To expound a bit on dws's remarks: you would not want to run that system call if the value of $file1 was something like "/dev/null;rm -rf *"... The point would be to make sure that the variables being used are not so "weird" as to wreak havoc when they are passed "successfully" to the shell.

To be safe, the values of $program1, $program2, etc. would be "known", drawn from some limited set of alternatives, and the values of $file1, $file2 would be pre-conditioned to eliminate any characters that would cause problems in the shell (esp. semicolons, pipe symbols, ampersands and such) -- either remove them outright or replace them with safe punctuation characters, underscores, or whatever.

But if you need to handle some oddball file names, you might try the following alternative to the system call: 

$file1 = s/(\W)/\\$1/; # and similarly for other filenames
open( SH, "| /bin/sh");
print SH "$program1 $file1 | $program2 | $program3 > $file2\n";
close SH;

[download]
I'm not saying this is guaranteed to work for you, but it's something to try (especially if you were intending to use the system call inside a loop: open the shell before going into the loop, then just print a command line to the shell on each iteration -- see a sample of this in a utility I posted a while ago).

In reply to Re: system, pipes, shell, quoting by graff
in thread system, pipes, shell, quoting by superpete

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