Perl Cookbook

Regular Expression Grabbag

We have found these regular expressions useful or interesting.

Roman numbers

m/^m*(d?c{0,3}|c[dm])(l?x{0,3}|x[lc])(v?i{0,3}|i[vx])$/i

Swap first two words

s/(\S+)(\s+)(\S+)/$3$2$1/

Keyword = Value

m/(\w+)\s*=\s*(.*?)\s*$/             # keyword is $1, value is $2

Line of at least 80 characters

m/.{80,}/

MM/DD/YY HH:MM:SS

m|(\d+)/(\d+)/(\d+) (\d+):(\d+):(\d+)|

Changing directories

s(/usr/bin)(/usr/local/bin)g

Expanding %7E (hex) escapes

s/%([0-9A-Fa-f][0-9A-Fa-f])/chr hex $1/ge

Deleting C comments (imperfectly)

s{

    /\*                    # Match the opening delimiter

    .*?                    # Match a minimal number of characters

    \*/                    # Match the closing delimiter

} []gsx;

Removing leading and trailing whitespace

s/^\s+//;

s/\s+$//;

Turning \ followed by n into a real newline

s/\\n/\n/g;

Removing package portion of fully qualified symbols

s/^.*:://

Dotted quads (most IP addresses)

# XXX: fails on legal IPs 127.1 and 2130706433.
m{
        ^  ( \d | [01]?\d\d | 2[0-4]\d | 25[0-5] )
       \˙  ( \d | [01]?\d\d | 2[0-4]\d | 25[0-5] )
       \˙  ( \d | [01]?\d\d | 2[0-4]\d | 25[0-5] )
       \˙  ( \d | [01]?\d\d | 2[0-4]\d | 25[0-5] )
        $
    }x

Removing leading path from filename

s(^.*/)()

Extracting columns setting from TERMCAP

$cols = ( ($ENV{TERMCAP} || " ") =~ m/:co#(\d+):/ ) ? $1 : 80;

Removing directory components from program name and arguments

($name = " $0 @ARGV") =~ s,  /\S+/,  ,g;

Checking your operating system

die "This isn't Linux" unless $^O =~ m/linux/i;

Joining continuation lines in multiline string

s/\n\s+/ /g

Extracting all numbers from a string