defines a function `assign` that allows returning multiple values from a function/command

bash-multiassign.sh

#!/bin/bash

# assign var1 varN... = c arg...
# execute c and assign captured values to the list of variables
#
# values can be output from c by redirecting/writing to:
#    >${outvar[x]}
#    >&x
# where x is the index of the variable you want to return the value
# in
assign() {
    local tdir=$( mktemp -d )
    local resetnullglob
    shopt -u | grep -q nullglob && resetnullglob=1 && shopt -s nullglob
    trap 'rm -rf "$tdir"' RETURN
    local -a outvar
    local ret redirs c=1
    while [[ $# -gt 0 && $1 != = ]]; do
        > "${tdir}/${1}"
        outvar[$c]="${tdir}/${1}"
        redirs="$redirs ${c}>${tdir}/${1}"
        shift
        c=$(( c + 1 ))
    done
    shift
    if [[ $# -ne 0 ]]; then
        eval "$@" $redirs
        ret=$?
        local varfile varname resetnullglob
        for varfile in $tdir/* ; do
            varname=${varfile##*/}
            eval "${varname}"'=$(<$varfile)'
        done
    fi
    [[ $resetnullglob ]] && shopt -u nullglob
    return $ret
}

# modstrings_and_fortune
# invoke with `assign`
# in $@:
#    $1: <string to uppercase>
#    $2: <string to lowercase>
#    $3: <string to remove numbers from>
# out:
#    1: <uppercased string>
#    2: <lowercased string>
#    3: <string without numbers>
#    4: <a fortune>
modstrings_and_fortune() {
    local inarg1=${1}
    local inarg2=${2}
    local inarg3=${3}

    echo "${inarg1}" | tr a-z A-Z > ${outvar[1]}
    echo "${inarg2}" | tr A-Z a-z > ${outvar[2]}
    echo "${inarg3}" | tr -d 0-9 > ${outvar[3]}
    fortune > ${outvar[4]} 2>&1
    return 27
}

main() {
    local var1 var2 var3 myfortune
    local stdout stderr

    assign var1 var2 var3 myfortune = modstrings_and_fortune uppercaseme LOWERCASEME no23423432numbers
    echo "ret=$?"
    echo "var1=$var1"
    echo "var2=$var2"
    echo "var3=$var3"
    echo "fortune=$myfortune"

    echo

    # there are readable and unreadable directories in /var/log
    # find will produce output on both stdout and stderr in that case
    assign stdout stderr = find /var/log
    echo "filecount=$( wc -l <<<"$stdout" )"
    echo "errorlines=$( wc -l <<<"$stderr" )"
}

main