Here is a piece of code for you:

#!/usr/bin/perl -w 
use strict;
my $mode=shift @ARGV;
my $logfile=sprintf("/tmp/%s-env.txt",$mode);

open FOUT,"> $logfile" or die "$logfile: $!";
foreach my $key ( sort keys %ENV){
     printf FOUT "%s = \"%s\"\n",$key,$ENV{$key};
}
close FOUT;
system(sprintf "umask >> %s",$logfile);
system(sprintf "id >> %s",$logfile);
system(sprintf "pwd >> %s",$logfile);

exit(0);
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Don't forget to  $ chmod 755 /path/to/my/script/above.pl so it can run. First run it as a "batch" job

$ echo "/path/to/my/script/above.pl ascron" | at now
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which will be the same environment as a cronjob would be. Then run it from the command line:

$ /path/to/my/script/above.pl ascmdlin
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then check the differences:

diff /tmp/ascron-env.txt /tmp/ascmdlin-env.txt
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and that should help you rule some stuff out.

Typically the difference between command line and cron has to do with permissions or environment being different. It ain't rocket science.