Inconsistent External Command Output

Question

The terminal transcript speaks for itself:

iMac:~$ echo -n a | md5
0cc175b9c0f1b6a831c399e269772661
iMac:~$ perl -e 'system "echo -n a | md5"'
c3392e9373ccca33629d82b17699420f

Note that the MD5 hash of a is 0cc175b9c0f1b6a831c399e269772661, the first result. Why does it turns out to be different when the same command is called by perl?

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By the way, perl is perl 5, version 12, subversion 4 (v5.12.4) built for darwin-thread-multi-2level. And the system: Mac OS 10.8, Darwin 12.0

Answer 1

When in the /bin/sh shell on mac, echo -n doesn't not print out the newline like it does in /bin/bash. You can see this if you drop into /bin/sh and run echo -n a, your output should look like this:

sh-3.2$ echo -n a
-n a

so you're literally getting -n a instead of the desired a. As perl system runs /bin/sh to evaluate your command, -n a is being passed into md5 instead of your desired a