Day 2 - Shell Fundamentals (Bash)

This lesson covers the shell skills used every day: how commands are built, how quoting changes meaning, how PATH finds programs, and how to get help quickly. Examples assume the Bash shell.

Prerequisites

• A Linux system from Day 1 in a VM, in WSL, or on bare metal
• Access to a terminal window
• Ability to update packages with sudo apt update on Ubuntu or sudo dnf upgrade on Fedora

Anatomy of a command

Commands usually have four parts.

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program  -s  --long  argument1  argument2

• program: the tool to run, for example ls or cat
• options: short options start with a single dash, long options start with two dashes
• arguments: items the program works on, such as files or directories

Examples:

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ls -la               # list files with details, show hidden files
mkdir projects && cd projects
cp /etc/hosts ./hosts.backup

Built-in and external commands

Some commands are Bash built-ins. Others are external programs stored on disk. Use type or command -V to check.

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type cd        # builtin
command -V ls  # usually /usr/bin/ls
which ls       # path of an external program

Built-ins provide help with help <name>.

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help cd
help alias

External programs provide manuals and inline help.

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man ls
ls --help | less

Quoting rules that matter

Quoting changes how Bash parses text.

• Unquoted text allows globbing and word splitting; spaces break words; wildcards expand
• Single quotes '...' keep text exact; nothing inside changes
• Double quotes "..." allow variable expansion and command substitution while protecting spaces
• Backslash \ escapes the next character only

Examples:

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# unquoted: splits on spaces and expands globs
printf %s\n *

# single quotes: literal text
printf '%s\n' *

# double quotes: expands variables but keeps spaces
name="Majd Banat"
echo "Hello $name"

# escape one character
echo A\ B

Command substitution

Use $(...) to insert the output of one command into another.

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# show kernel version inside a sentence
echo "Kernel: $(uname -r)"

# save the current date in a variable
now=$(date +%F)
echo "Today is $now"

# nested example
echo "User $(id -un) on host $(hostname)"

Avoid backticks `...` because they are hard to nest and read.

Globbing and expansions

Bash expands patterns before running the program.

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# wildcards
ls *.log
ls file?.txt

# character classes
ls report_[AB].pdf

# brace expansion creates many words quickly
mkdir -p logs/{nginx,app,db}
cp -v config.{example,backup}

# tilde expansion to the home directory
cd ~

To search for a literal asterisk or question mark, quote the pattern.

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grep "*.log" notes.txt

PATH and how Bash finds programs

When a program name is typed, Bash searches the directories in the PATH variable from left to right.

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echo $PATH | tr ':' '\n'

Create a personal ~/bin directory and add it to the front of PATH so custom tools take priority.

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mkdir -p "$HOME/bin"
# add once to the end of ~/.bashrc
printf '
# add personal bin to PATH
export PATH="$HOME/bin:$PATH"
' >> "$HOME/.bashrc"
# reload the current shell
source ~/.bashrc

Create a small script and run it from anywhere.

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cat > "$HOME/bin/hi" <<'EOF'
#!/usr/bin/env bash
echo "Hi from $(hostname)"
EOF
chmod +x "$HOME/bin/hi"
hi

Variables and environment

Set a shell variable with name=value. Export it when child processes should see it.

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color=blue
export color
# or in one line
export color=blue

printenv | grep -i color || true

Persistent settings belong in ~/.bashrc so they load in new terminals.

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printf '
# custom color for demo
export COLOR_PREFERENCE="blue"
' >> ~/.bashrc
source ~/.bashrc

Aliases and small functions

Aliases shorten common commands and small functions automate simple tasks. Keep them in ~/.bashrc.

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cat >> ~/.bashrc <<'EOF'
# helpful aliases
alias ll='ls -alF'
alias la='ls -A'
alias l='ls -CF'
# function with one argument
mkcd() { mkdir -p "$1" && cd "$1"; }
EOF
source ~/.bashrc

Test them.

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ll
mkcd ~/playground/day2
pwd

Bypass an alias with a leading backslash.

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\ls -1

History and faster editing

History and completion speed up work.

• Up and Down: browse previous commands
• Ctrl R: search history; type a few letters and press Enter to run the match
• Tab: complete commands and paths; press Tab twice to see choices

Add timestamps to history entries.

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printf '
HISTTIMEFORMAT="%F %T "
' >> ~/.bashrc
source ~/.bashrc
history | tail -5

Redirection and pipes

Input and output redirection and pipes are core building blocks.

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# send output to a file (overwrite or append)
ls -la > listing.txt
ls -la >> listing.txt

# read input from a file
wc -l < listing.txt

# pipe output of one command into another
ps aux | grep ssh | grep -v grep

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mkdir -p ~/playground/day2 && cd ~/playground/day2
curl -s https://example.com | wc -c

Common mistakes and quick fixes

• Quote variables: prefer "$var"
• Avoid editing system files as root unless required; prefer sudo for single commands
• Check the source of a command with type -a <name> to see aliases and paths
• Read error messages; Bash often explains what went wrong
• Use -- to stop option parsing when a file name starts with a dash

Up next: Day 3 - Navigating the Filesystem and FHS

Day 3 focuses on the filesystem and the Linux directory layout. Learn fast navigation techniques and safe delete habits.