This is the fourth part of my Effective Shell series, a set of practical examples of ways to be more efficient with everyday tasks in the shell or at the command line.
- Part 1: Navigating the Command Line
- Part 2: Become a Clipboard Gymnast
- Part 3: Getting Help
- Part 4: Moving Around
- Part 5: Interlude - Understanding the Shell
- Part 6: Everything You Don’t Need to Know About Job Control
- Part 7: The Subtleties of Shell Commands
In this article we’ll look at the key elements of navigation in the shell.
Getting Comfortable Moving Around
You might already spend a lot of time in the shell, running various command line programs or using tooling for development projects or operational tasks. But you might also still switch back to a more visual paradigm for working with files, directories and resources.
Being able to perform everyday file and folder manipulation tasks directly from the shell can really speed up your workflow. Let’s look at some common tasks and see how we can work with them in the shell. Along the way we’ll also introduce some of the most frequently used tools and commands to work with the filesystem.
Where Am I?
The first command to become familiar with is pwd (‘print working directory’). This command will echo the current absolute path. You can also use the $PWD environment variable:
$ pwd
/Users/dave/repos/github/dwmkerr/effective-shell
$ echo $PWD
/Users/dave/repos/github/dwmkerr/effective-shell
Depending on your shell, or your command-line setup (which we will discuss in a later chapter), you might also see your working directly on the command-line.
Changing Directory
Most likely one of the most familiar commands out there, the cd or chdir function changes the current directory:
$ pwd
/Users/dave/repos/github/dwmkerr/effective-shell
$ cd
$ pwd
/users/dave
$ cd -
~/repos/github/dwmkerr/effective-shell
$ pwd
/Users/dave/repos/github/dwmkerr/effective-shell
$ cd ~
$ pwd
/users/dave
Here we can see that running cd with no parameters moves to the users ‘home’ directory. This directory is always available in the $HOME environment variable.
Running cd - will switch back to the previous directory — this is very useful if you want to quickly jump somewhere and then back again.
You can use ~ as an alias for the home directory, allowing you to quickly move to personal folders, with commands such as cd ~/Downloads.
Most commonly, you will specify a path when changing directory. This can be a fully qualified path, or it can be a relative path:
$ cd /dev
$ cd ~/repos
$ cd ./github
You can use the special link .., which is a folder that points to the parent directory to move ‘upwards’:
$ pwd
/Users/dave/repos/github/dwmkerr/effective-shell
$ cd ../../
$ pwd
/Users/dave/repos/github
Exploring a Directory
Once we are in a directory, we will often want to see the contents. The ls (“list directory contents”) command is useful here:
$ pwd
/Users/dave/repos/github/dwmkerr/effective-shell
$ ls
1-navigating-the-command-line LICENSE
2-clipboard-gymnastics README.md
3-getting-help sed.1
4-moving-around
By default, the ls command will list the files and directories. We can show more information with the -l (“long format”) flag:
$ ls -l
total 48
drwxr-xr-x 6 dave staff 192 Mar 5 16:01 1-navigating-the-command-line
drwxr-xr-x 5 dave staff 160 Oct 10 2017 2-clipboard-gymnastics
drwxr-xr-x 4 dave staff 128 Dec 19 2017 3-getting-help
drwxr-xr-x 3 dave staff 96 Mar 7 15:39 4-moving-around
-rw-r--r-- 1 dave staff 1066 Jun 10 2017 LICENSE
-rw-r--r-- 1 dave staff 561 Mar 7 15:30 README.md
-rw-r--r-- 1 dave staff 15707 Mar 5 16:01 sed.1
Now we can see the permissions, the link count (which is rarely particularly useful and varies from platform to platform), the owner, the group, the size and the modification date (as well as the name).
We can make the sizes more human readable, and sort by size with a few more flags -h (“human readable”) and -s (“sort by size”):
$ ls -lhS
total 48
-rw-r--r-- 1 dave staff 15K Mar 5 16:01 sed.1
-rw-r--r-- 1 dave staff 1.0K Jun 10 2017 LICENSE
-rw-r--r-- 1 dave staff 561B Mar 7 15:30 README.md
drwxr-xr-x 6 dave staff 192B Mar 5 16:01 1-navigating-the-command-line
drwxr-xr-x 5 dave staff 160B Oct 10 2017 2-clipboard-gymnastics
drwxr-xr-x 4 dave staff 128B Dec 19 2017 3-getting-help
drwxr-xr-x 3 dave staff 96B Mar 7 15:39 4-moving-around
There are lot of options for ls. Check the chapter Getting Help for some tips on how to get more information on a command!
Managing the Directory Stack
You might find that you want to move to a number of directories, then return to where you started. This can be particularly useful when scripting. You can use the pushd (“push onto directory stack”) and popd (“pop from directory stack”) commands to add or remove directories from the stack:
$ pwd
/Users/dave/repos/github/dwmkerr/effective-shell
# OK - I'm writing my article at the moment, but want to check my downloads, and come back shortly...
# Move to the downloads folder...
$ ls
aws-nuke-v2.8.0-darwin-amd64
# OK cool - the tool I was downloading has arrived, let's use it...
cd aws-nuke-v2.8.0-darwin-amd64
./aws-nuke
# Now I want to go back to my article...
$ popd
~/Downloads ~/repos/github/dwmkerr/effective-shell
~/Downloads
$ popd
~/repos/github/dwmkerr/effective-shell
In this case, using cd - would not be sufficient — that would just switch us from the aws-nuke folder to Downloads and back again. But by using the directory stack we can save where we are, move, and then ‘pop’ our way back to where we started.
Auto-Completion
Pressing tab when using commands like cd will generally show an auto-completion menu:
$ cd ~/repos/ # press 'tab' now...
github/ gitlab/ local/ scratch/
Pressing tab again will cycle through options, and shift-tab will cycle backwards. Enter will select an option, escape (or Ctrl-C) will cancel.
Some shells, such as zsh, support even more advanced auto-completion. For example, we can auto-complete to fill in partially specified directory names:
% cd ~/r/g/d/e # press tab now...
% cd ~/repos/github/dwmkerr/effective-
effective-container-engineering/ effective-shell/
Auto-completion is generally very shell specific. We’ll look more into the different shells that are available in later chapters. But in general, if you are uncertain, pressing tab will often show a sensible set of options.
That’s It!
This is a small chapter, but an important one. Later on, as we start to do more file and system manipulation from the shell, moving and copying files and so on, we will build on these concepts. But it is critical to first know the basics of how to move around the filesystem with the shell.