Perl String Operation

A Perl String Operation is a string operation in a Perl Programming Language.

• Context:
  • It can be supported by a Perl Pattern Matching Expression.
• Example(s):
  • s/^([^ ]*) *([^ ]*)/$2 $1/
  • $string =~ s/(\w+)/\u\L$1/g;
• See: Perl Coding Notes, Perl Regular Expression, Perl Data Structure.

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References

2010

• (Melli, 2010) ⇒ Gabor Melli. (2010). “Perl String Operation - Examples."

Trim Whitespaces

  sub trim($) {
    my $string = shift;
    $string =~ s/^\s+|\s+$//g ;
    return $string;
  }

Swap first two words

   s/^([^ ]+([^ ]+)/$2 $1/;
   s/^([^ ]*) *([^ ]*)/$2 $1/;

Extract data from a fixed pattern

   if (/Time: (..):(..):(..)/) {
      $hours = $1 ;
      $mins = $2 ;
      $secs = $3 ;
   }

Extract all instances of a pattern within a line

    s/.*?(\[.+?\])*.*?/$1/g

    Example: echo "a[b]c[de]f[]g" | perl -ne 's/.*?(\[.+?\])*.*?/$1/g; print'
    ⇒ [b][de]

Pattern includes a variable

   # note that parentheses can be problematic.
   print "DEBUG: PROT skip if [$prot2] not in [$prot1] \n" if $debug>1 ;
   if ($prot1 !~ m/($prot2)/) {

Capitalize The First Letter

  $string = uc($string) ;

# capitalize the first letter of each space-separated word.
  $string =~ s/(\w+)/\u$1/g;

# capitalize the first letter of each space-separated word and lower case all others.
  $string =~ s/(\w+)/\u\L$1/g;

Count the number of items on a string

 $string="x-b   c-- de" ;

 # the number of dashes
 $countDashes = ($string =~tr/[^\-]//) ; 

 # the number of whitespaced tokens.
 $countTokens = () = (split(/\s+/,$string) ; 

Extract the text window surrounding an item ;

 $string="aa bb cc dd ee ff gg" ;

 # up to 4 characters before and two characters after
 $string =~ s/.*(.{0,4}dd.{0,2}).*/$1/ ;

Convert non-ASCII characters into SGML/HTML/XML-style decimal numeric character references (e.g. Ş becomes Ş)

s/([^\x00-\x7f])/sprintf("&#%d;", ord($1))/ge;'

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