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Asked: 2026-06-18T06:03:01+00:00

I’m trying this very basic thing, to output a random number: NUMBER=$[ ( $RANDOM

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I’m trying this very basic thing, to output a random number:

NUMBER=$[ ( $RANDOM % 500 )  + 1 ]; echo $NUMBER > /tmp/out

It runs fine directly on the CLI in Debian, but when I try to cron this, either as is:

* * * * * NUMBER=$[ ( $RANDOM % 500 )  + 1 ]; echo $NUMBER > /tmp/out

Or in part of a script in various ways, it consistently fails in my email alerts as:

/bin/sh: Syntax error: "(" unexpected

I’m very out of practice so I expect it’s something glaring obvious. I’ve tried every bracketing type combo I can think of with no luck. What am I missing?

The full mail alerts I received were:

From: Cron Daemon 
Sent: Friday, February 01, 2013 2:41 PM
Subject: Cron <root@host> NUMBER=$[ ( $RANDOM (failed)

/bin/sh: Syntax error: "(" unexpected
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1 Answer

  1. Editorial Team

    In addition to escaping the % sign, as F. Hauri points out, cron runs commands using /bin/sh, which doesn’t necessarily support all the features that bash does.

    * * * * * bash -c 'NUMBER=$[ ( $RANDOM \% 500 )  + 1 ]; echo $NUMBER > /tmp/out'

    Or better yet, put the command into a script with #!/bin/bash and execute the script from your crontab.

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