Linux Blog

Perl Regular Expression Cheat Sheet

Filed under: Shell Script Sundays — Owen at 10:15 pm on Saturday, October 6, 2007

Regular Expressions can be tricky, that’s why it is a good idea to keep a quick “cheat sheet” handy when working with them, here’s a concise cheat sheet to get you started:

.  	Match any character
\a  	Match alarm
\d 	Match digit character
\D  	Match non-digit character
\e  	Match escape
\f  	Match form-feed
\n  	Match newline
\r  	Match return
\s  	Match whitespace character
\S  	Match non-whitespace character
\t  	Match tab
\w 	Match "word" character (alphanumeric and "_")
\W  	Match non-word character
\022 Match octal char (i.e. 22 octal)
\xff  	Match hex char (i.e. ff in hex)
 
*	Match 0 or more times
+      	Match 1 or more times
?      	Match 1 or 0 times
 
{n}    	Match exactly n times
{n,}   	Match at least n times
{n,m}	  Match at least n but not more than m times
 
^	Match if at beginning
$ 	Match if at end
 
Examples:
\d{2}-\d{2}-\d{2}		# match date in dd-mm-yy format
^[ \t]+ 			#match leading whitespace
[ \t]+$			#match trailing whitespace
^[ \t]+|[ \t]+$ 		#match leading or trailing whitespace
 
$string =~ m/text/;		#returns true if $string contains text, case sensitive
$string =~ m/text$/i;		#returns true if $string contains text
$string =~ s/text1/text/;	#replace text1 with text2 in $string
$string !~ m/text/;		#returns false if $string contains text, case sensitive
$string !~ m/text/i;		#returns false if $string contains text

I find it useful to print it out and have it handy whenever I wade into the murky waters of regular expressions.





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