6.23. 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/^.*:://
IP address
m/^([01]?\d\d|2[0-4]\d|25[0-5])\.([01]?\d\d|2[0-4]\d|25[0-5])\.
   ([01]?\d\d|2[0-4]\d|25[0-5])\.([01]?\d\d|2[0-4]\d|25[0-5])$/;
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
@nums = m/(\d+\.?\d*|\.\d+)/g;
Finding all-caps words
@capwords = m/(\b[^\Wa-z0-9_]+\b)/g;
Finding all-lowercase words
@lowords = m/(\b[^\WA-Z0-9_]+\b)/g;
Finding initial-caps word
@icwords = m/(\b[^\Wa-z0-9_][^\WA-Z0-9_]*\b)/;
Finding links in simple HTML
@links = m/<A[^>]+?HREF\s*=\s*["']?([^'" >]+?)[ '"]?>/sig;
Finding middle initial in $_
($initial) = m/^\S+\s+(\S)\S*\s+\S/ ? $1 : "";
Changing inch marks to quotes
s/"([^"]*)"/``$1''/g
Extracting sentences (two spaces required)
{ local $/ = "";
  while (<>) {
    s/\n/ /g;
    s/ {3,}/  /g;
    push @sentences, m/(\S.*?[!?.])(?=  |\Z)/g;
  }
}
YYYY-MM-DD
m/(\d{4})-(\d\d)-(\d\d)/            # YYYY in $1, MM in $2, DD in $3
North American telephone numbers
m/ ^
      (?:
       1 \s (?: \d\d\d \s)?            # 1, or 1 and area code
       |                               # ... or ...
       \(\d\d\d\) \s                   # area code with parens
       |                               # ... or ...
       (?: \+\d\d?\d? \s)?             # optional +country code
       \d\d\d ([\s\-])                 # and area code
      )
      \d\d\d (\s|\1)                   # prefix (and area code separator)
      \d\d\d\d                         # exchange
        $
 /x
Exclamations
m/\boh\s+my\s+gh?o(d(dess(es)?|s?)|odness|sh)\b/i
Extracting lines regardless of line terminator
push(@lines, $1)
    while ($input =~ s/^([^\012\015]*)(\012\015?|\015\012?)//);