[SOLVED] Collapsing a Bash array into a comma-separated string

Turbocapitalist · 05-18-2019, 10:34 PM

I'm looking to find Bash-only way to efficiently concatenate all positional parameters passed to a shell function. They should all end up in a single string but separated by commas. What I came up with first was this:

Code:

tb ()
{
    local files=$(realpath $@);
    local att=$(echo $files | tr ' ' ',');
    echo foo "a='$att'"
}

So if I write

Code:

pwd
tb a
tb b c d

I would get

Code:

/home/me
foo a='/home/me/a'
foo a='/home/me/b,/home/me/c,/home/me/d'

However, that will choke on file names and paths containing spaces. I see several other ways, but they all seem to leave a trailing comma and that would break things. Or they require calling sed or other programs.

How should I really merge $1, $2, $3, ..., $n into a single, comma-separated string using just bash?

ondoho · 05-19-2019, 01:31 AM

I will take your thread title: Collapsing a Bash array into a comma-separated string literally:

Code:

array=( ... ) # assuming this is filled already
string=""
for i in "${array[@]}" # this exact syntax will preserve array elements even if they have spaces in them
do
    string="$i,$string"
done
# we have a superfluous trailing comma now, remove it:
string="${string%,}"

(not tested)

astrogeek · 05-19-2019, 02:13 AM

Here is a simple loop that should do it, assuming arr is your already set array:

Code:

for i in "${arr[@]}"; do 
    str="${str}${c}${i}" 
    c=',' 
done

ondoho · 05-19-2019, 02:21 AM

^ code golf!
works for a standalone bash script; uninitialised variables default to the empty string.

Turbocapitalist · 05-19-2019, 03:03 AM

Ok. Thanks, both.

I'll go with this one for the time being:

Code:

tb() {  local c i str;
        for i in "${@}"; do
                i=$(realpath $i);
                str="${str}${c}${i}"
                c=','
        done;
        echo str=$str; }

It seems there are problems reading from realpath even with the --zero option. As an example, the following also chokes on file names and paths with spaces:

Code:

tx() {  local c i str;
        while read -r -d '' i; do
                str="${str}${c}${i}"
                c=','
        done < <(realpath --zero ${@});
        echo str=$str; }

astrogeek · 05-19-2019, 03:19 AM

Quote:

Originally Posted by Turbocapitalist

It seems there are problems reading from realpath even with the --zero option. As an example, the following also chokes on file names and paths with spaces:

Try quoting the argument to realpath...

Code:

tb() {  local c i str;
        for i in "${@}"; do
                i=$(realpath "$i");
                str="${str}${c}${i}"
                c=','
        done;
        echo str=$str; }

Or...

Code:

tx() {  local c i str;
        while read -r -d '' i; do
                str="${str}${c}${i}"
                c=','
        done < <(realpath --zero "${@}");
        echo str=$str; }

Turbocapitalist · 05-19-2019, 03:22 AM

Quote:

Originally Posted by astrogeek

Try quoting the argument to realpath...

Thanks. I had tried just about everything except that. It was the original input that was off. GIGO.

astrogeek · 05-19-2019, 03:26 AM

We all do it!

You are welcome!

syg00 · 05-19-2019, 05:17 AM

I always found bash "interesting" with quotes - a PITA actually. Not worth the grief - if another tool does it easier/better I'll use that.
But I do admire the persistence of others, and the solutions you all come up with.

pan64 · 05-19-2019, 05:27 AM

I would suggest you to use shellcheck, it will definitely help you to solve this issue.

Turbocapitalist · 05-19-2019, 05:32 AM

Quote:

Originally Posted by syg00

I always found bash "interesting" with quotes - a PITA actually. Not worth the grief - if another tool does it easier/better I'll use that.
But I do admire the persistence of others, and the solutions you all come up with.

I'm not keen on bash much either but it is the default shell for many distros and a few other operating systems.

The actual problem I am trying to solve is a work-around for Thunderbird's inability to accept relative paths for attachments submitted via the shell. So I have made a shell function to first calculate the full absolute path of each attachment and then submit all that to Thunderbird in such a way that they are attached to a new message.

I'm open for suggestions on other ways to solve that.

As for shells, I've tended to stay with defaults but have been experimented more and more with zsh on my GNU/Linux systems and am contemplating eventual migration.

grail · 05-19-2019, 06:01 AM

I know this one has been solved, but I cam to the party late, so how about:

Code:

#!/usr/bin/env bash

tb()
{
	local -a files

	mapfile -t files <<<"$(realpath "$@")"

	IFS=","
	echo "foo a='${files[*]}'"
}

tb "$@"

syg00 · 05-19-2019, 06:04 AM

C'mon grail - "pure bash".
coreutils is GNU, but it ain't bash.

grail · 05-19-2019, 08:17 AM

Quote:

Originally Posted by syg00

C'mon grail - "pure bash".
coreutils is GNU, but it ain't bash.

Hey, I didn't bring in realpath ... that was from OP ... so the rest is "pure bash" .... otherwise adding any path would be a non-issue

NevemTeve · 05-20-2019, 02:29 AM

Using printf:

Code:

array=(1 "2 2" '3 3')
Tmp=$(printf "%s," "${array[@]}")
echo ${Tmp%,}