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Viewing Files

You can navigate a filesystem and create files. Now let's read them.

File Types

As written in the intro, file extensions are not interpreted by Linux. To check what a file actually is:

file file_name.jpg   # file_name.jpg: PNG

Viewing Files - "Read-Only" Commands

These commands are safe to use as they won't change your files.

cat - Print entire file to screen

The cat command (short for "concatenate") prints the entire content of a file to your terminal.

cat myfile.txt

Pros: Great for small files. Cons: Floods your screen with long files.

cat multiple files

You can combine files and even create new ones:

cat file1.txt file2.txt   # prints both files

Useful options

Option What it does Example
-n Number all lines cat -n script.py
-b Number non-blank lines only cat -b config.conf

less - Scroll through files page by page

less is a pager. It shows one page of text at a time. Perfect for long files like logs or configs.

less myfile.txt
Key Action
Space Move down one page
b Move up one page
↓ ↑ / j k Move line by line
/word Search for "word" (press n for next match)
q Quit and return to the prompt

less is more (it replaced an older command called more and added more functionalities). That's the joke.

head and tail - View just the beginning or end

These are useful for quickly checking files.

head file.txt

tail file.txt

Common Options

Option What it does
-n N Show N lines instead of the default 10
-f Follow a file in real-time (tail only)

Tip

tail -f shows new lines as they're added. Press Ctrl+C to stop following. Invaluable for watching live logs.

Command Options What it does
file - Identify file type
cat -n -b Print entire file (+ line numbers)
less - Scroll through file page by page
head -n N First N lines (default 10)
tail -n N -f Last N lines (default 10), follow live

less keys: Space (down page), b (up page), /word (search), q (quit)

Check Your Understanding

1. Viewing a long file

You have a log file with thousands of lines. You want to browse it page by page.

What command do you use?

Reveal Answer

less logfile.txt

2. Checking a config quickly

You just want to see the first 5 lines of a config file.

What command do you use?

Reveal Answer

head -n 5 config.conf

3. Watching a log in real-time

A program is writing to debug.log and you want to see new lines as they appear.

What command do you use?

Reveal Answer

tail -f debug.log (press Ctrl+C to stop)

4. Identifying a file

You have a file called unknown with no extension. You want to know what it actually is.

What command do you use?

Reveal Answer

file unknown