My own functions in shell

Published

Thu, 8 of May, 2025

Modified

Thu, 8 of May, 2025

Reference

Great (paid) LinkedIn course by Kevin Skoglund “Unix essential training”

Fundamentals

CLI commands

  • Ctrl + C = Cancel/stop the current command (SIGINT)
  • Ctrl + Z = Pause current command (suspend, SIGTSTP)
    • fg Resume the last paused command
  • Ctrl + a = start of the command
  • Ctrl + e = end of the command
  • q = close dialogue
  • Ctrl + L → clears the terminal screen (but not history)

Shell functions’ syntax

  • $ = In shell scripting is used to reference or access a variable’s value
  • :- = sets default value if empty
  • # = Anchors the pattern to the beginning of the string (like ^ in regex).
  • %.* = Removes the shortest match of the pattern from the end (gz) of the string (archive.tar.gz –> archive.tar)
  • %%.* = Removes the longest match of the pattern from the end (tar.gz) of the string (archive.tar.gz –> archive)
  • chmod -x ... = Make the script executable (it is only needed once, unless you change the script)

My shell preferences

I use Z shell (zsh) as my default shell (check it by running the command echo $SHELL in the terminal –> /bin/zsh.

I also use the Oh My Zsh framework to manage my zsh configuration (plugin and theme setup). Basically, this “enhances” the zsh shell with a lot of features and plugins.

When you install Oh My Zsh, it creates a configuration file called ~/.zshrc in your home directory. This file is where you can customize your zsh shell environment.

  • In my ~/.zshrc file (which is similar to to how ~/.bashrc works for Bash). Here, I have set up:
    • my environment variables,
    • aliases,
    • functions, and
    • other configurations.

My own functions

I can also create my own functions in shell. Then I save them in a shell file in ~/scripts, and then can source them adding an alias in my ~/.zshrc file (i.e. make reusable functions that can be called in terminal).

Opening & modifying ~/.zshrc file

# Open/change  the file in nano editor
nano ~/.zshrc
# change | Ctrl + X | Y | Enter

# open 
open ~/.zshrc #then save 

# Reload your configuration file
source ~/.zshrc

Looking into ~/scripts dir

# List all files in the directory
ls ~/scripts
# List all files in the directory with details
ls -l ~/scripts
# List all files in the directory with details and hidden files
ls -la ~/scripts
# List all files in the directory with details and hidden files and human readable sizes
ls -lah ~/scripts

For example

# List all files in the directory | with .sh extension | with details and human readable sizes 
ls -lh ~/scripts/*.sh  
        #-rwxr-xr-x@ 1 luisamimmi  staff   1.5K May  8 00:12 /Users/luisamimmi/scripts/compress_pdf.sh
        #-rwxr-xr-x@ 1 luisamimmi  staff   1.6K May  8 00:36 /Users/luisamimmi/scripts/compress_pdf_interactive.sh
        #-rwxr-xr-x@ 1 luisamimmi  staff   3.7K May  8 11:52 /Users/luisamimmi/scripts/compress_pdf_interactive_choice.sh
        #-rwxr-xr-x@ 1 luisamimmi  staff   1.7K May  5 16:21 /Users/luisamimmi/scripts/look4files.sh
        #-rwxr-xr-x@ 1 luisamimmi  staff   1.8K May  8 00:02 /Users/luisamimmi/scripts/look4files_interactive.sh
# How is the file look4files.sh?
cat ~/scripts/look4files.sh
type ~/scripts/look4files.sh

1) look4files.sh

  • This function will look for a specific <string> in files with extensions <(PDF, docx, doc, md, R, qmd)> in <given path>
    • If a <given path> is not provided, it will look in the current working directory.
# Run by executing the script
look4files.sh "search_string" /path/to/directory

# ... or just 
look4files.sh "search_string" # in ./

The script can be downloaded here: ⬇️ look4files.sh

2) look4files_interactive.sh

Better yet, this one will prompt from the CLI for the search string and the path to search in.

# It is enough to write this in the terminal!
~/scripts/look4files_interactive.sh
# ... or (since I created an ALIAS for it in my .zshrc file)
look4

The script can be downloaded here: ⬇️ look4

3) compress_pdf_interactive_choice.sh

Similar to the previous one, but this one will compress PDF files in a given directory.

  • it provides 2 options for the level of compression:
    • standard
    • aggressive
# It is enough to write this in the terminal!
~/scripts/compress_pdf_interactive_choice.sh
# ... or (since I created an ALIAS for it in my .zshrc file)
shrinkPDF

The script can be downloaded here: ⬇️ shrinkPDF