How do I evaluate shell variables in a string?

Question

In my Perl script I get strings of file paths that may contain environment variables, e.g. $FONTS/test.ttf or $TMP/file.txt.

I now want to open those files like this:

open my $handle, "<$filename" or die $!;

How can I now expand the environment variables prior to the open call, as e.g. the bash shell would do?

Answer 1

You can make use of backticks as:

$filename = `echo \$FONTS/test.ttf`; # $filename will now be /dir/to/fonts/test.ttf
open( FILE1, "<$filename" ) or die;

Answer 2

If the environmental variables are set, you can use a simple substitution:

$filename =~ s/\$(\w+)/$ENV{$1}/g;