mkvmerge in a bash script does not execute

Question

I have made a script which does mux a videofile, multiple audiofiles and multiple subtitles into one .mkv.

the script tries to run:
"/usr/bin/mkvmerge" -o "test.mkv" "--default-track" "0:yes" "--forced-track" "0:no" "--display-dimensions" "0:853x462" "-d" "0" "-A" "-S" "-T" "(" "mux.mkv" ")" "--language" "0:eng" "--default-track" "0:yes" "--forced-track" "0:no" "--no-global-tags" "--no-chapters" "-a" "0" "-D" "-S" "-T" "(" "test_eng_1.opus" ")" "--default-track" "0:no" "--forced-track" "0:no" "--no-global-tags" "--no-chapters" "-a" "0" "-D" "-S" "-T" "(" "test_und_2.opus" ")" "--language" "0:eng" "--default-track" "0:no" "--forced-track" "0:no" "--no-global-tags" "--no-chapters" "-s" "0" "-D" "-A" "-T" "(" "test_eng_3.idx" ")" "--language" "0:fra" "--default-track" "0:no" "--forced-track" "0:no" "--no-global-tags" "--no-chapters" "-s" "0" "-D" "-A" "-T" "(" "test_fra_5.idx" ")" "--language" "0:spa" "--default-track" "0:no" "--forced-track" "0:no" "--no-global-tags" "--no-chapters" "-s" "0" "-D" "-A" "-T" "(" "test_spa_4.idx" ")" "--title" "test"

If I run the script it shows: line 214: (the stuff above): No such file or directory

If I copy and paste the output and run it in bash all runs OK:

mkvmerge v7.7.0 ('Six Voices') 64bit built on Mar  3 2015 16:43:14 ... 
Muxing took 3 seconds.

Here is the part of the script which tries to run mkvmerge:

213 mux="\"/usr/bin/mkvmerge\" -o \"$gname.mkv\" $muxvideo$muxaudio$muxsub$tacks$title"
214 "$mux"

Why does it run in the terminal but not in the script?

Answer 1

Your script defines a variable mux with its value being the big long mkvmerge command you pasted, literally with all those double quotes and everything: notice how the double quotes are backslash-escaped so that they get included literally in the string.

Then it does:

"$mux"

Which tries to run a command named after the contents of that variable, spaces and quotes and all. Since there is no command called "/usr/bin/mkvmerge" -o "test.mkv" "--default-track" etc..., you get the error.

Are you sure that line shouldn't be this?

eval "$mux"

...which would parse the contents of $mux as a shell command line, thus interpreting all those spaces and double quotes as shell syntax instead of treating it literally?

Or much more simply... just execute mkvmerge with all the right arguments without first building a quoted command and stuffing it into a variable and then executing the variable as a command.