What cd does (and why it matters)

• cd changes your current working directory (where the shell is “standing”).

• It’s a shell built-in (not an external program), so it affects your current terminal session immediately.

pwd         # show where you are

cd /etc     # go to /etc

pwd

1) Basic moves

cd                # go to your HOME directory (same as: cd ~)

cd /              # go to filesystem root

cd ~/Downloads    # go to Downloads inside your home

cd ..             # go up one level (to the parent directory)

cd ../..          # go up two levels

cd -              # jump back to the previous directory (toggles)

• ~ expands to your home (e.g., /home/rohit).

• . = current directory, .. = parent directory.

2) Absolute vs relative paths

• Absolute: starts with / (e.g., /var/log) — works from anywhere.

• Relative: from where you are now (e.g., cd ../project/src).

3) Paths with spaces & special characters

Use quotes or backslashes:

cd "My Projects/sem1"

cd My\ Projects/sem1

4) Handy environment variables

• echo $HOME → your home directory

• echo $PWD → current directory (“print working directory”)

• echo $OLDPWD → previous directory (used by cd -)

5) Super useful: CDPATH

Let cd search preset folders so you can jump without typing full paths.

# Add to ~/.bashrc (then: source ~/.bashrc)

export CDPATH=".:$HOME:$HOME/projects:$HOME/lab"

cd linux101    # will jump to ~/lab/linux101 if it exists

Order matters (left to right).

6) Following or avoiding symlinks: -L vs -P (bash)

• Default (-L, logical): keep symlinks in your PWD.

• Physical (-P): resolve the real path on disk (no symlinks in PWD).

cd -P /var/www/current   # PWD becomes the real directory target, not the symlink

(If unsure, just remember: -P gives you the real path.)

7) Common errors (and quick fixes)

• No such file or directory → path typo; tab-complete to verify.

• Permission denied → you don’t have execute (x) on that dir; check ls -ld dir.

• Stuck at root or protected dirs → normal users can’t cd into some system folders.

8) Faster navigation tricks

Put these in ~/.bashrc:

alias ..='cd ..'

alias ...='cd ../..'

# go up N levels: up 3  -> cd ../../..

up() { local n=${1:-1}; while ((n--)); do cd ..; done; }

# quick jump bookmarks (simple)

alias cdl='cd ~/lab'

alias cdp='cd ~/projects'

Reload: source ~/.bashrc

9) Script best practices (you’ll use this a lot)

• Always quote variables so spaces don’t break paths.

• Check cd success (exit code) before continuing.

#!/usr/bin/env bash

set -Eeuo pipefail

# go to the script’s directory

cd "$(dirname "$0")"

# or safely enter a target and fail early if missing

target="$HOME/projects/os-lab"

if cd "$target"; then

  echo "Now in: $PWD"

else

  echo "Cannot enter $target" >&2

  exit 1

fi

10) Related commands you’ll pair with cd

pwd            # confirm where you are

ls -la         # list contents after moving

pushd / popd   # directory stack (nice for bouncing between dirs)

11) Mini-lab (10–15 min)

mkdir -p ~/lab/cd/{alpha,beta,"My Projects"}

cd ~/lab/cd/alpha && pwd

cd ../beta && pwd

cd -                  # back to previous dir (alpha)

cd "../My Projects"   # path with spaces

pwd

# Try CDPATH:

echo 'export CDPATH="$HOME:~/lab/cd"' >> ~/.bashrc

source ~/.bashrc

cd beta               # should work from anywhere now

Exam-ready bullets

• cd is a shell built-in to change the current directory.

• cd, cd ~ → HOME; cd .. → parent; cd - → previous dir.

• Absolute vs relative paths; quote paths with spaces.

• $PWD/$OLDPWD track current/previous dirs; CDPATH speeds navigation.

• cd -P uses the physical path (resolves symlinks).

Want a printable one-pager for your class with cd, pwd, and ls together? I can package it neatly.