Bash utility to output a range of bytes from a stream

byte_range.sh

#!/bin/bash

# byte_range $start $end
#   - Outputs the bytes between the starting and ending values from the stdin stream
#
#     - $start - Starting byte to display
#     - $end   - Ending byte to display

isInteger() {
  local regex_numeric='^[0-9]+$'
  [[ "$1" =~ $regex_numeric ]]
}

byteRange() {
  local start="$1"
  local length="$2"

  tail -c +"$start" | head -c "$length"
}

checkInputs() {
  local start="$1"
  local end="$2"

  if ! isInteger "$start" || ! isInteger "$end"; then
    echo "Non-integer provided as input. Exiting"
    exit 1
  fi

  if [ $start -ge $end ]; then
    echo "Starting value must be less than ending value"
    exit 1
  fi
}

diff() { 
  echo "$1 - $2" | bc
}

checkInputs "$1" "$2"

START="$1"; END="$2"; LENGTH=$(diff "$END" "$START");

cat - | byteRange "$START" "$LENGTH"