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?)//);