Helper to offset timezone of files in OSX.

modify_time.sh

#!/bin/bash
# Helper to modify a file modification date in case timezone is wrong.
# I noticed that when moving files from my camera whilst travelling the time zone was off and needed to bulk adjust them.
# Written and tested on osx bash, in GNU this script is superfluous since touch can do a relative -d '-2 hours' flag which osx shell doesn't support..

set -euo pipefail

SCRIPT_NAME=`basename "$0"`

# helper to log to stderr
function log() {
  >&2 echo "${1}"
}

if [[ "$#" -ne 2 ]]; then
  log "Invalid arguments."
  log "Usage: ${SCRIPT_NAME} <offset hours> <filename>"
  log "Example: ${SCRIPT_NAME} -2 P5012.jpg"
  exit 1
fi

MODIFY_HOURS=$1
MODIFY_FILE=$2

FILE_EPOCH_TIME=`stat -f "%Sm" -t %s ${MODIFY_FILE}`
MODIFIED_TIME=`date -v "${MODIFY_HOURS}H" -j -f %s ${FILE_EPOCH_TIME} "+%y%m%d%H%M"`

touch -mt ${MODIFIED_TIME} "${MODIFY_FILE}"

log "done."