Why does my Perl script fail on "~/" but works with "$ENV{HOME}"?

Question

I have been using this script of mine FOREVER and I have always been using "~/" to expand my home directory. I get into work today and it stopped working:

#if ( $output   eq "" ) { $output   = "~/tmp/find_$strings[0].rslt" } # BROKEN
if ( $output   eq "" ) { $output   = "$ENV{HOME}/tmp/find_$strings[0].rslt" } #WORKS
 ...
open OUT_FILE, ">$output" or die "cant open $output : $!";

Any ideas about why this would suddenly stop worrking?

Error looks like:

cant open stephen/tmp/find_coverp.rslt : No such file or directory at /user/stephen/bin/find.pl line 137.

Answer 1

~ is expanded by the shell. Perl has no idea about it. So, it would work only within a shell script.

Answer 2

The tilde expansion is not done by perl, it is done by the shell.

You should instead use:

 use File::Spec::Functions qw( catfile );
 ...
 my $fn = catfile $ENV{HOME}, 'tmp', "find_$strings[0].rslt";
 ...
 open my $out, '>', $fn or die "Cannot open '$fn': $!";

Answer 3

As stated by prior answer, "~" (tilde) is expanded by shell, not perl. Most likely, it was working due to existence of a directory "~" in your current directory, which eventually got removed, leading to the bug surfacing:

To illustrate:

1. Tilde not working in Perl, using $ENV{HOME} works:

   $ echo MM > MM
   $ perl5.8 -e '{print `cat ~/MM`}'
   cat: cannot open ~/MM
   $ perl5.8 -e '{print `cat $ENV{HOME}/MM`}'
   MM
   

2. Making the tilde-named directory works:

   $ mkdir \~
   $ echo MM > \~/MM
   $ ls -l \~
   -rw-rw-r--   1 DVK users          3 Jun 10 15:15 MM
   $ perl5.8 -e '{print `cat ~/MM`}'         
   MM
   

3. Removing it restores the error, as you observed:

   $ /bin/rm -r \~
   $ ls -l \~
   ~: No such file or directory
   $ perl5.8 -e '{print `cat ~/MM`}'
   cat: cannot open ~/MM
   

This offers a plausible explanation, though I'm not 100% there can't be others.