[PLUG] Need Explanation of BASH Script Error

John Sechrest sechrest at jas.peak.org
Sat Feb 18 16:44:38 UTC 2012


Look at your inputs. What happens if curl returns something with no data or
with random data in it. Especially if it has punctuation in it.

On Sat, Feb 18, 2012 at 8:13 AM, Rich Shepard <rshepard at appl-ecosys.com>wrote:

>   This morning my inbox contained a message from root generated when the
> hourly cron job ran at 4:00am:
>
> /home/rshepard/shell-scripts/ngetip.sh: line 4: [: !=: unary operator
> expected
>
>   Here are the first few lines of the script:
>
> #!/bin/bash
> OLDIP=$(cat /home/rshepard/CURRENTIP)
> NEWIP=$(curl -s http://automation.whatismyip.com/n09230945.asp)
> if [ $NEWIP != $OLDIP ];  then
>     echo $OLDIP
>     echo $NEWIP
>
>   This script has run for the past week plus without generating any errors.
> Looking in my ORA bash shell book the syntax for an if statement (using
> brackets to deliniate the if condition) seems correct. What might have
> caused this message to be generated?
>
> Rich
>
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>
>


-- 
John Sechrest
@sechrest
http://www.oomaat.com



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