What ls does

ls shows the contents of a directory. By default it lists the current directory, but you can give it paths or patterns.

ls            # list current folder

ls /etc       # list a specific folder

ls *.py       # list files matching a pattern (shell expands the *.py)

Most-used options (with tiny examples)

ls -a         # include hidden files (names starting with .)

ls -A         # like -a but hides . and ..

ls -l         # “long” listing (permissions, owner, size, time)

ls -lh        # long listing with human-readable sizes (K, M, G)

ls -la        # long + all (common)

ls -alh       # order of flags doesn’t matter

ls -t         # sort by modified time (newest first)

ls -tr        # reverse (oldest first)

ls -S         # sort by size (largest first)

ls -X         # sort by extension

ls -U         # don’t sort (fast on huge dirs)

ls -R         # recursive listing (subdirectories too)

ls -d */      # list directory names themselves (not their contents)

ls -F         # classify: add / for dirs, * for executables, @ for symlinks

ls --color=auto   # colored output (often already default on Linux)

ls --group-directories-first   # puts folders before files (GNU ls)

Tip: Many systems define ll as an alias for ls -alF. Try type ll to see.

Reading the long listing (ls -l)

Example line:

-rwxr-x---  1 alice devs  1256 2025-10-08  script.sh

^ ^^^ ^^^   ^  ^     ^     ^        ^          ^

| |   |     |  |     |     |        |          └─ name

| |   |     |  |     |     |        └─ modified time

| |   |     |  |     |     └─ size (bytes; add -h for KB/MB)

| |   |     |  |     └─ group

| |   |     |  └─ owner

| |   |     └─ hard link count

| |   └─ permissions for group (r=read, w=write, x=execute)

| └─ permissions for owner

└─ type/others: '-' file, 'd' directory, 'l' symlink, 'c' char dev, 'b' block dev, 's' socket, 'p' fifo

Practical combos you’ll actually use

ls -lah                      # everything, detailed, human sizes

ls -lt | head                # 10 most recently modified items

ls -l --time-style=long-iso  # ISO timestamps (GNU ls)

ls -al --group-directories-first

ls -1                        # one entry per line (good for scripts)

Patterns (globbing) & quoting

• *.c matches all .c files (the shell expands this before ls runs).

• Quote to prevent the shell from expanding (to see the literal pattern):

·         ls "*.c"   # passes the asterisk to ls literally

Hidden files and “dotfiles”

• Files starting with . are hidden (e.g., .bashrc, .gitignore).

• Use -a or -A to see them:

·         ls -A ~

Performance & safety tips

• On very large folders, unsorted is faster: ls -U.

• Avoid parsing ls in scripts (spaces/newlines in names can break logic). Prefer:

·         find . -maxdepth 1 -print0 | xargs -0 -I{} printf '%s\n' "{}"

• If names contain spaces, quote variables: ls "$dir".

Common gotchas (Linux vs macOS)

• Linux (GNU coreutils) supports --group-directories-first, --time-style.

• macOS/BSD ls differs: color uses -G (not --color), and some GNU options aren’t available. You can install GNU coreutils (gls) via Homebrew if needed.

Mini-lab (10–15 minutes)

mkdir -p ~/lab/ls && cd ~/lab/ls

touch a.txt b.txt ".hidden" script.sh

chmod +x script.sh

dd if=/dev/zero of=big.bin bs=1M count=5 2>/dev/null

ls

ls -a

ls -lh

ls -lt

ls -S

ls -F

ls -d */  # create a dir and try again: mkdir data; ls -d */

Quick reference

• List all: ls -a

• Detailed: ls -l (add -h for sizes)

• Newest first: ls -lt

• Largest first: ls -lS

• Folders first: ls --group-directories-first (GNU)

• Recursive: ls -R

• Show types: ls -F

Want this as a one-page printable sheet for your class? I can format it nicely.