Modify config file using bash script - bash

Question

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?

Answer 1

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.

Answer 2

Hope this helps someone. I created a self contained script, which required config processing of sorts.
#!/bin/bash
CONFIG="/tmp/test.cfg"
# Use this to set the new config value, needs 2 parameters.
# You could check that $1 and $2 is set, but I am lazy
function set_config(){
sudo sed -i "s/^\($1\s*=\s*\).*\$/\1$2/" $CONFIG
}
# INITIALIZE CONFIG IF IT'S MISSING
if [ ! -e "${CONFIG}" ] ; then
# Set default variable value
sudo touch $CONFIG
echo "myname=\"Test\"" | sudo tee --append $CONFIG
fi
# LOAD THE CONFIG FILE
source $CONFIG
echo "${myname}" # SHOULD OUTPUT DEFAULT (test) ON FIRST RUN
myname="Erl"
echo "${myname}" # SHOULD OUTPUT Erl
set_config myname $myname # SETS THE NEW VALUE

Answer 3

Assuming that you have a file of key=value pairs, potentially with spaces around the =, you can delete, modify in-place or append key-value pairs at will using awk even if the keys or values contain special regex sequences:
# Using awk to delete, modify or append keys
# In case of an error the original configuration file is left intact
# Also leaves a timestamped backup copy (omit the cp -p if none is required)
CONFIG_FILE=file.conf
cp -p "$CONFIG_FILE" "$CONFIG_FILE.orig.`date \"+%Y%m%d_%H%M%S\"`" &&
awk -F '[ \t]*=[ \t]*' '$1=="keytodelete" { next } $1=="keytomodify" { print "keytomodify=newvalue" ; next } { print } END { print "keytoappend=value" }' "$CONFIG_FILE" >"$CONFIG_FILE~" &&
mv "$CONFIG_FILE~" "$CONFIG_FILE" ||
echo "an error has occurred (permissions? disk space?)"

Answer 4

sed "/^$old/s/\(.[^=]*\)\([ \t]*=[ \t]*\)\(.[^=]*\)/\1\2$replace/" configfile

Answer 5

So I can not take any credit for this as it is a combination of stackoverflow answers and help from irc.freenode.net #bash channel but here are bash functions now to both set and read config file values:
# https://stackoverflow.com/a/2464883
# Usage: config_set filename key value
function config_set() {
local file=$1
local key=$2
local val=${#:3}
ensureConfigFileExists "${file}"
# create key if not exists
if ! grep -q "^${key}=" ${file}; then
# insert a newline just in case the file does not end with one
printf "\n${key}=" >> ${file}
fi
chc "$file" "$key" "$val"
}
function ensureConfigFileExists() {
if [ ! -e "$1" ] ; then
if [ -e "$1.example" ]; then
cp "$1.example" "$1";
else
touch "$1"
fi
fi
}
# thanks to ixz in #bash on irc.freenode.net
function chc() { gawk -v OFS== -v FS== -e 'BEGIN { ARGC = 1 } $1 == ARGV[2] { print ARGV[4] ? ARGV[4] : $1, ARGV[3]; next } 1' "$#" <"$1" >"$1.1"; mv "$1"{.1,}; }
# https://unix.stackexchange.com/a/331965/312709
# Usage: local myvar="$(config_get myvar)"
function config_get() {
val="$(config_read_file ${CONFIG_FILE} "${1}")";
if [ "${val}" = "__UNDEFINED__" ]; then
val="$(config_read_file ${CONFIG_FILE}.example "${1}")";
fi
printf -- "%s" "${val}";
}
function config_read_file() {
(grep -E "^${2}=" -m 1 "${1}" 2>/dev/null || echo "VAR=__UNDEFINED__") | head -n 1 | cut -d '=' -f 2-;
}
at first I was using the accepted answer's sed solution: https://stackoverflow.com/a/2464883/2683059
however if the value has a / char it breaks

Answer 6

in general it's easy to extract the info with grep and cut:
cat "$FILE" | grep "^${KEY}${DELIMITER}" | cut -f2- -d"$DELIMITER"
to update you could do something like this:
mv "$FILE" "$FILE.bak"
cat "$FILE.bak" | grep -v "^${KEY}${DELIMITER}" > "$FILE"
echo "${KEY}${DELIMITER}${NEWVALUE}" >> "$FILE"
this would not maintain the order of the key-value pairs obviously. add error checking to make sure you don't lose your data.

Answer 7

I have done this:
new_port=$1
sed "s/^port=.*/port=$new_port/" "$CONFIG_FILE" > /yourPath/temp.x
mv /yourPath/temp.x "$CONFIG_FILE"
This will change port= to port=8888 in your config file if you choose 8888 as $1 for example.

Answer 8

Suppose your config file is in below format:
CONFIG_NUM=4
CONFIG_NUM2=5
CONFIG_DEBUG=n
In your bash script, you can use:
CONFIG_FILE=your_config_file
. $CONFIG_FILE
if [ $CONFIG_DEBUG == "y" ]; then
......
else
......
fi
$CONFIG_NUM, $CONFIG_NUM2, $CONFIG_DEBUG is what you need.
After your read the values, write it back will be easy:
echo "CONFIG_DEBUG=y" >> $CONFIG_FILE