Bash functional

Fancy loops that let you process things incrementally in a pipeline.
You'll almost never use these directly, but it might be inspiration for a more useful function.

Filter

# filters out results not matching 'grep foo'
find . \
  | while read line; do \
    echo $line | grep foo && echo "$line"; \
  done

Map

NOTE:

If your callable accepts parameter as stdin, you don't need map (ex. grep/sed work just fine from stdin).

map() {
    # Call callable/params($*), passing each each STDIN line as the last parameter
    local input

    while read -r input; do
        "$@" "${input}"
    done
}

Example

print_if_divisible_by_2() {
    if [ $(($1 % 2)) -eq 0 ] ; then
        echo "$1:yes"
    else
        echo "$1:no"
    fi
}

echo {1..4} | tr ' ' '\n' | map print_if_divisible_by_2
#> 1:no
#> 2:yes
#> 3:no
#> 4:yes

Reduce

TODO:

wip, but this is general idea

reduce() {
    # callable/params must accept aggregate as 2nd-last param, and input as last param.
    #
    # EXAMPLE:
    #   sum() { echo $(($1 + $2)) }
    #   echo {1..10} | tr ' ' '\n' | reduce sum 0
    local callable="${@:1:$#-1}"
    local aggregate="${@[$#-1]}"
    local input

    while read -r input; do
        aggregate="$("${callable[@]}" "${aggregate}" "${input}")"
    done
    echo "${aggregate}"
}