Listing all variables in a file in bash

Question

When writing bash scripts I like to write self contained functions which take an argument and perform operations based on that/those argument(s) rather than have global variables being declared in several different places in the code decreasing readability.

The issue arises when you have a function which needs to make use of several variables. Passing something like 10 variables to a function is just plain ugly and for that a simple associative array can be used.

If we want to declare those variables on an external file, the "source" command allows you to import them all in.

The issue then becomes, how do I list the variables declared ONLY inside this file so I can build my associative array with them? I have been able to use a combination of "compgen" and a loop to build associative arrays out of a list of variables but how does one list only the variables found inside the file, regardless of what they are called, so I can loop through them and build my array?

Answer 1

You could do an egrep for some variable declaring syntax on your file and then get the variable name by cutting it, for example like this:

egrep '[a-zA-Z0-9"'\''\[\]]*=' /path/to/file |egrep -v '^#' |cut -d'=' -f1 |awk '{print $1}'

---

If you had a file with content like this

#!/bin/bash

A="test"

somerandomfunction () {
        echo "test function"
        B="test"
}

#C="test"

DEF="test"
GHI1="test"
JKL[1]="test"
JKL['a']="test"
JKL["b"]="test"

the output of the above command would look like this:

A
B
DEF
GHI1
JKL[1]
JKL['a']
JKL["b"]

---

Explanation of the commands:

1. The first egrep searches for lines containing any number and combination of lowercase (a-z) and/or uppercase (A-Z) letters and/or square brackets (\[\]) and/or single ('\'') and/or double (") quotation marks followed by a =.
2. The second egrep excludes lines beginning with a # since those are usually interpreted as comments and would not generate or set a variable.
3. The cut command cuts away everything from the = to the line ending.
4. The awk command prints the first occurence of something else than spaces or tabs and therefore effectively cuts away empty space in front of variable names.

---

The output of the command could be used in a loop or something like this:

for VAR in $(egrep '[a-zA-Z0-9"'\''\[\]]*=' /path/to/file |egrep -v '^#' |cut -d'=' -f1 |awk '{print $1}'); do
  eval echo "\$${VAR}"
done