Using Docker to run CLI utilities with access to local files

Docker local CLI examples

#!/usr/bin/env bash

# This works only if all files specified as arguments below the PWD.
docker run --rm -it -v ${PWD}:${PWD} -w ${PWD} \
    jrottenberg/ffmpeg:4.3-alpine -i input.mp4 -c copy output.mkv

# If you need input directories that aren't below your current PWD,
# you can mount a parent directory of the input files (preferably read-only
# with the narrowest possible scope) to an identical location in the
# container, and then reference those files absolutely.
docker run --rm -it -v /mnt:/mnt:ro -v ${PWD}:${PWD} -w ${PWD} \
    jrottenberg/ffmpeg:4.3-alpine -i /mnt/dir1/input.mp4 -c copy output.mkv

# The standard way must be used if you want maximum specificity, but it makes
# commands less re-usable. However, it can simplify complex directory
# relationships.
docker run --rm -it \
    -v /a/b/c/d/input:/mnt/input:ro -v /x/y/output:/mnt/output -w /mnt \
    jrottenberg/ffmpeg:4.3-alpine -i input/file.mp4 -c copy output/file.mkv
    
# Some possible bash aliases to make it easier to run CLI utilities that can
# access local files.

alias run-pwd="docker run --rm -it -v ${PWD}:${PWD} -w ${PWD}"
alias run-mnt="docker run --rm -it -v /mnt:/mnt:ro -v ${PWD}:${PWD} -w ${PWD}"