$+ returns whatever the last bracket match matched. $& returns the entire matched string. ($0 used to return the same thing, but not any more.) $` returns everything before the matched string. $' returns everything after the matched string. Examples:
s/^([^ ]*) *([^ ]*)/$2 $1/; # swap first two words
if (/Time: (..):(..):(..)/) {
$hours = $1;
$minutes = $2;
$seconds = $3;
}
By default, the ^ character is only guaranteed to match at the beginning
of the string,
the $ character only at the end (or before the newline at the end)
and
perl
does certain optimizations with the assumption that the string contains
only one line.
The behavior of ^ and $ on embedded newlines will be inconsistent.
You may, however, wish to treat a string as a multi-line buffer, such that
the ^ will match after any newline within the string, and $ will match
before any newline.
At the cost of a little more overhead, you can do this by setting the variable
$* to 1.
Setting it back to 0 makes
perl
revert to its old behavior.
To facilitate multi-line substitutions, the . character never matches a newline (even when $* is 0). In particular, the following leaves a newline on the $_ string:
$_ = <STDIN>; s/.*(some_string).*/$1/; If the newline is unwanted, try one of s/.*(some_string).*\n/$1/; s/.*(some_string)[^\000]*/$1/; s/.*(some_string)(.|\n)*/$1/; chop; s/.*(some_string).*/$1/; /(some_string)/ && ($_ = $1);Any item of a regular expression may be followed with digits in curly brackets of the form {n,m}, where n gives the minimum number of times to match the item and m gives the maximum. The form {n} is equivalent to {n,n} and matches exactly n times. The form {n,} matches n or more times. (If a curly bracket occurs in any other context, it is treated as a regular character.) The * modifier is equivalent to {0,}, the + modifier to {1,} and the ? modifier to {0,1}. There is no limit to the size of n or m, but large numbers will chew up more memory.
You will note that all backslashed metacharacters in perl are alphanumeric, such as \b, \w, \n. Unlike some other regular expression languages, there are no backslashed symbols that aren't alphanumeric. So anything that looks like \\, \(, \), \<, \>, \{, or \} is always interpreted as a literal character, not a metacharacter. This makes it simple to quote a string that you want to use for a pattern but that you are afraid might contain metacharacters. Simply quote all the non-alphanumeric characters:
$pattern =~ s/(\W)/\\$1/g;