Tag: bash

Retrieve “last modified” timestamp of web resource in UTC seconds

This command line assumes that “${url}” is the URL of the web resource:

curl -s -I "${url}" | grep 'Last-Modified:' | cut -c 16- | date -f - +'%s'

It can be useful to check the freshness of a download URL before a GET request.

You could compare the result to the last-modified timestamp of a local file and only download the remote file if it is newer than the existing local one.

Human readable timestamp for filenames

I use this bash alias (should work in Linux, Cygwin, probably MacOS, maybe other Unixes):

alias timestamp="date --rfc-3339=ns | tr ' '  '_'"

Then use it like this for example to archive a file:

mv somefile somefile_$(timestamp)

You should see something like

`somefile' -> `somefile_2014-11-13_11:45:46.980175800-04:00'

If you don’t like colons in file names, change tr ' ' to tr ' :'.