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.

NOTE:

If your callable accepts parameter as stdin, you don't need map/filter (ex. sed/grep work just fine from stdin).
you could also use xargs to pass stdin lines as callable params.

Filter

# Call callable/params($*), passing each each STDIN line as the last parameter
#
# EXAMPLE:
#   divisible_by_2() { [ $(($1 % 2)) -eq 0 ] }
#   echo {1..10} | tr ' ' '\n' | filter divisible_by_2
#   #> 2
#   #> 4
#   #> ...
#
filter() {
    local input

    while read -r input; do
        if "$@" "${input}" 2>&1 > /dev/null ;
            echo "${input}"
        fi
    done
}

Map

# Call callable/params($*), passing each each STDIN line as the last parameter
#
# EXAMPLE:
#   print_divisible_by_2() { 
#     [ $(($1 % 2)) -eq 0 ] && echo "$1:yes" || echo "$1:no"
#   }
#   echo {1..10} | tr ' ' '\n' | map print_divisible_by_2
#   #> 1:no
#   #> 2:yes
#   #> ...
#
map() {
    local input

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

Reduce

# callable/params must accept aggregate as 2nd-last param, and input as last param.
#
# EXAMPLE:
#   sum() { echo $(($1 + $2)) }
#   echo {1..10} | tr ' ' '\n' | reduce sum 0
#   #> 55
#
reduce() {
    local input
    local callable="${@:1:-1}" # all until last param
    local aggregate="${@[-1]}" # last param

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