CODEWITHSUNDEEP
regexperl
Runner
Runner

Reputation: 375

please explain this regular expression

  ^[[:space:]]*@

I can't figure out what the [[:space:]]* means in the above regular expression. Please help, thanks!

Upvotes: 1

Views: 153

Answers (3)

tadman
tadman

Reputation: 211570

There are a number of ways of expressing things like "whitespace character", and this is one of them. The set [...] allows the inclusion of things like [:space:] to add space characters to the set.

This reads as:

^ # At the beginning of string...
[[:space:]]* # ...zero or more whitespace characters...
@ # ...followed by an at sign.

Upvotes: 0

Bill
Bill

Reputation: 5762

[:space:] is a POSIX character class which matches All whitespace characters, including line breaks in the word.

In other words [:space:] is identical to \s (since Perl 5.18[1])

http://www.regular-expressions.info/posixbrackets.html

  1. Before 5.18, the vertical tab (U+000B) wasn't included in \s.

    $ diff -u <( unichars -au '\s' ) <( unichars -au '[[:space:]]' ) \
    && echo 'no difference'
--- /dev/fd/63  2013-05-21 22:08:03.000000000 -0400
+++ /dev/fd/62  2013-05-21 22:08:03.000000000 -0400
@@ -1,5 +1,6 @@
  ---- U+00009 CHARACTER TABULATION
  ---- U+0000A LINE FEED (LF)
+ ---- U+0000B LINE TABULATION
  ---- U+0000C FORM FEED (FF)
  ---- U+0000D CARRIAGE RETURN (CR)
  ---- U+00020 SPACE

Upvotes: 9

Platinum Azure
Platinum Azure

Reputation: 46183

This is a POSIX character class, in this case a Unicode-friendly way of representing "any whitespace character".

See this page, scroll down to "POSIX Character Classes".

Upvotes: 4

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