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perl

Practical Extraction and Reporting Language

Special Variables

  • "That thing": $_
  • Record Separator: $/

Techniques

Assign an array to some matches

@array_of_matches = ($source_string =~ m/..pattern../g);

Assign several variables to some matches

my ($num, $a, $t) = ($_ =~ m/([0-9]*)\. (.*) - (.*)\.mp3/) ;

Iterate a hash

while(($key, $value) = each(%$_)){
    print "$value is $key\n" ;
}

cat ~/.bash_history | perl -nle 'print "$.\t$_";'

This should probably be done with nl -ba .bash_history instead.

Edit a file in-place

To change all instances of "foo" to "bar":

perl -i -pe 's/foo/bar/g' filename.txt

Remove blank lines from a file

perl -pi -e "s/^\n//" file.txt

Remove lines from a file that match a certain regex

perl -i -pe 'if ($_ =~ m/string to remove/ ){$_ = "";}' filename.txt

Sort a line by spaces

See bash for a bash-only way

echo -n "whiskey tango foxtrot " \
| perl -e '
  $/=" " ;
  @foo = <STDIN> ;
  print (sort(@foo)) ;
  print "\n" ;
'

Sort records in a file that are separated by a blank line

##!/usr/bin/perl
$/ = "\n\n" ;
my @input = (<STDIN>) ;

my @sorted = sort { lc($a) cmp lc($b) } @input ;

foreach (@sorted) {
  if (length($_) > 10) { print "$_"; }
}

Subtract two from the last octet of a MAC address

for X in 24:b6:fd:ff:b7:f{{a..f},{0..9}} ; do
  echo -n "${X} - 2 = " ;
  echo ${X} \
  | perl -ne '
    @foo = split(":",$_) ;
    $foo[5] = sprintf("%02x", (hex($foo[5]) - 2)) ;
    $new = join(":",@foo) ;
    print "$new\n" ;
  ' ;
done ;

Add one to the last octet of a MAC address

for X in 24:b6:fd:ff:b7:c{{a..f},{0..9}} ; do
  echo ${X} \
  | perl -ne '
    @foo = split(":",$_) ;
    $foo[5] = sprintf("%02x", (hex($foo[5]) + 1)) ;
    $new = join(":",@foo) ;
    print "$new\n";
  ' ;
done ;