Ubuntu – Best way to read a config file in bash

bash

What is the best way to read a config file in bash?
For example, you have a script and aren't willing to fill in all the config manually each time you call the script.

Edit 1:
I think I didn't make it clear, so: what I want is… I have a configfile which is like

variable_name value  
variable_name value ...

and I want to read that. I know I could just grep it for the arguments I'm looking for or so… but maybe there's a more intelligent way 🙂

Best Answer

As mbiber said, source another file. For example, your config file (say some.config) would be:

var1=val1
var2=val2

And your script could look like:

#! /bin/bash

# Optionally, set default values
# var1="default value for var1"
# var1="default value for var2"

. /path/to/some.config

echo "$var1" "$var2"

The many files in /etc/default usually serve as configuration files for other shell scripts in a similar way. A very common example from posts here is /etc/default/grub. This file is used to set configuration options for GRUB, since grub-mkconfig is a shell script that sources it:

sysconfdir="/etc"
#…
if test -f ${sysconfdir}/default/grub ; then
  . ${sysconfdir}/default/grub
fi

If you really must process configuration of the form:

var1 some value 1
var2 some value 2

Then you could do something like:

while read var value
do
    export "$var"="$value"
done < /path/to/some.config

(You could also do something like eval "$var=$value", but that's riskier than sourcing a script. You could inadvertently break that more easily than a sourced file.)

Related Solutions

Ubuntu – Bash always evaluate Regex as true

I was too quick on this one, your test works. I suspect you somehow have set $SCREEN_NAME either globally or previously in the script as a string containing an illegal character.

^[a-zA-Z0-9_.-]+$ matches a non-NULL string containing only the allowed characters, so if $SCREEN_NAME is a non-NULL string containing only the allowed characters, $SCREEN_NAME =~ ^[a-zA-Z0-9_.-]+$ 's value is 0.

! inverts its value, so if $SCREEN_NAME is a non-NULL string containing only the allowed characters, ! [[ $SCREEN_NAME =~ ^[a-zA-Z0-9_.-]+$ ]]'s value is 1.

So the condition is ok.

Run echo $SCREEN_NAME in both bash and your script and check whether the actual output matches what's expected.

Edit: To remove the trailing carriage return, one solution is to pipe grep's output to tr before cut:

SCREEN_NAME=$(grep -i 'server_screen_title' server.properties | tr -d '\r' | cut -f2 -d'=')

Ubuntu – What’s the best way to transform a string into an associative array

I would do this just using bash itself:

#!/bin/bash
read -e -p 'Enter the string: ' post
declare -A myArr

while IFS='&' read name age; do
    myArr["${name##*=}"]="${age##*=}"
done <<<"$post"

printf 'NAME: %s, AGE: %s\n' "${!myArr[@]}" "${myArr[@]}"

Here is what i get in the output:

Enter the string: name=Foo Bar&age=40
NAME: Foo Bar, AGE: 40

The input string is spitted on & using IFS environmental variable
The name and age values are parsed using parameter expansion pattern ${var##*=}
You can get all keys using ${!myArr[@]} and all values using ${!myArr[@]}

In practice, I don't think you would just make an associative array of one element. If you have multiple elements, replace the last printf line with a simple for construct to loop over the keys:

for key in "${!myArr[@]}"; do
    printf 'NAME: %s, AGE: %s\n' "$key" "${myArr["$key"]}"
done

Best Answer

Related Solutions

Ubuntu – Bash always evaluate Regex as true

Ubuntu – What’s the best way to transform a string into an associative array

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