04 Viewing File Content

Learning objectives

• View a text file directly.
• Page through large files.
• View a file’s beginning, end, and live appended content.

Command overview

Command	Purpose	Meaning	Basic usage	Example
cat	Print an entire file	Short for concatenate; commonly prints a small file directly	cat file	cat README.md
less	Page through a file	Suitable for browsing a large file, with scrolling and search	less file	less app.log
head	View a file’s beginning	Shows the first 10 lines by default	head [options] file	head -n 20 app.log
tail	View a file’s end	Shows the final 10 lines by default and can follow changes	tail [options] file	tail -f app.log
wc	Count newlines, words, bytes, or characters	By default shows newline, word, and byte counts; -m counts characters	wc [options] file	wc -l app.log

Common scenarios

View a small file:

cat config.txt

Page through a large log:

less app.log

View the beginning and end:

head -n 20 app.log
tail -n 50 app.log

Follow newly appended log content:

tail -F -- app.log

Count lines in a file:

wc -l app.log

Notes for beginners

• cat is not suitable for opening a very large log directly because it can flood the terminal.
• In less, press /keyword to search, n for the next match, and q to quit.
• tail -f occupies the terminal continuously; press Ctrl-c to stop it.
• GNU tail -F retries by name and handles common log rotation. Options are not identical on every platform.
• wc -l counts newline characters; the final text segment without a trailing newline does not increase that count. wc -c counts bytes and wc -m counts characters.
• Logs can contain user input, tokens, internal addresses, and command lines. Do not publish an entire log directly.

Log-viewing exercise

On the fictional log from the integrated project, compare head -n 2, tail -n 2, wc -l, and less. State what range each command reads, whether it keeps running, and whether its output belongs in a report.

References

• GNU Coreutils wc
• GNU Coreutils tail