Let's see:

• use strict missing
• use warnings missing
• Missing my for $ifile, $ofile, $header, $data.
• no check that the program is called with the correct number of arguments
• Forking a shell (1) via qx (``) begs for trouble - see Improve pipe open?
• ... to run sed, just to read the first line of a file
• ... while making sed read the entire file
• ... and ignoring all quoting issues by simply not quoting at all - see The problem of "the" default shell
• ... and ignoring the fact that sed is not available by default on Windows and other operating systems
• Forking another shell via qx to pipe sed output to sort -u input
• ... again without any qouting
• ... again assuming sed is available everywhere
• ... assuming a POSIX sort is available everywhere. DOS/Windows sort does not understand -u and can't sort and filter out dupes
• ... reading the entire output of sort -u into memory
• ... just to write it out again three lines later
• And finally, exit 0 is redundant

This is highly inefficient and has several issues with "interesting" filenames.

In Re: Remove Duplicate Lines, BrowserUk explains how to use perl properly.

Another option - if running on a POSIX compatible system - is to use sort properly. Without headers, it is trivial:

sort -u < inputfile > outputfile
[download]

With headers, this will do:

head -n 1 inputfile > outputfile
sed '1d' inputfile | sort -u >> outputfile
[download]

This way, head can stop processing the input file after the first line, unlike sed -n '1p'. Directly writing to the outputfile avoids all further overhead of your script.

Alexander

(1) yes, given a sane filename, perl may start the first sed without help of the default shell. Change the filename to something interesting and perl will start sed via the default shell.