{"id":638,"date":"2014-11-07T11:45:17","date_gmt":"2014-11-07T04:45:17","guid":{"rendered":"http:\/\/blog.trichev.com\/?p=638"},"modified":"2017-08-10T09:24:37","modified_gmt":"2017-08-10T02:24:37","slug":"perl-regular-expressions","status":"publish","type":"post","link":"https:\/\/trichev.com\/blog\/2014\/11\/07\/perl-regular-expressions\/","title":{"rendered":"Perl. Regular expressions"},"content":{"rendered":"\n\n\n
\n

Metacharacters<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
char<\/th>\nmeaning<\/th>\n<\/tr>\n
^<\/code><\/big><\/th>\nbeginning of string<\/td>\n<\/tr>\n
$<\/code><\/big><\/th>\nend of string<\/td>\n<\/tr>\n
.<\/code><\/big><\/th>\nany character except newline<\/td>\n<\/tr>\n
*<\/code><\/big><\/th>\nmatch 0 or more times<\/td>\n<\/tr>\n
+<\/code><\/big><\/th>\nmatch 1 or more times<\/td>\n<\/tr>\n
?<\/code><\/big><\/th>\nmatch 0 or 1 times; or<\/em>: shortest match<\/td>\n<\/tr>\n
|<\/code><\/big><\/th>\nalternative<\/td>\n<\/tr>\n
( )<\/code><\/big><\/th>\ngrouping; \u201cstoring\u201d<\/td>\n<\/tr>\n
[ ]<\/code><\/big><\/th>\nset of characters<\/td>\n<\/tr>\n
{ }<\/code><\/big><\/th>\nrepetition modifier<\/td>\n<\/tr>\n
\\<\/code><\/big><\/th>\nquote or special<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

To present a metacharacter as a data character standing for itself, precede it with \\<\/code> (e.g. \\.<\/code> matches the full stop character .<\/code> only).<\/small><\/p>\n

In the table above, the characters themselves, in the first column, are links to descriptions of characters in my The ISO Latin 1 character repertoire\u00a0– a description with usage notes<\/a><\/cite>. Note that the physical appearance (glyph<\/a>) of a character may vary from one device or program or font to another.<\/small><\/td>\n

\n

Repetition<\/h2>\n\n\n\n\n\n\n\n\n\n
a<\/var>*<\/code><\/td>\nzero or more a<\/var>\u2019s<\/td>\n<\/tr>\n
a<\/var>+<\/code><\/td>\none or more a<\/var>\u2019s<\/td>\n<\/tr>\n
a<\/var>?<\/code><\/td>\nzero or one a<\/var>\u2019s (i.e., optional a<\/var>)<\/td>\n<\/tr>\n
a<\/var>{<\/code>m<\/var>}<\/code><\/td>\nexactly m<\/var> a<\/var>\u2019s<\/td>\n<\/tr>\n
a<\/var>{<\/code>m<\/var>,}<\/code><\/td>\nat least m<\/var> a<\/var>\u2019s<\/td>\n<\/tr>\n
a<\/var>{<\/code>m<\/var>,<\/code>n<\/var>}<\/code><\/td>\nat least m<\/var> but at most n <\/var>a<\/var>\u2019s<\/td>\n<\/tr>\n
repetition<\/var>?<\/code><\/td>\nsame as repetition<\/var> but the shortest<\/em> match is taken<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Read the notation a<\/var>\u2019s as \u201coccurrences of strings, each of which matches the pattern a<\/var>\u201d. Read repetition<\/var> as any of the repetition expressions listed above it. Shortest match means that the shortest string matching the pattern is taken. The default is \u201cgreedy matching\u201d<\/a>, which finds the longest match. The repetition<\/var>?<\/code> construct was introduced in Perl version\u00a05.<\/small><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

<\/a>Special notations with \\<\/code><\/h2>\n\n\n\n
\n\n\n\n\n\n\n
Single characters<\/caption>\n
\\t<\/code><\/td>\ntab<\/td>\n<\/tr>\n
\\n<\/code><\/td>\nnewline<\/td>\n<\/tr>\n
\\r<\/code><\/td>\nreturn (CR)<\/td>\n<\/tr>\n
\\x<\/code>hh<\/var><\/td>\ncharacter with hex. code hh<\/var><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/td>\n\n\n\n\n\n
\u201cZero-width assertions\u201d<\/caption>\n
\\b<\/code><\/td>\n\u201cword\u201d boundary<\/td>\n<\/tr>\n
\\B<\/code><\/td>\nnot a \u201cword\u201d boundary<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n\n\n\n\n\n
Matching<\/caption>\n
\\w<\/code><\/td>\nmatches any single<\/em> character classified as a \u201cword\u201d character (alphanumeric or \u201c_<\/code>\u201d)<\/td>\n<\/tr>\n
\\W<\/code><\/td>\nmatches any non-\u201cword\u201d character<\/td>\n<\/tr>\n
\\s<\/code><\/td>\nmatches any whitespace character (space, tab, newline)<\/td>\n<\/tr>\n
\\S<\/code><\/td>\nmatches any non-whitespace character<\/td>\n<\/tr>\n
\\d<\/code><\/td>\nmatches any digit character, equiv. to [0-9]<\/code><\/td>\n<\/tr>\n
\\D<\/code><\/td>\nmatches any non-digit character<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

<\/a>Character sets: specialities inside [<\/code>…]<\/code><\/h2>\n

Different meanings<\/strong> apply inside a character set (\u201ccharacter class\u201d) denoted by [<\/code>…]<\/code> so that, instead of<\/strong> the normal rules given here, the following apply:<\/p>\n\n\n\n\n\n\n\n
[<\/code>characters<\/var>]<\/code><\/td>\nmatches any of the characters in the sequence<\/td>\n<\/tr>\n
[<\/code>x<\/var>-<\/code>y<\/var>]<\/code><\/td>\nmatches any of the characters from x<\/var> to y<\/var> (inclusively) in the ASCII code<\/td>\n<\/tr>\n
[\\-]<\/code><\/td>\nmatches the hyphen character\u00a0\u201c-<\/code>\u201d<\/td>\n<\/tr>\n
[\\n<\/code>]<\/td>\nmatches the newline; other single character denotations with\u00a0\\<\/code><\/a> apply normally, too<\/td>\n<\/tr>\n
[^<\/code>something<\/var>]<\/code><\/td>\nmatches any character except<\/em> those that [<\/code>something<\/var>]<\/code> denotes; that is, immediately after the leading \u201c[<\/code>\u201d, the circumflex \u201c^<\/code>\u201d means \u201cnot\u201d applied to all of the rest<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

<\/a>Examples<\/h2>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
expression<\/th>\nmatches…<\/th>\n<\/tr>\n
abc<\/code><\/td>\nabc<\/code> (that exact character sequence, but anywhere in the string)<\/td>\n<\/tr>\n
^abc<\/code><\/td>\nabc<\/code> at the beginning<\/em> of the string<\/td>\n<\/tr>\n
abc$<\/code><\/td>\nabc<\/code> at the end<\/em> of the string<\/td>\n<\/tr>\n
a|b<\/code><\/td>\neither of a<\/code> and b<\/code><\/td>\n<\/tr>\n
^abc|abc$<\/code><\/td>\nthe string abc<\/code> at the beginning or at the end of the string<\/td>\n<\/tr>\n
ab{2,4}c<\/code><\/td>\nan a<\/code> followed by two, three or four b<\/code>\u2019s followed by a c<\/code><\/td>\n<\/tr>\n
ab{2,}c<\/code><\/td>\nan a<\/code> followed by at least two b<\/code>\u2019s followed by a c<\/code><\/td>\n<\/tr>\n
ab*c<\/code><\/td>\nan a<\/code> followed by any number (zero or more) of b<\/code>\u2019s followed by a c<\/code><\/td>\n<\/tr>\n
ab+c<\/code><\/td>\nan a<\/code> followed by one or more b<\/code>\u2019s followed by a c<\/code><\/td>\n<\/tr>\n
ab?c<\/code><\/td>\nan a<\/code> followed by an optional b<\/code> followed by a c<\/code>; that is, either abc<\/code> or ac<\/code><\/td>\n<\/tr>\n
a.c<\/code><\/td>\nan a<\/code> followed by any single character (not newline) followed by a c<\/code><\/td>\n<\/tr>\n
a\\.c<\/code><\/td>\na.c<\/code> exactly<\/td>\n<\/tr>\n
[abc]<\/code><\/td>\nany one of a<\/code>, b<\/code> and c<\/code><\/td>\n<\/tr>\n
[Aa]bc<\/code><\/td>\neither of Abc<\/code> and abc<\/code><\/td>\n<\/tr>\n
[abc]+<\/code><\/td>\nany (nonempty) string of a<\/code>\u2019s, b<\/code>\u2019s and c\u2019s<\/code> (such as a<\/code>, abba<\/code>, acbabcacaa<\/code>)<\/td>\n<\/tr>\n
[^abc]+<\/code><\/td>\nany (nonempty) string which does not<\/em> contain any of a<\/code>, b<\/code> and c<\/code> (such as defg<\/code>)<\/td>\n<\/tr>\n
\\d\\d<\/code><\/td>\nany two decimal digits, such as 42<\/code>; same as \\d{2}<\/td>\n<\/tr>\n
\\w+<\/code><\/td>\na \u201cword\u201d: a nonempty sequence of alphanumeric characters and low lines (underscores), such as foo<\/code> and 12bar8<\/code> and foo_1<\/code><\/td>\n<\/tr>\n
100\\s*mk<\/code><\/td>\nthe strings 100<\/code> and mk<\/code> optionally separated by any amount of white space (spaces, tabs, newlines)<\/td>\n<\/tr>\n
abc\\b<\/code><\/td>\nabc<\/code> when followed by a word boundary (e.g. in abc!<\/code> but not in abcd<\/code>)<\/td>\n<\/tr>\n
perl\\B<\/code><\/td>\nperl<\/code> when not<\/em> followed by a word boundary (e.g. in perlert<\/code> but not in perl stuff<\/code>)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Examples of simple use in Perl statements<\/h3>\n

These examples use very simple regexps only. The intent is just to show contexts<\/em> where regexps might be used, as well as the effect of some \u201cflags\u201d to matching and replacements. Note in particular that matching is by default case-sensitive<\/em> (Abc<\/code> does not match abc<\/code> unless specified otherwise).<\/small><\/p>\n

s\/foo\/bar\/;<\/code>
\nreplaces the first<\/em> occurrence of the exact character sequence foo<\/code> in the \u201ccurrent string\u201d (in special variable $_<\/code>) by the character sequence bar<\/code>; for example, foolish bigfoot<\/code> would become barlish bigfoot<\/code><\/p>\n

s\/foo\/bar\/g;<\/code>
\nreplaces any<\/em> occurrence of the exact character sequence foo<\/code> in the \u201ccurrent string\u201d by the character sequence bar<\/code>; for example, foolish bigfoot<\/code> would become barlish bigbart<\/code><\/p>\n

s\/foo\/bar\/gi;<\/code>
\nreplaces any occurrence of foo<\/code> case-insensitively<\/em> in the \u201ccurrent string\u201d by the character sequence bar<\/code> (e.g. Foo<\/code> and FOO<\/code> get replaced by bar<\/code> too)<\/p>\n

if(m\/foo\/)<\/code>…
\ntests whether the current string contains the string foo<\/code><\/p>\n

Links: https:\/\/www.cs.tut.fi\/~jkorpela\/perl\/regexp.html<\/a>
\nhttp:\/\/www.troubleshooters.com\/codecorn\/littperl\/perlreg.htm<\/a>
\nhttp:\/\/www.skillz.ru\/dev\/php\/article-Regulyarnye_vyrazheniya_dlya_chaynikov.html<\/a>
\nhttp:\/\/www.ultraedit.com\/support\/tutorials_power_tips\/ultraedit\/non-greedy-perl-regex.html<\/a>
\nhttp:\/\/www.regular-expressions.info\/wordboundaries.html<\/a>
\nhttp:\/\/www.cs.xu.edu\/csci380\/99s\/perlstuff\/anchorreg.html<\/a>
\nhttp:\/\/www.tutorialspoint.com\/perl\/perl_regular_expression.htm<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Metacharacters char meaning ^ beginning of string $ end of string . any character except newline * match 0 or more times + match 1 or more times ? match 0 or 1 times; or: shortest match | alternative ( ) grouping; \u201cstoring\u201d [ ] set of characters { } repetition modifier \\ quote or […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[231],"tags":[32,198,199,28,14,11],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/posts\/638"}],"collection":[{"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/comments?post=638"}],"version-history":[{"count":3,"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/posts\/638\/revisions"}],"predecessor-version":[{"id":641,"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/posts\/638\/revisions\/641"}],"wp:attachment":[{"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/media?parent=638"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/categories?post=638"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/trichev.com\/blog\/wp-json\/wp\/v2\/tags?post=638"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}