As others here said (hippo) you need to clarify whether it happens with the same file all the time.

You say:

The script seems to be working okay when XMLList.txt contains, say 10-15 lines.

Anything more and perl script seems to abruptly stop parsing half-way and the shell script (which calls the perl script) returns a "27000838 Segmentation fault(coredump)" error.

But maybe there is a bad file half-way the list which is never processed when you process the first 10-15 files.

So, modify your code to print the filename each time, and also the number of files processed to ease you like:

my $fcount = 1;
while (my $xmlfile = <$list>) {
    chomp $xmlfile;
    print STDERR "$0 : about to process file # $fcount = '$xmlfile'\n"
+;
    $twig->parsefile($xmlfile);
    print STDERR "$0 : file $xmlfile' processed OK.\n";
    $fcount++;
}
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Note: it is not either bugs or bad file(s). It could be bugs and bad file(s)