Bash function to get the date a file is modified, works for BSD or Linux

file_modifed_date.sh

#!/bin/bash
# return unix timestamp for file or 0 if it doesn't exist
[ `uname` == "Darwin" ] && STAT_FORMAT_FLAG='-f' || STAT_FORMAT_FLAG='-c'
file_modified () {
    file=$1
    if [ -f "$file" ] && [ -n "$file" ]; then # make sure filename is non-empty, -f will return true otherwise
         echo `stat $STAT_FORMAT_FLAG "%a" $file`
    else
        echo "0";
    fi
}