curltail.bats

#!/usr/bin/env bats
#
# Bash Automated Testing System (BATS)
# https://github.com/sstephenson/bats
#
# Test curltail, both sourced and executed

@test "Missing argument, sourced" {
  . curltail.sh
  run curltail
  [ "$status" -eq 2 ]
  [ "$output" = "curltail requires a URL" ]
}

@test "Missing argument, executed" {
  run ./curltail.sh
  [ "$status" -eq 2 ]
  [ "$output" = "curltail requires a URL" ]
}

@test "Sourcing curltail" {
  . curltail.sh
  run curltail http://www.google.com >/dev/null
  [ "$status" -eq 1 ]
}

@test "Executing curltail" {
  run ./curltail.sh http://www.google.com >/dev/null
  [ "$status" -eq 0 ]
}

curltail.sh

#!/bin/bash
#
# Use curl to tail a file over HTTP, kind of.
#
# Uses range requests (RFC 7233) to get the last N bytes of a resource. 
# Change `chunk` below if you want to get more or fewer byte.
# Note that many HTTP 1.1 servers do not support range GET requests, 
# so you'll end up with the whole file, after all. *sad trombone*

curltail()
{
  local chunk=500 # bytes
  url=$1 && [ "$url" ] || {
    >&2 echo "${FUNCNAME[0]} requires a URL"
    return 1
  }
  curl -v -X GET -H "range: byte=-$chunk" "$url"
}

# run the function, if we are not being sourced
if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
  curltail "${1}"
fi