how to read a config variable into a script?

[matonb]

What's the best way to read a value from a configuration file into a script?

I'm trying to get the command_file vaule from nagios.cfg into a script, this works but what's the best way to do it?

command_file=$(perl -F= -lane 'print $F[1] if /^[[:space:]]*command_file[[:space:]]*=/' /etc/nagios/nagios.cfg)

[meton_magis]

if it works, why do you need a better way to do it?

is there a specific bottleneck you need to avoid?

[matonb]

There's never any harm in trying to improve your techniques or methods.

I'm also fairly sure that there is a better way to achieve this goal

[meton_magis]

but what about it are you changing? does it take a long time to run? does it use too much ram? you need to be more specific.

anything that works is perfect unless there is a reason to improve it. There is no BEST way to do something. just a correct way and a wrong way.

[Kloschüssel]

you could (if you can) change the config file to be a bash script and just invoke it.

config file:

VAR="bla"

script:

./config.cfg
echo $VAR

the combination should produce the output

#$ ./script.sh
bla

[sixdrift]

I often create config files using BASH variable syntax and then source them into the running script. This works because if you execute a config var script, it runs in a subshell process and the results are not propagated back to the parent process. But if you source it, you are adding it to your current process environment.

config file:

#!/bin/bash
var1="some value"
var2=42

script file:

#!/bin/bash
$HOME/debug/junk.conf
echo "var1 is $var1"
echo "var2 is $var2"
source $HOME/debug/junk.conf
echo "var1 is $var1"
echo "var2 is $var2"

Output:

var1 is 
var2 is 
var1 is some value
var2 is 42

Now if you have an existing config file that you cannot control the format of, pre-process it and produce an output file in /tmp that you can source. Then when you are done, delete your temp. In this way, you can massage the config file to remove unnecessary items or even change some using combinations of text processing commands (sed, cut, ...) and only source the bits that are needed.