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🦉 FreeBSD Shell Basics

FreeBSD provides a robust shell environment with both traditional Bourne shell compatibility and modern enhancements. This guide covers essential shell concepts and FreeBSD-specific features.

🎯 Shell Environment Overview

Default Shell

FreeBSD uses different default shells depending on the version and user type:

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# Check current shell
echo $SHELL

# System default shell
ls -la /bin/sh  # Usually points to /bin/sh (POSIX shell)

# User default shell
grep "^username:" /etc/passwd  # Shows user's shell

# Change user shell
chsh -s /bin/tcsh username     # Change to tcsh
chsh -s /usr/local/bin/bash username  # Change to bash

Available Shells

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# List available shells
cat /etc/shells

# Common FreeBSD shells:
# /bin/sh      - POSIX compliant shell
# /bin/csh     - C Shell
# /bin/tcsh    - Enhanced C Shell
# /usr/local/bin/bash  - GNU Bash
# /usr/local/bin/zsh   - Z Shell
# /bin/ksh     - Korn Shell
# /bin/ksh93   - Korn Shell 93

🔧 Shell Configuration Files

Login Shell Configuration

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# System-wide configuration
/etc/profile           # Bourne shell family login
/etc/csh.login         # C shell family login

# User-specific configuration
~/.profile             # Bourne shell family
~/.login               # C shell family

# Shell-specific configuration
~/.bashrc              # Bash interactive
~/.bash_profile        # Bash login
~/.zshrc               # Zsh interactive
~/.cshrc               # C shell interactive

Shell Initialization Order

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# Bourne shell family (sh, bash, ksh, zsh in sh mode)
# Login shell:
# 1. /etc/profile
# 2. ~/.bash_profile (bash) or ~/.profile (sh/ksh)
# 3. ~/.bashrc (if sourced from .bash_profile)

# Non-login interactive shell:
# 1. ~/.bashrc

# C shell family (csh, tcsh)
# Login shell:
# 1. /etc/csh.cshrc
# 2. /etc/csh.login
# 3. ~/.cshrc
# 4. ~/.login

# Non-login interactive shell:
# 1. /etc/csh.cshrc
# 2. ~/.cshrc

📋 Environment Variables

FreeBSD-Specific Variables

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# System information
echo $HOSTTYPE          # Architecture (amd64, i386, etc.)
echo $OSTYPE            # Operating system (FreeBSD)
echo $MACHTYPE          # Machine type
echo $USER              # Current user
echo $HOME              # Home directory
echo $PATH              # Command search path

# FreeBSD-specific paths
echo $PREFIX            # /usr/local (default)
echo $LOCALBASE         # /usr/local (ports/packages)

# Shell configuration
echo $SHELL             # Current shell
echo $TERM              # Terminal type
echo $PAGER             # Default pager (more, less)
echo $EDITOR            # Default editor

Setting Environment Variables

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# Temporary variables (current session only)
export MYVAR="value"
MYVAR="value" export    # Alternative syntax

# Persistent variables in ~/.profile or ~/.bash_profile
echo 'export MYVAR="value"' >> ~/.profile

# System-wide variables in /etc/profile
# (requires root access)
echo 'export SYSTEM_VAR="value"' >> /etc/profile

# C shell syntax (in ~/.cshrc or ~/.login)
setenv MYVAR "value"

🔍 Command Line Editing

Line Editing Features

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# Emacs mode (default for most shells)
Ctrl+A                 # Beginning of line
Ctrl+E                 # End of line
Ctrl+B                 # Backward character
Ctrl+F                 # Forward character
Ctrl+P                 # Previous command (up arrow)
Ctrl+N                 # Next command (down arrow)
Ctrl+D                 # Delete character/Delete session
Ctrl+K                 # Kill to end of line
Ctrl+U                 # Kill to beginning of line
Ctrl+W                 # Kill word backward
Ctrl+Y                 # Yank (paste killed text)
Ctrl+R                 # Reverse search history
Ctrl+L                 # Clear screen
Tab                    # Command/file completion

# Vi mode (alternative)
set -o vi              # Enable vi mode in sh/bash
bindkey -v             # Enable vi mode in zsh

History Management

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# History navigation
!!                     # Previous command
!n                     # Command number n
!string                # Most recent command starting with string
!?string               # Most recent command containing string
^old^new               # Substitute in previous command

# History manipulation
history                # Show command history
fc                     # Fix command (edit and re-execute)
history -c             # Clear history
history -d n           # Delete history entry n

# History configuration
export HISTSIZE=1000          # History size
export HISTFILESIZE=2000      # History file size
export HISTCONTROL=ignoredups # Ignore duplicates

🛠️ File and Directory Operations

FreeBSD File System Features

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# Soft Updates (default in FreeBSD)
# Provides better performance and reliability

# UFS (Unix File System) features
tunefs -n enable /      # Enable soft updates
dump -0uf /backup/root.dump /  # Full filesystem backup
restore -rf /backup/root.dump  # Restore filesystem

# ZFS support (if installed)
zpool list              # List ZFS pools
zfs list                # List ZFS filesystems
zfs create tank/home    # Create ZFS filesystem

File Permissions and Attributes

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# Traditional permissions
chmod 755 filename      # Set permissions
chown user:group filename  # Change ownership
ls -l filename          # Show permissions

# FreeBSD extended attributes
ls -@ filename          # Show extended attributes
setextattr user key value filename  # Set extended attribute
getextattr -q user key filename     # Get extended attribute

# File flags (BSD-specific)
chflags schg filename   # Set system immutable flag
chflags sunlnk filename # Set system undeletable flag
ls -lo filename         # Show file flags

📊 Process Management

FreeBSD Process Control

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# Process viewing
ps aux                  # All processes
ps -auxwww              # Detailed view
top                     # Interactive process viewer
htop                    # Enhanced top (if installed)

# Process manipulation
kill PID                # Terminate process
kill -9 PID             # Force terminate
killall processname     # Kill by name
pkill pattern           # Kill by pattern matching

# FreeBSD-specific tools
procstat PID            # Detailed process information
fstat                   # Open files by process
sockstat                # Socket statistics

Job Control

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# Background processes
command &               # Run in background
jobs                    # List jobs
fg %n                   # Foreground job n
bg %n                   # Background job n
kill %n                 # Kill job n

# Process priority
nice -n 10 command      # Run with lower priority
renice 5 PID            # Change priority of running process

# Resource limits
ulimit -a               # Show all limits
ulimit -u 100           # Limit processes
ulimit -f 1000000       # Limit file size

🌐 Network Operations

FreeBSD Network Tools

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# Interface configuration
ifconfig                # Show all interfaces
ifconfig em0            # Show specific interface
ifconfig em0 inet 192.168.1.100  # Configure interface

# Network information
netstat -rn             # Routing table
netstat -an             # All connections
sockstat                # Socket statistics (FreeBSD specific)
arp -a                  # ARP table

# Network diagnostics
ping host               # ICMP ping
traceroute host         # Route tracing
dig domain              # DNS lookup
nslookup domain         # DNS query

Network Services

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# Service management
service sshd status     # Check SSH status
service nginx start     # Start web server
service postgresql restart  # Restart database

# FreeBSD-specific services
service -l              # List all services
service -r              # List running services
service -e              # List enabled services

# Configuration files
/etc/rc.conf            # Service enablement
/usr/local/etc/         # Third-party service configs

🎨 Shell Programming Features

FreeBSD Shell Extensions

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# Parameter expansion (sh/bash)
${var:-default}         # Use default if unset
${var:=default}         # Set and use default
${var:+value}           # Use value if set
${var#pattern}          # Remove from beginning
${var%pattern}          # Remove from end

# Command substitution
result=$(command)       # Modern syntax
result=`command`        # Traditional syntax

# Arithmetic expansion
result=$((expression))  # Arithmetic evaluation
let var=expression      # Variable assignment

Flow Control

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# Conditional statements
if [ condition ]; then
    # commands
elif [ condition ]; then
    # commands
else
    # commands
fi

# Case statements
case "$variable" in
    pattern1)
        # commands
        ;;
    pattern2|pattern3)
        # commands
        ;;
    *)
        # default commands
        ;;
esac

# Loops
for item in list; do
    # commands
done

while [ condition ]; do
    # commands
done

until [ condition ]; do
    # commands
done

🧪 Advanced Shell Features

Input/Output Redirection

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# Standard redirection
command > file          # Standard output to file
command < file          # Standard input from file
command 2> file         # Standard error to file
command >& file         # Both output and error to file
command >> file         # Append to file

# Here documents
cat << EOF
Multi-line input
Variable expansion: $HOME
EOF

# Here strings
command <<< "single line input"

# Process substitution
diff <(sort file1) <(sort file2)

Functions and Aliases

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# Function definition
my_function() {
    local arg1="$1"
    local arg2="$2"
    echo "Arguments: $arg1, $arg2"
}

# Function with local variables
calculate_sum() {
    local num1="$1"
    local num2="$2"
    local sum=$((num1 + num2))
    echo "$sum"
}

# Aliases
alias ll='ls -la'
alias grep='grep --color=auto'
alias ..='cd ..'

# Permanent aliases in ~/.bashrc or ~/.zshrc
echo "alias ll='ls -la'" >> ~/.bashrc

🔧 FreeBSD-Specific Tools

System Administration Tools

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# System information
uname -a                # System information
freebsd-version         # FreeBSD version
sysctl hw.physmem       # Physical memory
sysctl kern.hostname    # Hostname

# Package management
pkg info                # Installed packages
pkg search package      # Search packages
pkg install package     # Install package
pkg delete package      # Remove package

# Ports system
cd /usr/ports/category/port
make install clean      # Build and install from ports

# System monitoring
dmesg                   # Boot messages
vmstat                  # Virtual memory statistics
iostat                  # I/O statistics
systat                  # Interactive system monitor

Security Tools

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# File integrity
mtree -c -K sha256 -p /etc > /etc/mtree.conf  # Create manifest
mtree -f /etc/mtree.conf                      # Verify integrity

# Security auditing
pkg audit               # Check for vulnerable packages
portaudit -F            # Fetch vulnerability database
portaudit -a            # Audit installed packages

# Process monitoring
procstat -f PID         # File descriptors
procstat -j PID         # Jails
procstat -v PID         # Virtual memory

🎨 Customization Examples

Shell Prompt Customization

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# Bash prompt
PS1='\u@\h:\w\$ '       # Basic prompt
PS1='\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

# Zsh prompt
PROMPT='%n@%m:%~%# '    # Basic prompt
PROMPT='%F{green}%n%f@%F{blue}%m%f:%F{yellow}%~%f %# '

# C shell prompt
set prompt="%n@%m:%~ %# "

# Dynamic prompt with git branch
parse_git_branch() {
    git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/(\1)/'
}

PS1='\u@\h:\w \$(parse_git_branch)\$ '

Useful Shell Functions

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# Directory navigation
mkcd() {
    mkdir -p "$1" && cd "$1"
}

# Extract any archive
extract() {
    if [ -f "$1" ]; then
        case "$1" in
            *.tar.bz2) tar -xjf "$1" ;;
            *.tar.gz)  tar -xzf "$1" ;;
            *.bz2)     bunzip2 "$1" ;;
            *.gz)      gunzip "$1" ;;
            *.tar)     tar -xf "$1" ;;
            *.zip)     unzip "$1" ;;
            *.rar)     unrar x "$1" ;;
            *)         echo "Unknown archive format" ;;
        esac
    else
        echo "'$1' is not a valid file"
    fi
}

# Quick backup
backup() {
    if [ -f "$1" ]; then
        cp "$1"{,.bak}
        echo "Backup created: $1.bak"
    else
        echo "File not found: $1"
    fi
}

🧾 Summary Commands

Essential FreeBSD Commands

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# System information
uname -a                # System details
freebsd-version         # Version information
sysctl -a               # All system parameters

# Package management
pkg info                # Installed packages
pkg search term         # Search packages
pkg install package     # Install package

# Service management
service -l              # List services
service name start      # Start service
sysrc name_enable=YES   # Enable service

# Process management
ps aux                  # All processes
top                     # Process monitor
procstat PID            # Process details

# File operations
ls -@                   # Show extended attributes
chflags flags file      # Set file flags
mtree                   # File integrity

Shell Customization

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# Configuration files
~/.profile              # Bourne shell login
~/.bashrc               # Bash interactive
~/.zshrc                # Zsh interactive
~/.cshrc                # C shell interactive

# Environment variables
export PATH="/usr/local/bin:$PATH"  # Add local bin
export EDITOR=vim       # Set default editor
export PAGER=less       # Set default pager

🧾 See Also