Storing array as Environment variable to noninteractive shell with xargs

Question

This is in continuation of Storing array as Environment variable to non-interactive shell - Unix & Linux Stack Exchange. Kusalananda, asked me to ask another question.

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I want to find all markdown files that contain a particular regex match, and then sort the output with the files (that contain the most search term) in increasing order.

GREP(){
export Regex
xargs -0 -I "{}" bash -c 'grep "${GrepOption[@]}" --only-matching --with-filename --extended-regexp --regexp="${Regex}" "${1}" 2> /dev/null | wc -l | xargs printf "${1}:%s\n" ' _ "{}" \;
}
find . -name "*.md" -print0 | GREP | grep -v ':0$' | sort -n -r -k2 -t:

The user inputs "${Regex}". Here GrepOptions are array of options that depends on the user input. For example GrepOptions can be GrepOptions=("--ignore-case") or it can be some other array of grep options.

But I am unable to have the array GrepOptions be available in the subshell environment.

Any suggestions?

Answer 1

The issue is that you want to use GrepOptions, an array, as an environment variable in your code. You can't do that since arrays can't be exported.

Instead, you will have to pass the options in to you bash -c script along with the pathname that you want to run grep on.

Below, I've taken it a bit further and also pass the regular expression, and more than a single found pathname, and I'm doing this from -exec in find rather than with xargs.

I'm using -- in the call of the bash -c script to delimit the user options from the pathnames.

find . -name '*.md' -type f -exec bash -c '
    re=$1; shift
    while [[ $1 != "--" ]]; do
        opts+=( "$1" )
        shift
    done; shift
for pathname do
    printf "%s:" "$pathname"
    grep -o -E -e "$re" "${opts[@]}" -- "$pathname" |
    wc -l | tr -d "[:blank:]"
done | grep -v ":0$"' bash "$user_regex" "${user_options[@]}" -- {} + |

sort -t : -k2,2n

This find all regular files with a filename suffix of .md in the current directory or below. For batches of such files, a bash script is executed which takes a user-supplied extended regular expression ($user_regex), some user-supplied options for the grep command ($user_options, an array), along with the batch of pathnames.

The in-line script picks out the regular expression and the user options and then proceeds to loop over the found files, running grep on each and counting the number of lines that are returned.

The pathname of each file is outputted with this number at the end, after a : character.

Output indicating no matches are weeded out and the overall result is sorted.

Due to the way pathnames are being treated by this code, it will not support pathnames containing newlines or colons. The user_options array also can't contain a lone double dash.

Answer 2

bash -c 'grep ${grepOptions+$grepOptions}  ....'

• grepOptions is a shell variable housing the options to grep, space separated.
• naking use of ${var+alternative} ; in case options are nonnull then use them else an e empty unquoted is used which dissolves in parsing
• It is impled that shell variables are exportable.