How to parse a string into variables?

Question

I know how to parse a string into variables in the manner of this SO question, e.g.

ABCDE-123456

becomes:

var1=ABCDE
var2=123456

via, say, cut. I can do that in one script, no problem.

But I have a few dozen scripts which parse strings/arguments all in the same fashion (same arguments & variables, i.e. same parsing strategy). And sometimes I need to make a change or add a variable to the parsing mechanism.

Of course, I could go through every one of my dozens of scripts and change the parsing manually (even if just copy & paste), but that would be tedious and more error-prone to bugs/mistakes.

Is there a modular way to do parse strings/arguments as such?

I thought of writing a script which parses the string/args into variables and then exports, but the export command does not work form child-to-parent, (only vice-versa).

Answer 1

Something like this might work:

parse_it () {
    SEP=${SEP--}
    string=$1
    names=${@:2}

    IFS="$SEP" read $names <<< "$string"
}

$ parse_it ABCDE-123456 var1 var2
$ echo "$var1"
ABCDE
$ echo "$var2"
123456
$ SEP=: parse_it "foo:bar:baz" id1 id2 id3
$ echo $id2
bar

The first argument is the string to parse, the remaining arguments are names of variables that get passed to read as the variables to set. (Not quoting $names here is intentional, as we will let the shell split the string into multiple words, one per variable. Valid variable names consist of only _, letters, and numbers, so there are no worries about undesired word splitting or pathname generation by not quoting $names). The function assumes the string uses a single separator of "-", which can be overridden via the environment.

For more complex parsing, you may want to use a custom regular expression (bash 4 or later required for the -g flag to declare):

parse_it () {
    reg_ex=$1
    string=$2
    shift 2
    [[ $string =~ $reg_ex ]] || return
    i=1
    for name; do
        declare -g "$name=${BASH_REMATCH[i++]}"
    done
}

$ parse_it '(.*)-(.*):(.*)' "abc-123:xyz" id1 id2 id3
$ echo "$id2"
123

Answer 2

I think what you really want is to write your function in one script and include it in all of your other scripts. You can include other shell scripts by the source or . command.

For example, you can define your parse function in parseString.sh

function parseString {
    ...
}

And then in any of your other script, do

source parseString.sh
# now we can call parseString function
parseString abcde-12345