Extract all variable values in a shell script

Question

I'm debugging an old shell script; I want to check the values of all the variables used, it's a huge ugly script with approx more than 140 variables used. Is there anyway I can extract the variable names from the script and put them in a convenient pattern like:

#!/bin/sh
if [ ${BLAH} ....
.....
rm -rf ${JUNK}.....

to

echo ${BLAH}
echo ${JUNK}
...

Answer 1

Try running your script as follows:

bash -x ./script.bash

Or enable the setting in the script:

set -x

Answer 2

You can dump all interested variables in one command using:

set | grep -w -e BLAH -e JUNK

To dump all the variables to stdout use:

set

or

env

from inside your script.

Answer 3

In bash, but not sh, compgen -v will list the names of all variables assigned (compare this to set, which has a great deal of output other than variable names, and thus needs to be parsed).

Thus, if you change the top of the script to #!/bin/bash, you will be able to use compgen -v to generate that list.

That said, the person who advised you use set -x did well. Consider this extension on that:

PS4=':$BASH_SOURCE:$LINENO+'; set -x

This will print the source file and line number before every command (or variable assignment) which is executed, so you will have a log not only of which variables are set, but just where in the source each one was assigned. This makes tracking down where each variable is set far easier.

Answer 4

You can extract a (sub)list of the variables declared in your script using grep:

grep -Po "([a-z][a-zA-Z0-9_]+)(?==\")" ./script.bash | sort -u

Disclaimer: why "sublist"?

The expression given will match string followed by an egal sign (=) and a double quote ("). So if you don't use syntax such as myvar="my-value" it won't work. But you got the idea.

grep Options

• -P --perl-regexp: Interpret PATTERN as a Perl regular expression (PCRE, see below) (experimental) ;
• -o --only-matching: Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line.

Pattern

I'm using a positive lookahead: (?==\") to require an egal sign followed by a double quote.