DIRSTACK

I was recently poking around on my Terminal (Mac OS X) and I noticed one of the environment variables was:

DIRSTACK=()

So I checked the man page for the bash shell to see what I could find about it:

man bash

Reading the man page I find DIRSTACK is an array relating to popd, pushd and dirs. Rather than using cd to change to a directory I can use pushd. For example:

pushd ~/Downloads

This will change directory to ~/Downloads plus it will add the directory to the DIRSTACK array. I can add some more to the DIRSTACK using:

pushd ~/Documents
pushd /Volumes

Now if I issue a dirs I will see:

/Volumes ~/Documents ~/Downloads

If you search for popd, pushd and dirs on the bash man page you will find all the settings for these builtin commands:

dirs [-clpv] [+n] [-n]

+n display the nth entry from the left, e.g. +2 will display the entry in position 2, this is zero-indexed
-n displays the nth entry from the right, just like the +n this is zero-indexed, e.g. -0 is the first entry
-c clears the DIRSTACK
-l displays a longer list, e.g. ~ gets expanded to the full directory name /Users/darrell
-p display one entry per line
-v display one entry per line with a number at the start of each line

You might thing the -v option is just line numbers but they are more than that. The numbers are directly related to the -n and +n option. Additionally, I can refer to specific entries in the list using ~n. For example, if the dirs -v displays:

 0  ~/Public
 1  ~/Downloads
 2  ~/Documents
 3  ~

then ls -l ~2 will be the same as ls -l ~/Documents. I can also use the tilde notation for popping elements off the stack as well. The next command, popd, has the following format:

popd [-n] [+n] [-n]

-n is literally -n, when you normally popd it will change to the directory you pop, -n will suppress this

+n removes n entries from the left, e.g. +2 will remove from third element from left (zero-indexed)

-n removes n entries from the right, e.g. -1 will pick the second element from right

The pushd commands looks similar:

pushd [-n] [dir]
pushd [-n] [+n] [-n]

-n is literally -n, and like popd it adds to the stack but does not cd to the new directory.

[dir] will push [dir] on the DIRSTACK then cd [dir]

+n will rotate the stack so the nth directory from the left is at the top

-n will roate the stack so the nth directory from the right is at the top

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Interactive Ruby Shell

My current project uses Ruby and has a web testing component to it. The obvious choice for testing a web application with Ruby would be Selenium-WebDriver.

If you are familiar with Ruby you should be familiar with the Interactive Ruby Shell or irb.

If I enter irb at a command prompt I am placed at the Interactive Ruby Shell:

1.9.3-p547 :001 > 

Once you are at the Interactive Ruby Shell you can try things to see how they work. In a compiled language like Java you would have to compile the code into class files then execute them. With Ruby you can actually type the lines out and see what happens immediately. For example, to do the basic Selenium example I can enter:

require 'selenium-webdriver'
driver = Selenium::WebDriver.for :chrome

At this point a chrome browser should open. If it does not possible problems might be if chromedriver isn't in your PATH. Before you open the command prompt make sure that chromedriver is in your PATH. If it is in the PATH and you run irb then the Ruby code above should open a Chrome browser. It also assumes you have Chrome installed.

Once the browser opens you can do:

driver.methods - Object.methods

All objects in Ruby have a methods method. All objects also inherit Object. So the line above says to give me all the methods for driver and subtract all the Object methods from the list. So what will remain are the Selenium WebDriver methods:

 => [:save_screenshot, :screenshot_as, :action, :mouse, :keyboard, :navigate, :switch_to, :manage, :get, :current_url, :title, :page_source, :quit, :close, :window_handles, :window_handle, :execute_script, :execute_async_script, :first, :all, :script, :[], :browser, :capabilities, :ref, :find_element, :find_elements]

From this list I can see all the things I can do with driver, an instance of Selenium WebDriver. So now that I have an instance of WebDriver and I have the browser open I can enter:

driver.get 'http://www.google.com'
text_field = driver.find_element :id => 'gbqfq'
text_field.send_keys 'Selenium'
puts driver.title
driver.quit

As I type these lines I will see the browser switch to http://www.google.com, sending the text 'Selenium' to the browser and the browser closing (driver.quit).