I need to check the last character of a sting. It needs to be \ or I have to add it.

I wrote a function some time ago which solved a more general problem: uncomp($s,$tail) returns $s if it already ends in $tail, and returns $s.$tail otherwise. In my case, I more often needed it to ensure that the string is ended in a newline, so I made this as a default: unchomp($s) is equivalent to unchomp($s,"\n"), but of course you can easily adapt this to your path separator.

sub unchomp {
  my ($s,$suffix) = (@_,"\n");
  die("unchomp called on undef string") unless defined($s);
  die("unchomp called for undef suffix") unless defined($suffix);
  my $slen=length($suffix);
  substr($s,-$slen) eq $suffix ? $s : ($s.$suffix)
}
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