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Commands

tldr man pages: https://tldr.sh

List of POSIX commands: https://en.wikipedia.org/wiki/List_of_POSIX_commands

The Art of Command Line: https://github.com/jlevy/the-art-of-command-line

Shell One-liners: https://github.com/trimstray/the-book-of-secret-knowledge#shell-one-liners-toc

Introduction to the Command Line - https://shop.fsf.org/books-docs/introduction-command-line (can be downloaded as PDF)

Oh-heck, a terminal command for when you forget other terminal commands - https://news.ycombinator.com/item?id=30720834 - https://oh-heck.dev

Advanced macOS Command-Line Tools: https://saurabhs.org/advanced-macos-commands

Use the GNU tools instead fo the macOS: https://ryanparman.com/posts/2019/using-gnu-command-line-tools-in-macos-instead-of-freebsd-tools/

Notes​

zsh is the default shell in macOS since Catalina (10.15, released October 2019) - see https://support.apple.com/kb/HT208050

Command history is saved in ~/.zsh_history.

Terminal shortcuts​

  • Ctrl + R: Recall
    • Ctrl + R again to see next match
    • Return to execute
    • Ctrl + G to exit without executing
    • Esc to exit but leaving searched command
  • Ctrl + Z: send to the background

& to run in the background​

From https://manpages.org/bash

If a command is terminated by the control operator &, the shell executes the command in the background in a subshell. The shell does not wait for the command to finish, and the return status is 0.

https://unix.stackexchange.com/questions/86247/what-does-ampersand-mean-at-the-end-of-a-shell-script-line

nohup to continue running when you close the shell​

https://en.wikipedia.org/wiki/Nohup

Means "no hang up".

Is usually combined with &, like this: nohup command &. Together, you can use it to run a web server indefinitely, for example.

Heredoc​

Multiline strings without \n.

https://linuxize.com/post/bash-heredoc/

Tips​

  • !!: run the previous command
  • What shell is used: echo $SHELL

Command-line pro tips: https://twitter.com/addyosmani/status/1264854298799665152

Use curly braces in the command-line to quickly create multiple related files with less typing source:

touch index.{js,css} # creates index.js and index.css
touch {P,H1,H2}.tsx # creates P.tsx, H1.tsx and H2.tsx

You can also use this with npm: https://twitter.com/nucliweb/status/1096327937308135425

Environment variables​

List all environment variables: printenv or env. See What is the difference between 'env' and 'printenv'?. You can also print a specific envar: printenv ANDROID_HOME. In Linux you can print many (eg printenv ANDROID_HOME PATH) but this does not work in macOS (it only prints the first one).

# set environment variable
export TF_VAR_vpc_cidr_block="10.0.0.0/16"

# unset environment variable
unset NODE_ENV

What is the difference between env, setenv, export and when to use?

What is the difference between set, env, declare and export when setting a variable in a Linux shell?

Command substitution​

https://www.gnu.org/software/bash/manual/html_node/Command-Substitution.html

AWS_ACCOUNT_ID=$(aws sts get-caller-identity --query Account --output text)

Run the same command multiple times​

https://stackoverflow.com/questions/3737740/is-there-a-better-way-to-run-a-command-n-times-in-bash

From https://developer.hashicorp.com/terraform/tutorials/aws/aws-asg#scale-instances:

for i in `seq 1 5`; do curl https://www.google.com; echo;  done

Aliases​

On your .zshrc or .bash_profile put:

alias l='ls -la'

cd​

cd # Go to user's home (~). You can also do 'cd ~'
cd - # Go to the previous directory
cd / # Go to the root directory
cd ~username # Go to the user's root directory

cp​

cp -r dir1 dir2 # Recursively

mv​

mv file.txt dir

rm​

rm -r dir # Recursive is required to delete a directory
rm -r * # Remove all files in current directory, except hidden files
rm -r * .* # Remove all files in current directory, including hidden files

mkdir / rmdir​

mkdir -p dir1/dir2/dir3 # With -p if dir1 and dir2 don't exist, it creates them
rmdir -p dir1/dir2/dir3 # With -p it removes dir1 and dir2 too

touch​

Either updates the access or modification date of a file, or creates an empty file if it doesn't exist.

Useful to create locks, eg to avoid multiple editing or access. See https://unix.stackexchange.com/questions/109003/what-are-the-legitimate-uses-of-the-touch-command

echo​

echo "Java home is $JAVA_HOME"
echo "something" >> file.txt # Appends
echo "something" > file.txt # OVERWRITES ALL FILE CONTENT
echo -n "abc" # Do not add a newline (at the end)

cat​

Backup some file before modifying it, just in case:

cat file.txt > file-backup.txt # Equivalent to 'cp file.txt file-backup.txt'

Use cat /proc/cpuinfo to display CPU information on a EC2 instance.

less​

If the file is big is better use less not cat.

less file.txt

Use /Whatever for searching.

find​

find . -type d -name "build"

find . -type d -name "build" -exec rm -rf {} +

find . -type f -name "*.iml"

find . -type f -name "*.iml" -exec rm -rf {} +

Exclude: find . -type d -name "dist" | grep -v 'node_modules'

See user-friendly alternative fd - https://github.com/sharkdp/fd

diff​

diff -qr Dir1 Dir2

# Exclude directories
diff -qr Dir1 Dir2 --exclude=.git --exclude=node_modules

tree​

tree somefolder

To ignore something (eg a folder) use -I <wild-card-pattern>. Eg tree -I node_modules or tree -I venv. There can be multiple -I options.

fc​

fc [-e ename] [-lnr] [first] [last]

fc -s [pat=rep] [command]

https://www.geeksforgeeks.org/fc-command-linux-examples

List recent commands in history: fc -l

lsof​

If we are running a server at (eg) port 3000 we can do lsof -i :3000 and it will print information about the process that started the server. Doing lsof -t -i :5000 gives the process id. Hence, to kill the process you can do kill -9 $(lsof -t -i :3000).

free​

Prints information about the machine's memory. You can use it on a EC2 instance.

free -m

Output:

              total        used        free      shared  buff/cache   available
Mem:           3856        1024        2012          64         819         2549
Swap:          2047           0        2047

See What is available memory while using free command?, What is available and free memory in response of free command on Linux? and https://www.linuxatemyram.com.

at​

To schedule tasks in the future.

echo "command_to_be_run" | at 09:00
echo "command_to_be_run" | at now + 10 minutes

Example: terminate EC2 instance at N minutes: https://github.com/AWSinAction/code3/blob/e8131b2a740d22cd5d487aa30d242336421c496e/chapter05/ec2-iam-role.yaml#L111

sed​

On macOS, don't bother to try to use the built-in sed, since you get the error 'sed: 1: "eas.json": invalid command code e' all the time. Use GNU sed instead, as advised here. Install it with brew install gnu-sed. Then use gsed instead of sed, or alias it with alias sed='gsed', or add it to the path with PATH="/opt/homebrew/opt/gnu-sed/libexec/gnubin:$PATH".

https://www.gnu.org/software/sed

Manual: https://www.gnu.org/software/sed/manual/sed.html

Replace value in file:

sed -i "s/THE_VALUE/some_value/" file.txt
sed -i "s/THE_VALUE/$SOME_VAR/" file.txt

s means substitute. See The s Command for more options.

Another example. If we have:

const a = {
  version: '0.0.1',
}

We can do:

sed -i "s|version: '.*'|version: '$VERSION'|" file.ts

sed: -e expression #1, char 19: unknown option to `s'​

Beware that if the interpolated value contains a / (eg a URL or a path) it will fail with:

sed: -e expression #1, char 19: unknown option to `s'

See:

Since you can use any delimiter, to fix it do for example:

sed -i "s|THE_VALUE|$SOME_VAR|" file.txt