Problem with Node.js and child_process.exec arguments

Question

On the command line, if I run

echo -n "foo" | openssl aes-128-cbc -k "key" -base64 -e

(the -n flag prevents echo from adding a newline to the end of its output), I get

U2FsdGVkX1+nMW5I4eZSasPKfsUuCpbFsnn56ngEdec=

But when I run

exec = require('child_process').exec;
exec('echo -n "foo" | openssl aes-128-cbc -k "key" -base64 -e', callback);

the callback gets the output

U2FsdGVkX1/CARBiGos0x9ALNhFqcIaFvZ9EUvVBxuc=

Why is it different? Decrypt it, and you'll get the string

-n foo

So somehow, exec encoded -n "foo" into "-n foo" (under Node 0.4.2).

Here's the weirdest part: I don't get this problem when I run my code directly from TextMate (via jashkenas' CoffeeScript bundle). At first I thought it was a path issue, but it isn't (making PATH identical in the two environments had no effect). Perhaps it's because one environment is a TTY and one isn't.

Are other folks aware of this inconsistency? Is this a Node bug, or am I ignoring something? I'm guessing that my problems will go away if I use the lower-level spawn instead of exec.

sarnold · Accepted Answer · 2011-03-19 01:21:49Z

3

Perhaps your /bin/echo doesn't respect -n? echo is frequently a shell builtin, and that one may respect -n. You may wish to use printf(1) instead, it is more portable.

answered Mar 19, 2011 at 1:21

sarnold

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3 Comments

Trevor Burnham Over a year ago

Hmm, /bin/echo -n "foo" seems to work as expected on the shell, so I still think the root cause is a problem with Node's exec. Thanks for the printf pointer, though—I was able to fix the problem with it.

sarnold Over a year ago

Trevor Burnham, if you figure out the root cause of your problem, I'd really like to know why your initial code didn't work as expected. But I'm glad you found a workaround that gets the job done.

davidchambers Over a year ago

I just ran into this myself. Could it be that Node is using /bin/sh rather than /bin/bash? From echo's man page: "Most notably, the builtin echo in sh(1) does not accept the -n option." In my case I simulated echo -n with echo foo | tr -d '\n'.

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