#!/usr/bin/env bash
set -o errexit -o nounset -o pipefail
IFS=$'\n\t\v'
cd `dirname "${BASH_SOURCE[0]:-$0}"`

#functions
function cleanup() {
  rm -rf junk
}
function fail() {
  >&2 echo $1  # echo the first arg to stderr
  exit ${2:-1} # exit $2 or exit 1
}
cleanup

# variables & default values
X=${1:-"default"} # X=$1, or "default" if $1 not set
Y=${2:-}          # Y=$2, or nothing (use to bypass nounset)

# test for empty variable
# this is equivalent to `test -z "$Y"`
# so you can get help with `man test`
if [[ -z "$Y" ]]; then
  echo "Y not set"
fi

# retrieve exit code from individual pipe sections
# '!' bypasses pipefail
! echo "my command" | grep "whatever"
if [[ ${PIPESTATUS[1]} -ne 0 ]]; then
  echo "grep failed" >&2 # echo to stderr
  >&2 echo "grep failed" # works too
fi

# start & stop a background process
sleep 10s &
PID=$! # PID of last started background process
! ps -p $PID &> /dev/null # this will fail if background process failed to start
if [[ ${PIPESTATUS[0]} -ne 0 ]]; then
  fail "no background process to kill" 1
else
  kill $PID
fi

# ask for input
DEFAULT_Z="Z"
read -p "Type a Z (default ${DEFAULT_Z}): " MY_Z
MY_Z=${MY_Z:-${DEFAULT_Z}}

# search and replace in one or more files
FILELIST=$'a.sh\tb.sh'
! sed -i -- "s|my search|${MY_Z}|g" ${FILELIST} &>/dev/null # ignore both stdout and stderr