But the "or die" part is wrong: system() will return the exit status of the process, which is based on shell semantics: a return value of zero means "success" (i.e. "good") whereas any non-zero value means "failure" (i.e. "bad") -- so you probably want to say "and die" instead. But that's confusing, so it's usually better to say it like this:

my $err_stat = system( $prog, @args );
die "system failed on $prog @args: $?" if $err_stat;
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As to the reason for the multi-arg usage, the difference between this:

system( "$prog @args" );
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system( $prog, @args );
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In the multi-arg usage (the latter choice), each element of @args is passed directly to the "argv" array of "cat" -- if an arg does not map to a readable file name, cat reports an error. In the single-string command-line case, the whole string is passed to a shell, and the shell executes the string. If the string happens to contain workable instructions that you don't expect or don't want, you could be in for a nasty surprise.

Hi,

But the "or die" part is wrong: system() will return the exit status of the process, which is based on shell semantics: a return value of zero means "success" (i.e. "good") whereas any non-zero value means "failure" (i.e. "bad") -- so you probably want to say "and die" instead.

You are wrong, the example is fine.

system('procheck', $pdbfile, '1.0') == 0 or die "system failed ( $? )"
+;
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die is only called, if the returncode from system is not 0. This is exactly what we want it to do.
Boris