Not Yet Another Another Guide About Bash

Despite the growing adoption of tools and orchestrators like Kubernetes, Flux, and Dagger, shell commands and Bash scripts remain an integral part of a software engineer’s daily workflow.

“The total amount of Bash in the universe remains constant” — collective wisdom

I would dare say that any “trick” that can improve the general speed or knowledge regarding this matter is highly valuable. Without further ado, I will share a compilation of different commands which has helped me greatly.

• Quickly change the directory to the user's home directory (specified by $HOME environment variable), equivalent to running cd ~ :

# cd without any arguments takes you to your home directory
cd

• Go Back to the Previous Directory: Going back to the previous directory (based on $OLDPWDinternal variable) — is especially useful when navigating through long paths:

cd -

• Execute the last command: useful for rerunning the previous command

!!

• Check the return code of the last command: useful when checking various return codes (in Unix and Linux, every command returns a numeric code between 0–255):

echo $?

• Globbing “searching for files using wildcard expansion” — list files that start with the lettera:

# * matches any sequence of characters
ls a*

Or sometimes maybe you don’t have ls available:

command not found

# expand and print all the files and directories in the current directory
echo .* *

• Create a nested directory structure:

mkdir -p provisioning/{datasources,notifiers,dashboards/backup}

# will create
.
└── provisioning
    ├── dashboards
    │   └── backup
    ├── datasources
    └── notifier

• Get the Process ID of this shell itself — SHELL is not always defined by the bash shell:

# echo $SHELL
ps -p $(echo $$)

• Emulating tree command — on minimal distros, tree command may not exist, therefore the following alias provides the much-needed recursive directory listing:

alias tr3='function tr3(){ find ${1:-.} | sed -e "s/[^-][^\/]*\//  |/g" -e "s/|\([^ ]\)/|-\1/"; unset -f tr3;}; tr3'

tr3

• Heredoc for file creation — here document is a special-purpose code block. It uses a form of I/O redirection to feed a command list to an interactive program or a command.

Heredoc that prints the evaluated values directly to the terminal ( or even create/override a file i.e. text by cat<<EOF>text by redirecting the output to a file).

heredoc

SHEBANG