Perl Regular Expressions
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; "storing" [ ] set of characters { } repetition modifier quote or special
Repetition
a* zero or more a's
a+ one or more a's
a? zero or one a's (i.e., optional a)
a{m} exactly m a's
a{m,} at least m a's
a{m,n} at least m but at most n a's repetition?
t tab
n newline
r return (CR)
xhh character with hex. code hh
b "word" boundary
B not a "word" boundary
w matches any single character classified as a
"word" character (alphanumeric or _)
W matches any non-"word" character
s matches any whitespace character (space, tab, newline)
S matches any non-whitespace character
d matches any digit character, equiv. to [0-9]
D matches any non-digit character
[characters] matches any of the characters in the sequence
[x-y] matches any of the characters from x to y
(inclusively) in the ASCII code
[-] matches the hyphen character -
[n] matches the newline; other single character
denotations with apply normally, too
Examples
How do I extract everything between a the words “start” and “end”?
$mystring = “The start text always precedes the end of the end text.”;
if($mystring =~ m/start(.*)end/) {
print $1;
}
How do I extract a complete number, like the year?
$mystring = “[2004/04/13] The date of this article.”;
if($mystring =~ m/(d+)/) {
print “The first number is $1.”;
}
# find word that is bolded
# returns: $1 = ‘text’
$line = “This is some text with HTML and “;
$line =~ m/(.*)/i;