Well, here's the direct way. (samtregar suggests a more Perlish way, which will do much the same, in a possibly nicer way).

I created 2 files, <samp>cond-cpp</samp> and <samp>cond-prl</samp> which contain your codes. Neither ran <samp>-w</samp> or <samp>use strict</samp>; at least the latter will probably reduce the difference in execution time even further (<samp>cond-prl</samp>, however, runs the <samp>-P</samp> switch, for obvious reasons). 

<hal4 143 [15:07] ~/Perl/Test >time csh -c 'repeat 500 ./cond-prl >/de
+v/null'
0:17.75 elapsed, 14.410+3.200 user+system (99.2%), 0 (0+0) mem (avg. s
+hared+unshared stack), 152908 faults, 0/0 I/O
<hal4 144 [15:08] ~/Perl/Test >time csh -c 'repeat 500 ./cond-cpp >/de
+v/null'
0:16.55 elapsed, 11.630+7.200 user+system (113.7%), 0 (0+0) mem (avg. 
+shared+unshared stack), 431514 faults, 0/0 I/O

[download]
We see that <samp>cond-cpp</samp> finishes first, even though it takes more time to do so (to explain this, note that "113.7%" CPU utilization means we've got more than one processor). Load average was kept close to 0 (but this was not enforced in any way). Note also that the preprocessor method requires more system time -- it's starting a new process every time!

On a slower uniprocessor machine, we get 

<sylvie 113 [16:10] ~/Perl/Test >time csh -c 'repeat 500 ./cond-prl >/
+dev/null'
0:35.42 elapsed, 25.740+6.140 user+system (90.0%), 0 (0+0) mem (avg. s
+hared+unshared stack), 154646 faults, 0/0 I/O
<sylvie 114 [16:10] ~/Perl/Test >time csh -c 'repeat 500 ./cond-cpp >/
+dev/null'
0:39.19 elapsed, 16.490+18.530 user+system (89.3%), 0 (0+0) mem (avg. 
+shared+unshared stack), 462331 faults, 0/0 I/O

[download]
Here too the CPP method appears to have a slight edge.

Explanations? Only thing I can think of is "CPP is faster than Perl at doing this". Doubtless the real <samp>perl</samp> hackers out there can explain this.

Importance? Probably almost nil, unless you're starting a great many very short-lived processes.

In reply to Re: Preprocessor Pranks by ariels
in thread Preprocessor Pranks by cmilfo

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