find piped to xargs with complex command - bash

Question

I am trying to process DVD files that are in many different locations on a disk. The thing they have in common is that they (each set of input files) are in a directory named VIDEO_TS. The output in each case will be a single file named for the parent of this directory.
I know I can get a fully qualified path to each directory with:
find /Volumes/VolumeName -type d -name "VIDEO_TS" -print0
and I can get the parent directory by piping to xargs:
find /Volumes/VolumeName -type d -name "VIDEO_TS" -print0 | xargs -0 -I{} dirname {}
and I also know that I can get the parent directory name on its own by appending:
| xargs -o I{} basename {}
What I can't figure out is how do I then pass these parameters to, e.g. HandBrakeCLI:
./HandBrakeCLI -i /path/to/filename/VIDEO_TS -o /path/to/convertedfiles/filename.m4v
I have read here about expansion capability of the shell and suspect that's going to help here (not using dirname or basename for a start), but the more I read the more confused I am getting!

Answer 1

You don't actually need xargs for this at all: You can read a NUL-delimited stream into a shell loop, and run the commands you want directly from there.
#!/bin/bash
source_dir=/Volumes/VolumeName
dest_dir=/Volumes/OtherName
while IFS= read -r -d '' dir; do
name=${dir%/VIDEO_TS} # trim /VIDEO_TS off the end of dir, assign to name
name=${name##*/} # remove everything before last remaining / from name
./HandBrakeCLI -i "$dir" -o "$dest_dir/$name.m4v"
done < <(find "$source_dir" -type d -name "VIDEO_TS" -print0)
See the article Using Find on Greg's wiki, or BashFAQ #001 for general information on processing input streams in bash, or BashFAQ #24 to understand the value of using process substitution (the <(...) construct here) rather than piping from find into the loop.
Also, find contains an -exec action which can be used as follows:
source_dir=/Volumes/VolumeName
dest_dir=/Volumes/OtherName
export dest_dir # export allows use by subprocesses!
find "$source_dir" -type d -name "VIDEO_TS" -exec bash -c '
for dir; do
name=${dir%/VIDEO_TS}
name=${name##*/}
./HandBrakeCLI -i "$dir" -o "$dest_dir/$name.m4v"
done
' _ {} +
This passes the found directory names directly on the argument list to the shell invoked with bash -c. Since the default object for for loop to iterate over is "$#", the argument list, this implicitly iterates over directories found by find.

Answer 2

If I understand what you are trying to do, the simplest solution would be to create a little wrapper which takes a path and invokes your CLI:
File: CLIWrapper
#!/bin/bash
for dir in "$#"; do
./HandBrakeCLI -i "${dir%/*}" -o "/path/to/convertedfiles/${dir##*/}.m4v"
done
Edit: I think I misunderstood the question. It's possible that the above script should read:
./HandBrakeCLI -i "$dir" -o "/path/to/convertedfiles/${dir##*/}.m4v"
or perhaps something slightly different. But the theory is valid. :)
Then you can invoke that script using the -exec option to find. The script loops over its arguments, making it possible for find to send multiple arguments to a single invocation using the + terminator:
find /Volumes/VolumeName -type d -name "VIDEO_TS" -exec ./CLIWrapper {} +