Introduction
There are situations when we need to execute the same command line instruction over and over again, it becomes worse if the command in question has arguments, furthermore if we are forced to modify the output to make it readable. Most of us end up creating some kind of cheat sheet to save all those "complex" commands, so we have them handy in case we need to run it again.
We can save ourselves time and effort using an "alias command" to stop typing or copying the same command again and again, aliases makes possible to execute a command or set of commands by using a pre-defined "string" that we can customize the way we want.
Creating Aliases
We have a couple of options when creating aliases:
- Temporary
- Permanent
Temporary aliases are created in the current terminal session, that means that if we close this session or we open a new open those aliases will not be available.
Permanent aliases in the other hand are persistent no matter if the current terminal session is ended or even if the host machine is rebooted. The aliases information has to be written and saved into the user’s shell configuration profile file. In my case I'm using macOS so all the aliases changes has to be saved in the~/.bash_profile, if you are a Linux user you should save the aliases in the~/.bashrc.
For both Linux and MacOS, these user’s shell configuration profile files are typically located in the $HOME directory.
Aliases in Action
Imagine I want to list all the files within a directory, including the creation date and owner. In Windows command prompt we get this file information this running the "dir" command, but unfortunately the is is not known bash command in Linux \ Unix systems, if you try to run "dir" it will return an error message like this:
[dba mastery] $ dir-bash: dir: command not found
The solution is to create an alias for the "dir" command, using "ls -ltr" we will be able to display the file information the way we want (files by creation date and owner), so let's create an alias for that:
alias dir = "ls -ltr"
As you can see it is very simple, we have to run the command "alias" followed by a short name in this case "dir" followed by the "=" sign, then finally we provide the command line instruction "ls -ltr" that will execute as the command when calling the alias "dir".
This is what happens when the "dir" alias is called:
[dba mastery] $ dirtotal 8-rw-r--r-- 1 dba staff 976 Sep 8 2018 README.mddrwxr-xr-x 6 dba staff 192 Oct 8 2018 Directory_1drwxr-xr-x 21 dba staff 672 Nov 26 13:11 Directory_2drwxr-xr-x 5 dba staff 160 Jan 26 13:11 Directory_3drwxr-xr-x 22 dba staff 704 Feb 26 13:18 Directory_4drwxr-xr-x 5 dba staff 160 Mar 24 03:06 Directory_5
It is time to focus on Docker now, let's create some aliases using the previous example.
Creating Aliases for Common Docker Commands
Now that you know the basics of aliases, let's create some for the most common Docker commands. First thing first, we have to navigate to our user home directory (cd $HOME). Once we are at this location simply edit the .bash_profile or .bashrc file using the editor of your choice, in my case I will use "vim" as follows:
[dba mastery] $ cd $HOME[dba mastery] $ vi .bash_profile# Docker aliases (shortcuts)# List all containers by status using custom formatalias dkpsa='docker ps -a --format "table {{.Names}}\t{{.Image}}\t{{.Status}}"'# Removes a container, it requires the container name \ ID as parameteralias dkrm='docker rm -f'# Removes an image, it requires the image name \ ID as parameteralias dkrmi='docker rmi'# Lists all images by repository sorted by tag namealias dkimg='docker image ls --format "table {{.Repository}}\t{{.Tag}}\t{{.ID}}" | sort'# Lists all persistent volumesalias dkvlm='docker volume ls'# Diplays a container log, it requires the image name \ ID as parameteralias dklgs='docker logs'# Streams a container log, it requires the image name \ ID as parameteralias dklgsf='docker logs -f'# Initiates a session withing a container, it requires the image name \ ID as parameter followed by the word "bash"alias dkterm='docker exec -it'# Starts a container, it requires the image name \ ID as parameteralias dkstrt='docker start'# Stops a container, it requires the image name \ ID as parameteralias dkstp='docker stop'~:wqPlease keep in mind, you can use any name\label for the aliases. I used the "dk" prefix in all the aliases because it was convenient for me but you can use what might be easier to memory \ write for you.
It is time to check how the aliases are working, for this example I will display all the containers by status using the "dkpsa" alias:
[dba mastery] $ dkpsaNAMES IMAGE STATUS24HOP_DKR mcr.microsoft.com/mssql/server:2017-CU14-ubuntu Exited (0) 11 hours agoSQLSat830 mcr.microsoft.com/mssql/server:2017-CU13-ubuntu Exited (0) 13 hours agoSimpleTalk mcr.microsoft.com/mssql/server:2017-CU13-ubuntu Exited (0) 4 weeks agomaster_2017_CU12 microsoft/mssql-server-linux:2017-latest Exited (0) 5 months agomaster_2017_CU11 microsoft/mssql-server-linux:2017-CU11 Exited (0) 2 months agomaster_ag1 microsoft/mssql-server-linux:2017-latest Exited (255) 2 months agomaster_ag2 microsoft/mssql-server-linux:2017-latest Exited (137) 5 months ago
Other example, checking what images I have in my Docker local repository using the "dkimg" alias:
[dba mastery] $ dkimgREPOSITORY TAG IMAGE IDmcr.microsoft.com/mssql/server 2017-CU11 885d07287041mcr.microsoft.com/mssql/server 2017-CU12 4095d6d460cdmcr.microsoft.com/mssql/server 2017-CU12-ubuntu 4095d6d460cdmcr.microsoft.com/mssql/server 2017-CU13-ubuntu 314918ddaedfmcr.microsoft.com/mssql/server 2017-CU14-ubuntu 644ca19cb10dmcr.microsoft.com/mssql/server 2017-latest-ubuntu 314918ddaedfmcr.microsoft.com/mssql/server 2019-latest 7af596b24973microsoft/mssql-server-linux 2017-CU11 167af87c9fb5microsoft/mssql-server-linux 2017-CU12 4095d6d460cdmicrosoft/mssql-server-linux 2017-latest 4095d6d460cd
Conclusion
The creation of aliases can help you to save some time and effort when executing repetitive bash instructions, in this article we learned how Linux \ Unix aliases works, types and also an example of how to create some aliases for Docker to make our administration tasks a little bit easier.
Another good case of the use of aliases can be automation, I find easy to incorporate short commands rather in a script than a complex set of instructions; also improves the script readability in some cases.
