merges multiple lines based on first field

uniq-j.pl

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

my $DELIM = shift || ' ';

my $last;
my @stash;

while (<STDIN>)
{
  chomp;
  my @line = split /$DELIM/;
  my $field = shift @line;

  unless (defined $last and $field eq $last)
  {
    print "\n" if defined $last;
    undef $last;
  }
  print $last ? $DELIM : $field . $DELIM;

  print join $DELIM, @line;
  $last = $field;
}
print "\n"

example input:

foo bar
foo baz
foo bla fasel
foo ranz
bla blub
bla ipsum
bla temp foobar

example output (cat uniq-j.txt | ./uniq-j.pl):

foo bar baz bla fasel ranz
bla blub ipsum temp foobar