Shell Tips — Commands & Bash Scripting

The terminal is one of the most powerful tools in a developer’s toolkit. Whether you’re on Linux, macOS, or WSL on Windows, mastering a handful of Shell commands and understanding how to write Bash scripts can dramatically speed up your workflow.

Essential Commands

ls — List Directory Contents

ls shows what’s in the current directory. The flags make it genuinely useful:

ls          # basic list
ls -l       # long format: permissions, owner, size, date
ls -a       # show hidden files (starting with .)
ls -la      # combine both: long format + hidden files

The -la combo is the one you’ll use 95% of the time. It gives you the full picture of a directory including dotfiles like .zshrc, .gitignore, etc.

cd — Change Directory

cd /path/to/dir   # absolute path
cd Documents      # relative path
cd ..             # go up one level
cd ~              # go to home directory
cd -              # go back to previous directory

cd - is underrated — it toggles between the last two directories you visited, great when you’re jumping between two project folders.

cp — Copy Files or Directories

cp file.txt backup.txt          # copy a file
cp -r folder/ backup_folder/    # copy a directory recursively
cp *.png ~/Pictures/            # copy all .png files to Pictures

Always use -r (recursive) when copying directories, otherwise cp will refuse.

mv — Move or Rename

mv old_name.txt new_name.txt    # rename a file
mv file.txt ~/Documents/        # move a file
mv folder/ ../other_folder/     # move a directory

mv does double duty: moving and renaming are the same operation. There’s no dedicated rename command in Shell.

chmod — Change File Permissions

Permissions control who can read, write, or execute a file. They apply to three groups: owner, group, and others.

chmod +x script.sh      # make a file executable
chmod 755 script.sh     # rwxr-xr-x (owner full, others read+execute)
chmod 644 file.txt      # rw-r--r-- (owner read+write, others read only)

There is also a symbolic mode using +, -, and = to add, remove, or set permissions, and u (user/owner), g (group), o (others), a (all) to target who:

chmod +x script.sh      # give execute to everyone
chmod -x script.sh      # remove execute from everyone
chmod +r file.txt       # give read to everyone
chmod -w file.txt       # remove write from everyone

chmod u+x script.sh     # give execute to owner only
chmod g-w file.txt      # remove write from group
chmod o-r file.txt      # remove read from others
chmod a+r file.txt      # give read to all (same as +r)

chmod u+rwx,go+rx file  # owner full, group and others read+execute
chmod o= file.txt       # remove all permissions from others

The numeric mode (755, 644) is the most common in practice. Each digit is a sum of three base values:

Add them together to combine permissions:

alias — Create Command Shortcuts

alias lets you define a shortcut for any command or chain of commands:

alias ll="ls -la"
alias gs="git status"
alias ..="cd .."
alias ...="cd ../.."

The problem: aliases defined in the terminal only last for the current session.

Making Aliases Permanent with .zshrc

To persist aliases across sessions, add them to your shell config file. For Zsh (default on macOS and most modern Linux distros), that’s ~/.zshrc:

# Open .zshrc with your editor
nano ~/.zshrc

# Add your aliases at the bottom
alias ll="ls -la"
alias gs="git status"
alias gp="git push"
alias ..="cd .."

# Reload the config without restarting the terminal
source ~/.zshrc

For Bash users the file is ~/.bashrc instead.

Writing a Bash Script

A Bash script is a plain text file containing a sequence of Shell commands. The first line — the shebang — tells the OS which interpreter to use.

The Shebang Line

#!/bin/bash

This must be the very first line of the file. It points to the Bash binary, so the script runs with Bash regardless of what shell the user has active.

A Practical Example

Here’s a script that creates a timestamped backup of a directory:

#!/bin/bash

SOURCE="$HOME/Projects"
DEST="$HOME/Backups"
TIMESTAMP=$(date +"%Y-%m-%d_%H-%M")
BACKUP_NAME="backup_$TIMESTAMP"

mkdir -p "$DEST/$BACKUP_NAME"
cp -r "$SOURCE/" "$DEST/$BACKUP_NAME/"

echo "Backup created: $DEST/$BACKUP_NAME"

Save it as backup.sh, then make it executable and run it:

chmod +x backup.sh
./backup.sh

Key Script Concepts

Variables — no spaces around =:

NAME="Sam"
echo "Hello, $NAME"

Conditionals:

if [ -f "file.txt" ]; then
  echo "File exists"
else
  echo "File not found"
fi

Loops:

for file in *.txt; do
  echo "Processing $file"
done

Functions:

greet() {
  echo "Hello, $1"
}
greet "Sam"

Quick Reference