Your best choices for collecting output from a program are using backticks `` or the open call.

$output=`tar -tf`;  #collects all the output from the "tar -tf" comman
+d
open TAR, "tar -tf|"; #open a process with a pipe on the right side
while(<TAR>){ #get the output line by line into $_; 
   do_something($_); #process the results;   
}
close TAR;
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