$FILE="/etc/mnttab";
open FILE or die "Can't open $FILE: $!";
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Wow. I learn something new everyday: the one-argument form of open:

If EXPR is omitted, the global (package) scalar variable of the same name as the FILEHANDLE contains the filename.

Update: see also Single Argument Open

---

        push @mnttab, ($lv, $fs)
}
%mnttab = @mnttab;
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You can eliminate the array as follows:

        $mnttab{$lv} = $fs;
}
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See also:

• use strict and warnings