Noone yet has answered what the problem is witheyour original script you gave.

The problem is

1. it chops newlines but does not write them back. Change print FILECOPY; to print FILECOPY $_,$/;.
2. You did not chomp $std. This is neccessary as otherwise the regexp wont match.
3. It would be wise to change s/$_// to next.

4. Also the filename "/home/stdInfo" may be wrong.

5. Also arden says:

   For the examples that waswas-fng and pzbagel gave, if you attempt to delete student 12 (John), it will also delete users 120-129. . .

   That is also true for the original script in the question. So change /^$std/ to /^\Q$std\E\b/.

Apart from these your script is correct.