only \x20 and tab.)		(%s and POSIX [[:space:]] do also match vertical space (\n \r \f \v, whereas POSIX [[:blank:]] matches only \x20 and tab.)
	'''%p''' and '''%P''' Like POSIX [[:punct:]] and [^[:punct:]], excludes space and alnum		'''%p''' and '''%P''' Like POSIX [[:punct:]] and [^[:punct:]], excludes space and alnum and cntrl
	'''%c''' and '''%C''' Like POSIX [[:cntrl:]] and [^[:cntrl:]]		'''%c''' and '''%C''' Like POSIX [[:cntrl:]] and [^[:cntrl:]]
	'''%g''' and '''%G''' Like POSIX [[:graph:]] and [^[:graph:]], all visible characters except space; only so interpreted in Lua 5.2		'''%g''' and '''%G''' Like POSIX [[:graph:]] and [^[:graph:]], all visible characters except space; only so interpreted in Lua 5.2