Following on from theDocker knowledge to get you through the day, andGit commands to get you through the day posts, this will cover Shell commands. Once again, it aims to get you through the day.

First of all, it's worth noting that there are many shells: bash, sh, zsh etc. For a comprehensive list of shells, and their comparison, head over toWikipedia.

Basic commands

Let's cover off some basics that will hopefully get you on your way.

man is the manual application. Use this to find information about all the other commands, and options. e.g.man ls will give you the manual page for thels command.

For extra points, you can define an environment variable that changes how you view the manual. e.g.

MANPAGER=catmanls

This will output the entire manual to the screen, without any interaction. MyMANPAGER is set toless -X. With your new knowledge of theman command, find out what-X means forless.

ls lists files in a given directory.ls -lGh is a favourite of mine which lists all the files in the current directory, enables colourised output, and provides human readable file sizes! There are many options tols, so I recommend you read the output fromman ls and find what output suits your needs.

Whilst we are talking about listing files, I always like to remind folks aboutgit ls-files which lists all the files in a git repo. Sorry to slip in agit command there.

df anddu are two disk related commands that I use quite often.

df displays information about free disk space. I recommend running it withdf -h so the output is a little more human readable.

du comes in really handy when you want summary information about folder/file sizes. The-d flag allows you to define the depth of the summary. For example to find the total size of yournode_modules folder:

❯du-d 0-h node_modules198M  node_modules

If you want to know the size of all the packages, individually, innode_modules, then you can run

❯du-d 1-h node_modules 16K  node_modules/write 12K  node_modules/callsites 16K  node_modules/is-extendable ...

vim,less,tail, andcat allow you to view file content. Each of these commands take a file as a parameter.vim is too big to cover here, so try runningvimtutor to see if that helps you learn vim.

tail is handy when coupled with the-f flag, to "follow" the output of a file, e.g. a log filetail -f /path/to/file.

cat simply outputs all the content to the terminal, with no paging.

less allows you to page through content withctrl+f andcrtl+b.

The following commands help with process management:ps,kill,pgrep,top orhtop.

ps aux will output all the processes, for any user, running on the machine. You can drop thex if you want to get processes running for any user with a controlling terminal, i.e. you ran the command from a terminal. Another way to get process information ispgrep which takes a command parameter. For example we can runpgrep -l vim which will output the process IDs (PID) of all runningvim commands.

The output fromps andpgrep then can be used to stop a proces. For examplekill [pid] will kill the process with the same[pid].

top, and the more functional sister commandhtop, will show you statistical information about running commands. This covers memory, CPU, how long it's been running etc.

Understanding where things are installed is really handy, and there are a few commands that can help.

which will explain where the command you pass in as a parameter is being run. Sowhich go will show you the version of go being used when you rungo.

where will show you all the versions of the command you pass in. So I have two versions of bash right now.

❯ where bash/opt/homebrew/bin/bash/bin/bash❯ which bash/opt/homebrew/bin/bash

So I have two versions ofbash, but the one I would use is thehomebrew version, as shown by the output ofwhich.

type helps explain what kind of "thing" the command is. Some examples are shown below.

❯typebashbash is /opt/homebrew/bin/bash❯typeenvgenvg is analiasforenv |grep-i❯typedhagendhagen is a shellfunctionfrom /Users/ben/.oh-my-zsh/custom/docker.zsh

The order of precedence for determining which commands to run, is defined by the$PATH environment variable. Runecho $PATH to understand the ordering, with the first path taking priority.

sed is really useful for automating changes to files/content.

date |sed"s| |-|g"Sun-28-Mar-2021-21:22:58-BST

This takes the output ofdate (an arbitrary example) and replaces spaces for hyphens.

Remember the time when you ran that command, but cannot quite remember it? Wellhistory has your back. By running this command, it will output all the commands you have ran previously.

Two tips:

• Add a space before running a command, and it won't be stored in your history file. Handy if you are entering a password, for example.
• ctrl+r will reverse look up your history.

Some little tidbits I find useful:

• echo $? will get you the exit code of the last command executed.
• !$ will get the last parameter of the previous command.
• !! will get the entire last command, sosudo !! runs the previous command assudo.
• {1..5} represents numbers 1 to 5. So we can runfor x in {1..5}; do echo $x; done.

Pipes

Pipes allow you to chain commands together. It allows you to take the output from one command andpipe it into the next command.

env | sort will sort all your environment variables, so it's easier to find what you're looking for. You could even create this as analias.

history | grep [command] will find a command in your history (commands you have run before).

These are just arbitrary examples, but you can keep chaining commands together, to deliver the output you want.

Environment variables

Environment variables help you configure your system and applications. You can set them in the following way:

export MY_ENV_VAR=boo It's customary to capitalise the name of the environment, but it's not mandatory. To remove an environment variable you can rununset MY_ENV_VAR.

You can set environment variables to be loaded when you start your shell/terminal, if you add theexport statements to something like~/.bashrc,~/.bash_profile,~/.zshrc etc.

Aliases

Aliases are great. They can be used to provide a shorter command so you are more efficient. A great community project for aliases, isoh-my-zsh.

Just like environment variables, we can set, unset, and store them in a config file.

alias week='date +%V' will get you the week number if you runweek. To get rid of this alias, you can rununalias week.

I hope this provides some useful knowledge to get you through your day in the terminal.

See also

• Docker knowledge to get you through the day
• Git commands to get you through the day
• 101 Bash Commands and Tips for Beginners to Experts
• ohmyzsh - "A delightful community-driven (with 1800+ contributors) framework for managing your zsh configuration."
• fzf - A command line fuzzy finder. You can hook this intocrtl-r which I highly recommend.