Parallelize s3 copy / move actions by using screens and forked processes (usage: `./s3-parallel <from> <to> <number_of_screens_to_use>`)

s3-parallel

#!/bin/bash

action=${1:?Please specify whether to mv or cp.}
from=${2:?Specify the full s3 path to move or copy from.}
to=${3:?Specify the full s3 path to move or copy to.}
number_of_screens=${4:-10}

case $action in
  mv)
    echo "Going to MOVE data from '$from' to '$to'."
    ;;

  cp)
    echo "Going to COPY data from '$from' to '$to'."
    ;;
  *)
    echo "Unknown action $action. Specify whether to mv or cp."
    exit 1
    ;;
esac

# Ensure s3 paths ends with a slash
function fix_path() {
    path_to_fix="$1"
    case "$path_to_fix" in 
        */) 
        ;;
        *)
            path_to_fix="$path_to_fix/"
        ;;
    esac

    echo $path_to_fix
}

# Set the date command, macOS depends on coreutils (brew install coreutils)
if [[ "$OSTYPE" == "darwin"* ]]; then
    # macOS
    date_command="gdate"
else
    date_command="date"
fi

from=$(fix_path "$from")
to=$(fix_path "$to")

files_to_copy=$(aws s3 ls --recursive "$from" | awk '{print $4}')
number_of_files=$(echo "$files_to_copy" | wc -l | sed 's/ //g')
files_per_screen=$((($number_of_files + $number_of_screens - 1) / $number_of_screens))

index=0
files_in_batch=0
screen_batch_index=0
screen_batch_name_prefix="s3-parallel-$action-"

for file in $files_to_copy; do
    old_file_path="${from}${file}"
    new_file_path="${to}${file}"

    files_in_batch=$(($files_in_batch+1))
    commands="${commands} aws s3 $action \"$old_file_path\" \"$new_file_path\"; "

    index=$(($index+1))
    if [[ ("$(($index % $files_per_screen))" -eq 0) || ($index -eq $number_of_files) ]]; then
        current_epoch=$(eval "$date_command +%s%N")
        screen_name="${screen_batch_name_prefix}${screen_batch_index}-${current_epoch}"
        echo "Starting new screen '$screen_name' with $files_in_batch item(s) to $action."
        screen -S "$screen_name" -d -m bash -c "eval \"$commands\" wait"

        commands=""
        screen_batch_index=$(($screen_batch_index+1))
        files_in_batch=0
    fi
done