Convert many images to any ImageMagick-supported format in parallel

convertto

#!/bin/bash
# intended for use with https://github.com/erichs/composure
# requires ImageMagick's 'convert' and GNU Parallel
# source: https://gist.github.com/ernstki/495ff1a60509e0b771f0d65740de1a19/edit

convertto () 
{ 
    author 'Kevin Ernst'
    about 'Convert arguments to another image format based on extension'
    example "$ convertto jpg *.heic"
    example "$ convertto -geometry 200x200 png *.heic"
    param "-* - any valid ImageMagick 'convert' command line option"
    param '$* - image(s) to convert'
    group 'graphics'
    group 'util'

    local endopts dryrun ext opts=() files=()
    local -A formats
    local cache=~/.cache/imagemagick_formats.lst
    local now=$(date +%s)
    local setx=$(builtin set +o | grep '\bxtrace\b')

    # set TRACE=1 in the environment for execution tracing (for debugging)
    # you can also just run this inside a subshell with 'func() ()'
    # instead of 'func() {}', and not worry about setting 'set +x' when
    # you're done, but I wanted to see if this was possible to do (it is)
    (( TRACE )) && set -x
    trap "$setx" RETURN

    # cache ImageMagick's list of formats at most once per day; also not
    # stricly necessary -- it doesn't take *that* long to run, but I wanted
    # to figure out how to do it
    if [[ ! -s $cache ]] || (( (now - $(date -r $cache +%s)) > 86400 )); then
        mkdir -p ~/.cache
        identify -list format \
          | awk '/^ *[A-Z0-9*]+ /{gsub(/\*/,"",$1);if($1){print $1}}' \
          > $cache
    fi

    # read in list of formats
    while read fmt; do formats[$fmt]=1; done < $cache

    while (( $# )); do
        if (( endopts )); then
            files+=("$1"); shift; continue
        fi
        case $1 in
            -h|--help)
                reference $FUNCNAME
                return
                ;;
            -n|--dry-run)
                dryrun=1
                ;;
            --)
                endopts=1
                ;;
            -*)
                opts+=("$1")
                ;;
            *)
                if [[ -r $1 ]]; then
                    files+=("$1")
                elif [[ ${opts[@]: -1} =~ ^- && ! $ext ]]; then
                    # probably an argument to a previous ImageMagick option
                    opts+=("$1")
                # the output of `identify -list format` is upper-case, so
                # upper-case the argument and see if it's a key in $formats
                elif [[ ${formats[${1^^}]} && ! $ext ]]; then
                    ext=$1
                else
                    echo "ERROR: Unexpected option or unsupported image format '$1'." >&2
                    return 1
                fi
                ;;
        esac
        shift
    done

    if [[ ${#files[@]} -eq 0 ]]; then
        echo  "ERROR: No files specified for conversion." >&2
        return 1
    fi
        
    parallel ${dryrun:+--dry-run }convert ${opts:+"${opts[@]}"} {} {.}.$ext ::: "${files[@]}"
}