A forking bash program to distribute input among workers

forklift

#!/bin/bash
# Copyright 2023 David Farrell

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
set -euo pipefail
declare -i num_workers=1
declare -i num_fifos=0
declare -i next_fifo=1
declare -a fifos=("") # zeroth unused

new_fifo() {
  local fn="${TMPDIR-/tmp}/forklift-$1"
  fifos[$1]="$fn"
  num_fifos=$((num_fifos+1))
  mkfifo "$fn"
  eval "tail -f '$fn' --pid $$ | ${cmd/\{\{w\}\}/$1} &"
}

cleanup() {
  for i in $(seq 1 ${num_fifos});do
    rm -f "${fifos[$i]}"
  done
}
trap cleanup EXIT

# process args
while getopts "w:" opt;do
  case "$opt" in
    'w') num_workers="$OPTARG";;
  esac
done
shift $((OPTIND-1))
if [ $# -ne 1 ]; then
  echo -e "Must provide 1 command. Usage:\n\tforklift [-w #] command"
  exit 1
fi
declare cmd="$1"

# process input
while read -r;do
  ((next_fifo > num_fifos)) && new_fifo $next_fifo
  echo "$REPLY" > "${fifos[$next_fifo]}"
  if ((next_fifo==num_workers)); then
    next_fifo=1
  else
    next_fifo=$((next_fifo+1))
  fi
done