epoch=$(perl -MFile::stat -e "print stat('$list')->mtime")

I would guess that $list contains special characters that are preventing correct interpolation. Try:

epoch=$(perl -MFile::stat -se 'print stat($list)->mtime' -- -list="$li
+st")
# or, better:
epoch=$(perl -MFile::stat -wMstrict '-Mvars=$list' -se 'print stat($li
+st)->mtime' -- -list="$list")
[download]

See perlrun for the -s switch. Of course, the very best way is to rewrite your entire bash script as a Perl script. And why does your bash script start with use strict;? For bash scripts, see Safer bash scripts with set -euxo pipefail.