Search for one command line parameter before the rest - bash

Question

I'm reading my command line parameters using getopt, and I'm reading a configuration file using .:
test.sh:
#!/bin/bash
set -- `getopt C:a:b:c: "$#"`
C="default.cfg"
. $C
while [ $# -gt 0 ]; do
case "$1" in
-a) cfg1="$2"; shift;;
-b) cfg2="$2"; shift;;
-c) cfg3="$2"; shift;;
-C) C="$2"; #you'll see what this is for later
shift;;
--) shift;
break;;
-*) echo "invalid option";
exit 1;;
*) break;;
esac
shift
done
echo "cfg1 = $cfg1"
echo "cfg2 = $cfg2"
echo "cfg3 = $cfg3"
exit 0
default.cfg::
cfg1=hello
cfg2=there
cfg3=friend
This all works as expected:
$ ./test.sh
cfg1 = hello
cfg2 = there
cfg3 = friend
$ ./test.sh -b optional
cfg1 = hello
cfg2 = optional
cfg3 = friend
This issue is I want configurations to be prioritized in the following manner:
options given on the command line
options defined in the config file defined by the -C option
options defined in the default config file
So if I have this:
test.cfg:
cfg1=custom_file_1
cfg2=custom_file_2
I want to get this:
$ ./test.sh -b command_line -C test.cfg
cfg1 = custom_file_1
cfg2 = command_line
cfg3 = friend
I just can't figure out how to load the default config file, then search the options for -C, then load the custom config file, overwriting the default, then search the command line parameters AGAIN and overwrite the configs again. I'm pretty new to shell scripting, so forgive me if I'm missing something obvious.

Answer 1

You can preprocess the arguments and pull out the value you're looking for:
#!/bin/bash
args=$(getopt C:a:b:c: "$#")
eval set -- $args
conf="default.cfg"
source "$conf"
# pre-process the arguments and see if we can find -C
found=0
for opt in "$#"; do
if [[ $found -eq 1 ]] && [[ -f "$opt" ]]; then
source "$opt"
break
fi
if [[ "$opt" == "-C" ]]; then
found=1
fi
done
while [ $# -gt 0 ]; do
case "$1" in
-a) cfg1="$2"; shift;;
-b) cfg2="$2"; shift;;
-c) cfg3="$2"; shift;;
-C) shift;; #don't do anything with this
--) shift;
break;;
-*) echo "invalid option";
exit 1;;
*) break;;
esac
shift
done
echo "cfg1 = $cfg1"
echo "cfg2 = $cfg2"
echo "cfg3 = $cfg3"
exit 0

Answer 2

To overwrite variables, try to replace :
-C) C="$2";
with :
-C) . "$2";
And invoke it with :
./test.sh -C test.cfg -a command_line1 -b command_line2
Update :
For options in any order, you can try this :
C="default.cfg"
. $C
while getopts C:a:b:c: OPTION
do
case $OPTION in
a) cfg1_override=$OPTARG;;
b) cfg2_override=$OPTARG;;
c) cfg3_override=$OPTARG ;;
C) . $OPTARG;;
-) break;;
-*) echo "invalid option";
exit 1;;
*) break;;
esac
done
shift $(($OPTIND - 1))
cfg1="${cfg1_override-${cfg1}}"
cfg2="${cfg2_override-${cfg2}}"
cfg3="${cfg3_override-${cfg3}}"
echo "cfg1 = $cfg1"
echo "cfg2 = $cfg2"
echo "cfg3 = $cfg3"
exit 0
Based on Is it possible to specify the order getopts conditions are executed?

Answer 3

First source default.cfg.
Than scan your options for a -C option. Handle this one when found.
Finally use getopts and skip -C when you find it during getopts.