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up vote 3 down vote favorite

I just want to return true or false if a service is running. Here is where I'm at, not first try or last but current at writing:

service iptables status | grep -qi "not running"

The sdtout for service iptables status when it's stopped is iptables: Firewall is not running When I run what I came up with is nothing on a new line, which I guess is not unexpected as 0 is true and non-0 is false. So, I need to test to ensure it works, but I'm unsure what to do. Here is the try:

service iptables status | grep -qi "not running" || echo "stopped"

so when the service is stopped I expected to see stopped but I didn't get anything but a new line.

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2 Answers

up vote 2 down vote accepted 
service iptables status | grep -qi "not running" && echo "stopped"

You just need to replace || with &&. One confusing thing about shell scripting is that 0 is true and any other number is false, opposite to most other languages. This is just because programs generally return a 0 for success.

I also need to add an 2>&1 after status as service on my distro outputs to stderr, doesn't look like its a problem for you though.

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IMHO better to think of it as exit status and not boolean true / false. Thus if exit status == EXIT_SUCCESS then …. Grep also only uses 1 for non-match. Anything > 1 is error code. –  Sukminder Jan 11 at 10:07
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Sure, but sooner or later you have to use true or false builtins for something. Although succeed and fail may be more intuitive names for them :) –  Graeme Jan 11 at 11:49
    
No. true and false are boolean values. My point, perhaps poorly conveyed, is that exit status is not a boolean value. It evaluates to true and false, but the value falls between 0 and 255. We also have ((1)) and ((0)). –  Sukminder Jan 12 at 1:55
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up vote 1 down vote

If grep does not see a match, it will return a non-zero code. A return of 0 means that a match was found. You probably want:

service iptables status | grep -qi 'not running' && echo 'Stopped'
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