Code for parsing a key/value in in file from shell script

Question

I have a file that I need to look up a value by key using a shell script. The file looks like:

HereIsAKey This is the value

How can I do so

Answer 1

if HereIsAKey is unique in your file, try this with grep:

myVar=$(grep -Po "(?<=^HereIsAKey ).*" file)

Answer 2

If you only need one variable at a time, you can do something like this:

#!/bin/bash
cat file | while read key value; do
  echo $key
  echo $value
done

The problem with this solution: The variables are only valid inside the loop. So don't try to do $key=$value and use it after the loop.

Update: Another way is I/O redirection:

exec 3<file
while read -u3 key value; do
  eval "$key='$value'"
done
exec 3<&-
echo "$keyInFile1"
echo "$anotherKey"

Answer 3

If you don't have a grep that supports Perl-compatible regular expressions, the following seems to work:

VAR=$(grep "^$KEY " file | cut -d' ' -f2-)

Answer 4

If the file is unsorted, lookups will be slow:

my_var=$( awk '/^HereIsAKey/ { $1=""; print $0; exit}' value-file )

If the file is sorted, you can get a faster lookup with

my_var=$( look HereIsAkey value-file | cut -d ' ' -f 2- )

Answer 5

get () {
    while read -r key value; do
        if [ "$key" = "$1" ]; then
            echo "$value"
            return 0
        fi
    done
    return 1
}

The two return statements aren't strictly necessary, but provide nice exit codes to indicate success or failure at finding the given key. They can also help distinguish between "the key has a empty string for the value" and "the key was not found".

Answer 6

I use a property file that is shared across multiple languages, I use a pair of functions:

load_properties() {
    local aline= var= value=
    for file in config.properties; do
        [ -f $file ] || continue
        while read aline; do
            aline=${aline//\#*/}
            [[ -z $aline ]] && continue
            read var value <<<$aline
            [[ -z $var ]] && continue
            eval __property_$var=\"$value\"
            # You can remove the next line if you don't need them exported to subshells
            export __property_$var
        done <$file
    done
}

get_prop() {
    local var=$1 key=$2
    eval $var=\"\$__property_$key\"
}

load_properties reads from the config.properties file populating a set of variables __property_... for each line in the file, get_prop then allows the setting of a variable based on loaded properties. It works for most of the cases that are needed.

Yes, I do realize there's an eval in there, which makes it unsafe for user input, but it works for what I needed it to do.