Zsh Lesson 4: View and Edit Files — cat, less, head, tail, nano

cat file dumps contents. head -N file first N lines, tail -N file last N. less file opens a pager (q to quit, / to search). nano file for a simple terminal editor. Redirection > writes, >> appends.

You can read files without leaving the terminal. Five commands cover almost everything.

cat: dump file contents

echo 'Hello, World!' > greeting.txt
echo 'This is line 2' >> greeting.txt
echo 'This is line 3' >> greeting.txt

cat greeting.txt
# Hello, World!
# This is line 2
# This is line 3

cat path prints the whole file to the terminal. Short for "concatenate" — really designed for joining multiple files:

cat file1.txt file2.txt > combined.txt

For a single file, it's just "dump it."

cat -n adds line numbers:

cat -n greeting.txt
#      1  Hello, World!
#      2  This is line 2
#      3  This is line 3

For huge files, don't cat them — they'll fill your terminal. Use less or head/tail instead.

Redirection: > and >>

echo 'first line' > file.txt     # OVERWRITES
echo 'second line' >> file.txt   # APPENDS

• > — write stdout to file. Truncates the file first.
• >> — append stdout to file.

# Save command output to a file
ls -la > listing.txt
date > timestamp.txt

# Append to a log
echo "$(date): user logged in" >> activity.log

Lesson 16 covers redirection in depth (stderr, /dev/null, here-docs).

head: first N lines

seq 30 | xargs -I{} echo 'Line {}: Content' > numbers.txt

head numbers.txt
# (first 10 lines — default)

head -5 numbers.txt
# (first 5)

head -N file prints the first N lines. Default N is 10.

For first N bytes:

head -c 100 file.bin

tail: last N lines

tail numbers.txt
# (last 10 lines — default)

tail -5 numbers.txt
# (last 5)

Most useful for logs:

tail /var/log/system.log

For watching a file as it grows (live tail):

tail -f /var/log/system.log
# follows updates — Ctrl-C to stop

-f follows the file. -F is similar but reopens the file if rotated. Essential for log debugging.

head + tail = "lines N-M"

head -15 numbers.txt | tail -5
# (lines 11-15)

The classic Unix idiom: pipe head to tail for a window in the middle of a file.

less: the pager

For files larger than your screen:

less longfile.txt

Opens an interactive pager. Inside less:

• SPACE — next page.
• b — previous page.
• j / k — down/up one line.
• /word then Enter — search forward.
• ?word then Enter — search backward.
• n — next match.
• N — previous match.
• g — top.
• G — bottom.
• q — quit.

Same keys as man. Once you internalize them, navigation is faster than scrolling.

less is preferred over more (an older, less-featured pager). They share most key bindings.

wc: count lines, words, bytes

wc longfile.txt
#  50  150  900 longfile.txt
# (lines, words, characters)

wc -l longfile.txt
# 50 longfile.txt

Quick way to get a file's size in lines.

nano: terminal editor

nano myfile.txt

Opens myfile.txt in nano, a beginner-friendly terminal editor. Inside nano:

• Type — your text.
• Ctrl-O then Enter — write (save).
• Ctrl-X — exit (prompts to save if modified).
• Ctrl-K — cut current line.
• Ctrl-U — paste.
• Ctrl-W — search.
• Ctrl-G — help (full keybindings).

nano shows the most-used shortcuts at the bottom of the screen — ^ means Ctrl. So ^X Exit means "Ctrl-X to exit."

For more powerful editing, learn vim (or nvim) eventually — way more keystrokes, way more leverage. But nano is fine for quick edits.

Other editors

vim file.txt          # vim — modal, powerful, steep learning curve
nvim file.txt         # neovim — modern vim
code file.txt         # VS Code (if installed)
open -a "TextEdit" file.txt   # macOS GUI app

For shell scripting, terminal editors (nano, vim, nvim) are best. They keep you in the same window.

Working with file contents

A typical pipeline:

# How many lines start with "ERROR" in a log?
grep "^ERROR" logfile.txt | wc -l

# What are the most recent 20 entries?
tail -20 logfile.txt

# Show me lines 100-110 of a config
head -110 config.yaml | tail -11

# Dump a small file
cat ~/.zshrc

# Browse a long file
less /etc/services

Each command does one thing; pipes connect them.

Binary files

cat and less are for text. For binary (images, executables):

# DON'T do this — corrupts your terminal:
cat photo.jpg

# Use file to inspect type
file photo.jpg
# photo.jpg: JPEG image data, ...

# Use hexdump for raw bytes
hexdump -C photo.jpg | head

If you accidentally cat a binary and get garbage in the terminal, type:

reset

Or close and reopen the terminal.

Common stumbles

cat on a huge file. Fills the terminal, scrolls forever. head -100 or less instead.

> overwrites without warning. command > file always truncates file first. To prevent accidents, set noclobber:

setopt noclobber
echo new > existing.txt    # zsh: file exists: existing.txt
echo new >| existing.txt   # force-overwrite

head -5 on Linux vs head -n 5. Both work on macOS. The -n 5 form is POSIX; the -5 form is more common in shell.

tail -f on a non-rotating file. Hangs forever. Ctrl-C to stop.

Forgot -r for cat? No — cat doesn't have a recursive option. For "dump every file in a directory," use find:

find . -type f -exec cat {} \;

Editor save doesn't work. Permission denied → file owned by another user. Use sudo nano file.

less doesn't quit. Press q. If stuck, Ctrl-C then q.

What's next

Lesson 5: customizing Zsh. Aliases, env vars, PROMPT, .zshrc.

Recap

cat file dumps; head -N first N lines, tail -N last N; head | tail for middle. less file pages (q quits, / searches). nano file for simple editing (Ctrl-O save, Ctrl-X exit). Redirection: > writes (truncates), >> appends. wc -l file for line count. For huge files, never cat — use less or head/tail.

Next lesson: customizing Zsh.