I'm writing a bash script to modify a config file which contains a bunch of key/value pairs. How can I read the key and find the value and possibly modify it?
A wild stab in the dark for modifying a single value:
sed -c -i "s/\($TARGET_KEY *= *\).*/\1$REPLACEMENT_VALUE/" $CONFIG_FILE
assuming that the target key and replacement value don't contain any special regex characters, and that your key-value separator is "=". Note, the -c option is system dependent and you may need to omit it for sed to execute.
For other tips on how to do similar replacements (e.g., when the REPLACEMENT_VALUE has '/' characters in it), there are some great examples here.