Add some specific time while using the linux command “date”

Question

In linux, date can help me to print the current time. If want to print the current time + 1 hour, what option should I give?

Answer 1

Linux and macOS in a single command

If you need to write scripts that work on both Linux servers and macOS workstations, you can silence the error of the first date call and 'OR' it (||) with the other. It doesn't matter which comes first.

date -u -d "+${max_age}Seconds" +"%Y-%m-%dT%H:%M:%SZ" 2>/dev/null || \
date -u -v "+${max_age}S"       +"%Y-%m-%dT%H:%M:%SZ"

For example, this bash function uploads a file to AWS S3 and sets a Expires: and Cache-Control: headers.

s3_upload_cache_control(){
  local max_age_seconds="${1}" ;shift         # required
  local bucket_path="${1}"     ;shift         # required
  local filename="${1}"        ;shift         # required
  local remote_filename="/${1:-${filename}}"  # optional
  local fmt="+%Y-%m-%dT%H:%M:%SZ"
  aws s3 cp                                                          \
    "${filename}"                                                    \
    "s3://${bucket_path}${remote_filename}"                          \
    --expires                                                  "$(   \
      date -u -d "+${max_age_seconds}Seconds" $fmt 2>/dev/null  ||   \
      date -u -v "+${max_age_seconds}S"       $fmt               )"  \
    --cache-control max-age=$max_age,public                          \
    --acl public-read
}