Bash read array from an external file

Question

I have setup a Bash menu script that also requires user input. These inputs are wrote (appended to) a text file named var.txt like so:

input[0]=\'192.0.0.1\'         


        

Answer 1

You can encapsulate your variable extraction in a function and take advantage of the fact that declare creates local variables when used inside a function. This technique reads the file each time the function is called.

readvar () {
    # call like this: readvar filename variable
    while read -r line
    do
        # you could do some validation here
        declare "$line"
    done < "$1"
    echo ${!2}
}

Given a file called "data" containing:

input[0]='192.0.0.1'
input[1]='username'
input[2]='example.com'
input[3]='/home/newuser'
foo=bar
bar=baz

You could do:

$ a=$(readvar data input[1])
$ echo "$a"
username
$ readvar data foo
bar

This will read an array and rename it:

readarray () {
    # call like this: readarray filename arrayname newname
    # newname may be omitted and will default to the existing name
    while read -r line
    do
        declare "$line"
    done < "$1"
    local d=$(declare -p $2)
    echo ${d/#declare -a $2/declare -a ${3:-$2}};
}

Examples:

$ eval $(readarray data input output)
$ echo ${output[2]}
example.com
$ echo ${output[0]}
192.0.0.1
$ eval $(readarray data input)
$ echo ${input[3]}
/home/newuser

Doing it this way, you would only need to make one call to the function and the entire array would be available instead of having to make individual queries.