Difference between revisions of "Regular Expressions"
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|*||0 or more matches of previous expression||( )||Subexpression | |*||0 or more matches of previous expression||( )||Subexpression | ||
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− | |<nowiki>+</nowiki>||1 or more matches of previous expression||[ ]||Match | + | |<nowiki>+</nowiki>||1 or more matches of previous expression||[ ]||Match any of the characters between the [ ].<br>^as first character negates the match |
|- | |- | ||
|<nowiki>?</nowiki>||0 or 1 matches of previous expression.<br>Stop search as soon as next expression is found (non greedy) | |<nowiki>?</nowiki>||0 or 1 matches of previous expression.<br>Stop search as soon as next expression is found (non greedy) |
Revision as of 20:52, 29 August 2018
Regular expressions or regexp are used to find strings in text.
. | Any character except newline | \c | Control character |
\d | Digit | \D | non Digit |
\s | Whitespace | \S | non Whitespace |
\w | Word character [A-Za-z0-9] | \W | non Word character |
^ | Start of string | $ | End of string |
* | 0 or more matches of previous expression | ( ) | Subexpression |
+ | 1 or more matches of previous expression | [ ] | Match any of the characters between the [ ]. ^as first character negates the match |
? | 0 or 1 matches of previous expression. Stop search as soon as next expression is found (non greedy) |
Perl
- perl -lne 'print $1 if (/<regexp(subexp)>/)'
- Commandline to print the first subexp in a match.
- $var =~ /<pattern>/
- Generic syntax, this expression is true if the pattern is matched in $var
- @array = $var =~ m/<pattern>/g;
- Put all matches (or all first submatches) of <pattern> in var into @array
Following variables are when a match is made:
- $&
- Contains the string matched by the last pattern match
- $`
- The string preceding whatever was matched by the last pattern match, not counting patterns matched in nested blocks that have been exited already.
- $'
- The string following whatever was matched by the last pattern match, not counting patterns matched in nested blocks that have been exited already.
Example:
$_ = 'abcdefghi';
/def/;
print "$`:$&:$'";
# prints abc:def:ghi
- $1
- String matched by the first subexpression.
- $+
- The last bracket matched by the last search pattern. This is useful if you don't know which of a set of alternative patterns matched.
Example:
/Version: (.*)|Revision: (.*)/
&& ($rev = $+);