Curl Dump Response Headers to STDOUT and Ignore Response Body

Goals

Return only HTTP response header when opening a web page using curl. This is useful when we are interested in processing response headers only.

Command

We will utilize /dev/stdout and /dev/null to achieve what we want.

$ curl https://notes.rioastamal.net -D /dev/stdout -o /dev/null --silent
HTTP/2 200
date: Sun, 06 May 2018 23:42:37 GMT
content-type: text/html; charset=UTF-8
set-cookie: __cfduid=d6347d57f364b276150034b241b19cdb01525650157; expires=Mon, 06-May-19 23:42:37 GMT; path=/; domain=.rioastamal.net; HttpOnly
expires: Sun, 06 May 2018 23:42:37 GMT
cache-control: private, max-age=0
last-modified: Sun, 06 May 2018 23:42:05 GMT
x-content-type-options: nosniff
x-xss-protection: 1; mode=block
expect-ct: max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
server: cloudflare
cf-ray: 416f4deb6f51a320-HKG

Reference

• https://unix.stackexchange.com/questions/16357/usage-of-dash-in-place-of-a-filename

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How to Extract Specific Directory from Tarball

Problem

We have huge file of gzipped tarball and we want to extract only specific directory from the tarball.

Solution

Make sure the pattern we want to extract by searching it first. As an example we want to extract directory named johndoe-website, but we did not know the full pattern of the directory.

$ tar tvf the-archive.tar.gz | grep johndoe-website
home/sites/clients/johndoe-website/javascripts/main.js
home/sites/clients/johndoe-website/styles/main.css
home/sites/clients/johndoe-website/index.html

From the output above we knew that the pattern of the directory is home/sites/clients/johndoe-website. Command below will extract johndoe-website from the archive and strip the 3 leading directories.

$ tar xvf the-archive.tar.gz --strip-components=3 -C /destination/path home/sites/clients/johndoe-website

Command above works in GNU Tar and BSD Tar (Mac OS X).

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Expose Port Inside Running Container on Docker Toolbox for Mac

Problem

Docker only allows to define port that need to be exposed when doing container creation. When the container already running and new port need to be exposed, you're out of luck.

Goal

You want to expose new port which run by application inside a running container, so you can hit the docker-vm-ip:port to access the port on Mac OS X.

Assumptions

• IP of Boot2Docker VM (Which run by Virtualbox) is 192.168.99.100
• IP of the docker container running the application is 172.17.0.2
• The application listen on address 0.0.0.0 and port 80

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