Using the Perl chomp() function

Using the Perl chomp() function

Introduction

The chomp() function will remove (usually) any newline character from the end of a string. The reason we say usually is that it actually removes any character that matches the current value of $/ (the input record separator), and $/ defaults to a newline.

For more information on the $/ variable, try perldoc perlvar and see the entry for $/.

Example 1. Chomping a string

Most often you will use chomp() when reading data from a file or from a user. When reading user input from the standard input stream (STDIN) for instance, you get a newline character with each line of data. chomp() is really useful in this case because you do not need to write a regular expression and you do not need to worry about it removing needed characters.

When running the example below, using the enter key on a line by itself will exit the program.

  #!/usr/bin/perl
  use strict;
  use warnings;

  while (my $text = ) {
    chomp($text);
    print "You entered '$text'\n";
    last if ($text eq '');
  }

Example usage and output of this program is:

  a word
  You entered 'a word'
  some text
  You entered 'some text'

  You entered ''

Example 2. Chomping an array

If you chomp an array, it will remove a newline from the end of every element in the array:

  #!/usr/bin/perl
  use strict;
  use warnings;

  my @array = ("bob\n", "jill", "fred\n");

  print "Before chomp:\n";
  print "@array\n";

  chomp(@array);

  print "After chomp:\n";
  print "@array\n";

This program produces the following output:

  Before chomp:
  bob
   jill fred

  After chomp:
  bob jill fred

As you can see, the newlines have been removed from "bob" and "fred", but no characters have been removed from "jill".

Example 3. Chomping a hash

If you pass a hash into chomp(), it will remove newlines from every value (not key) of the hash:

  #!/usr/bin/perl
  use strict;
  use warnings;

  my %hash = (
    'first' => "one\n",
    'second' => "two\n",
    'third' => "three\n",
  );

  chomp(%hash);

  foreach my $k (keys %hash) {
    print "$k: $hash{$k} ";
  }

  print "\n";

  exit 0;

This program outputs:

  first: one second: two third: three