When you put that string into the system call, you have to escape the "$" in and the backslashes in the sed args:

system( "cat text.txt|wc -l| sed 's/^[ \\t]*//'|sed 's/[ \\t]*\$//'" )
+;
[download]

(not tested). The point is that perl will interpolate "\t" and "$/" before they go to the shell, unless you put the necessary escapes in the perl script.

Curiously, I don't see anything being done with the results of that command line. If you were intending to use the output in your perl script, you should be using backticks. Otherwise, you should be redirecting the output to some file or something.

Anyway, why not save yourself all that shell overhead, and do those operations with perl code instead of sed?

(updated to remove extraneous code tag and fix spelling errors)