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Viewing File Contents

Linux provides powerful commands to view, inspect, and monitor file contents. Whether you're reading configuration files, analyzing application logs, or debugging production issues, mastering these commands is essential for every Linux administrator, DevOps Engineer, and Cloud Engineer.

Learning Path

Linux Mastery → Module 2: Linux Command Line Essentials → Lesson 5

Difficulty: Beginner

Reading Time: 25 Minutes

Course Progress

Course: Linux Mastery

Module: Linux Command Line Essentials

Lesson: 5 of 10

What You'll Learn

After completing this lesson, you'll be able to:

  • View file contents efficiently
  • Read large log files
  • Display specific lines from files
  • Monitor files in real time
  • Compare different file viewing commands
  • Choose the right command for different scenarios

Prerequisites

Before starting this lesson, complete:

  • Module 1 – Linux Fundamentals
  • Module 2 Lessons 1–4

Why Learn File Viewing Commands?

Linux systems store everything in files.

Examples include:

  • Configuration files
  • Application logs
  • Shell scripts
  • Kubernetes YAML files
  • Docker Compose files
  • Service logs

As a Linux administrator, reading files is one of the most common daily tasks.

Sample File

Throughout this lesson we'll use the following file.

Line 1: Linux
Line 2: Docker
Line 3: Kubernetes
Line 4: Terraform
Line 5: Ansible
Line 6: GitLab
Line 7: Jenkins
Line 8: Prometheus
Line 9: Grafana
Line 10: REBASH Academy

cat

The cat command displays the complete contents of a file.

Syntax

cat filename

Example

cat notes.txt

Display multiple files

cat file1 file2

Display line numbers

cat -n notes.txt

Useful when viewing:

  • Configuration files
  • Small scripts
  • README files

less

less is one of the most useful Linux commands.

Unlike cat, it lets you scroll through large files.

less logfile.log

Navigation

Key Action
Space Next Page
b Previous Page
↑ ↓ Scroll
/ Search
n Next Match
q Quit

Perfect for:

  • System logs
  • Large configuration files
  • Long text files

more

Older pager command.

more notes.txt

Displays one screen at a time.

Although still available, most Linux administrators prefer less.

head

Display the beginning of a file.

head notes.txt

Default:

First 10 lines

Display first five lines

head -5 notes.txt

Production example

head /var/log/syslog

tail

Display the end of a file.

tail notes.txt

Display last five lines

tail -5 notes.txt

Production example

tail /var/log/syslog

Real-Time Monitoring

One of the most useful Linux commands.

tail -f /var/log/syslog

Linux continuously displays new lines as they are written.

Widely used for:

  • Application logs
  • Kubernetes logs
  • Web server logs
  • Docker logs

Stop monitoring:

Ctrl + C

tac

Reverse of cat.

tac notes.txt

Displays the file from bottom to top.

Useful when newest information is at the end of the file.

nl

Display line numbers.

nl notes.txt

Output

1 Linux

2 Docker

3 Kubernetes

Useful when discussing specific lines in configuration files.

file

Determine the file type.

file notes.txt

Example output

ASCII text

Check executable

file /bin/ls

wc

Count lines, words and characters.

wc notes.txt

Example

10 10 90 notes.txt

Only count lines

wc -l notes.txt

Count words

wc -w notes.txt

strings

Display printable text from binary files.

strings binaryfile

Useful when investigating executables.

Command Comparison

Command Best Used For
cat Small files
less Large files
more Basic paging
head Beginning of file
tail End of file
tail -f Live log monitoring
tac Reverse output
nl Line numbers
file Identify file type
wc Count lines and words

Production Example

A web application is failing.

Check logs:

tail -50 /var/log/nginx/error.log

Monitor new errors:

tail -f /var/log/nginx/error.log

View configuration:

less /etc/nginx/nginx.conf

Verify line numbers:

cat -n /etc/nginx/nginx.conf

This workflow is common during production troubleshooting.

Production Perspective

These commands are used daily by engineers.

Examples

View Kubernetes YAML

cat deployment.yaml

Read Docker logs

less docker.log

Monitor application

tail -f application.log

Read configuration

less /etc/ssh/sshd_config

Count log entries

wc -l access.log

Hands-on Lab

Task 1

Create a file.

cat > commands.txt

Add:

Linux
Docker
Kubernetes
Terraform
Ansible
Git

Press:

Ctrl + D

Task 2

Display file.

cat commands.txt

Task 3

Display first three lines.

head -3 commands.txt

Task 4

Display last two lines.

tail -2 commands.txt

Task 5

Display line numbers.

nl commands.txt

Task 6

Count lines.

wc -l commands.txt

Task 7

Open using less.

less commands.txt

Quit:

q

Task 8

Display reverse order.

tac commands.txt

Command Deep Dive

Command Purpose Common Options Production Example
cat Display files -n View configuration
less Scroll files Search / Read logs
head Beginning -5 Verify headers
tail End -10 View recent logs
tail Live logs -f Monitor applications
nl Line numbers Default Debug configs
wc Count -l -w Count log entries
file File type Default Verify downloads

Mini Challenge

Create a file named:

linux-tools.txt

Add at least 10 Linux commands.

Now:

  • Display the first 5 lines.
  • Display the last 3 lines.
  • Count the number of lines.
  • Display line numbers.
  • View the file using less.
  • Display the file in reverse order.

Best Practices

  • Use less instead of cat for large files.
  • Use tail -f for monitoring logs.
  • Use head to inspect file headers.
  • Use wc to quickly summarize file contents.
  • Learn keyboard shortcuts in less.

Common Mistakes

❌ Using cat on huge log files.

✅ Use:

less logfile.log

or

tail logfile.log

❌ Opening multi-GB log files in editors.

✅ Use:

tail

head

less

❌ Forgetting to quit less.

✅ Use:

q

Interview Questions

Beginner

  1. What does cat do?
  2. Difference between head and tail?
  3. Which command monitors logs in real time?
  4. What is less used for?

Intermediate

  1. Why is less preferred over cat for large files?
  2. Explain tail -f.
  3. How do you count the number of lines in a file?
  4. What does the file command do?

Architect Level

  1. How would you investigate a production application that is generating errors?
  2. Which commands would you use to analyze a 5 GB log file?
  3. Why is tail -f essential for production monitoring?

Summary

In this lesson, you learned:

  • Displaying file contents
  • Reading large files
  • Viewing file headers and footers
  • Monitoring logs in real time
  • Counting lines
  • Identifying file types
  • Choosing the right command for different situations

These commands form the foundation of Linux troubleshooting and system administration.

Key Takeaways

  • cat is ideal for small files.
  • less is the preferred tool for large files.
  • head displays the beginning of a file.
  • tail displays the end of a file.
  • tail -f monitors log files in real time.
  • wc counts lines, words, and characters.
  • Choosing the right command improves productivity and troubleshooting efficiency.

What's Next?

Searching Files and Directories

In the next lesson, you'll learn:

  • find
  • locate
  • which
  • whereis
  • type
  • Searching by name, size, permissions, owner, and modification time
  • Real-world search techniques used by Linux administrators