NJEI

Posted on Dec 15

The Magic of Linux Text Editors

#vim #devops #linux #tutorial

The Magic of Linux Text Editors: vi/vim and sed for Editing Like a Pro

The Problem: Editing Files on Remote Servers

You SSH into a server. Need to edit a config file. No GUI. No VS Code. Just the terminal.

You open the file with vi and... nothing works. You're stuck. Can't exit. Can't save. Panic sets in.

Or you need to replace a word in 100 files. Opening each one manually? That'll take hours.

This is why vi/vim and sed exist. One for interactive editing, one for automated text transformation.

Understanding vi/vim

vi (visual editor) is on every Linux system. vim (vi improved) is the enhanced version with more features.

Two Modes: The Key Concept

vi/vim has two modes:

Command Mode (default) - Navigate, delete, copy, search
Insert Mode - Type text normally

This confuses beginners, but it's powerful once you understand it.

Starting vi/vim

vi filename      # Opens file in vi
vim filename     # Opens file in vim

You start in Command Mode.

Insert Mode: Adding Text

From Command Mode, press:

Insert at cursor position

i     # Insert mode at cursor

Insert with space

a     # Insert mode after cursor (adds space)

New line and insert

o     # New line below, enter insert mode
O     # New line above, enter insert mode (capital O)

Press ESC to return to Command Mode.

Command Mode: Navigation and Editing

Basic Movement

h     # Left
j     # Down
k     # Up
l     # Right

# Or use arrow keys

Deleting

x     # Delete character under cursor
dd    # Delete entire line
dw    # Delete word
D     # Delete from cursor to end of line

Undo

u     # Undo last change
Ctrl+r     # Redo

Replace

r     # Replace single character (type new char)
R     # Replace mode (keep typing to replace multiple chars)

Note: r can be unreliable for multiple characters. Use R for replacing continuously or use search/replace.

Search

/keyword     # Search forward for "keyword"
?keyword     # Search backward for "keyword"
n            # Next occurrence
N            # Previous occurrence

Copy and Paste

yy    # Copy (yank) current line
p     # Paste below cursor
P     # Paste above cursor (capital P)

# Copy multiple lines
3yy   # Copy 3 lines

Save and Exit

:w           # Save (write)
:q           # Quit (only if no changes)
:wq          # Save and quit
:wq!         # Save and quit (force)
:q!          # Quit without saving (discard changes)

# Shortcut for save and quit
Shift+ZZ     # Same as :wq

Important: Type these commands only in Command Mode (press ESC first).

Search and Replace in vim

While in Command Mode:

:%s/old/new/g     # Replace all occurrences in file
:%s/old/new/gc    # Replace all, with confirmation
:s/old/new/g      # Replace in current line only

Breaking down :%s/old/new/g:

: - Enter command
% - Apply to entire file
s - Substitute
/old/new/ - Replace "old" with "new"
/g - Global (all occurrences on each line)

Replace on Specific Lines

:1,10s/old/new/g      # Lines 1-10
:5s/old/new/g         # Line 5 only

Example: Change Variable Name

# Replace "userName" with "userId" everywhere
:%s/userName/userId/g

vi vs vim

vi - Original editor, basic features, always available

vim - Enhanced version with:

Syntax highlighting
Multiple undo levels
Split windows
Plugins
Better search/replace

Check out openvim.com for interactive vim tutorial.

Most systems have vim. If not:

sudo apt install vim     # Ubuntu/Debian
sudo yum install vim     # CentOS/RHEL

The sed Command: Stream Editor

sed (stream editor) transforms text non-interactively. Perfect for scripts and bulk operations.

Basic Syntax

sed 'command' filename

Find and Replace

# Replace first occurrence per line
sed 's/Name/NewName/' filename

# Replace all occurrences (global)
sed 's/Name/NewName/g' filename

# Replace and save to file (in-place)
sed -i 's/Name/NewName/g' filename

Important:

Without -i, output goes to screen (original file unchanged)
With -i, modifies file directly
/g flag makes it global (all occurrences on each line)

Delete Text

# Delete a specific word
sed 's/Name//g' filename

# Delete lines containing keyword
sed '/keyword/d' filename

# Delete empty lines
sed '/^$/d' filename

# Delete first two lines
sed '1,2d' filename

# Delete lines 5-10
sed '5,10d' filename

Replace Special Characters

# Replace tabs with spaces
sed -i 's/\t/ /g' filename

# Replace spaces with tabs
sed -i 's/ /\t/g' filename

Display Specific Lines

# Show lines 12-18
sed -n '12,18p' filename

# Show all except lines 12-18
sed '12,18d' filename

# Show first 10 lines (like head)
sed -n '1,10p' filename

Add Blank Lines

# Add blank line after each line
sed G filename

# Double-space the file
sed G filename > newfile.txt

Advanced Replace: Skip Lines

# Replace in all lines EXCEPT line 1
sed '1!s/word/newword/g' filename

# Replace in lines 10-20 only
sed '10,20s/word/newword/g' filename

Real-World Scenarios

Scenario 1: Update Configuration

You need to change a port number in a config file:

# Check current value
grep "port" /etc/app/config.yml

# Replace with sed
sed -i 's/port: 8080/port: 3000/g' /etc/app/config.yml

# Verify change
grep "port" /etc/app/config.yml

Scenario 2: Clean Log Files

Remove empty lines and lines with "DEBUG":

# Remove empty lines
sed -i '/^$/d' app.log

# Remove DEBUG lines
sed -i '/DEBUG/d' app.log

# Or chain them
sed -i '/^$/d; /DEBUG/d' app.log

Scenario 3: Bulk File Updates

Replace API endpoint in all JavaScript files:

# Find all .js files and replace
find . -name "*.js" -exec sed -i 's/api.old.com/api.new.com/g' {} \;

Scenario 4: Edit Config on Server

SSH into server and edit nginx config:

ssh user@server
sudo vim /etc/nginx/nginx.conf

# Press i to enter insert mode
# Make changes
# Press ESC
# Type :wq to save and exit

Scenario 5: Remove Comments

Remove lines starting with # (comments):

sed -i '/^#/d' script.sh

Combining vi/vim and sed

Use vi/vim for interactive editing. Use sed for automated changes.

When to Use vim

Editing single files
Need to see context
Making multiple different changes
Interactive work

When to Use sed

Batch processing multiple files
Scripted changes
Simple find/replace operations
Automated deployments

Example Workflow

# 1. Check what needs changing
grep "old_value" *.conf

# 2. Test sed command (without -i)
sed 's/old_value/new_value/g' config.conf

# 3. Apply to all files
sed -i 's/old_value/new_value/g' *.conf

# 4. Verify one file in vim if needed
vim config.conf

Quick Reference

vim Commands

Command	Action
`i`	Insert mode at cursor
`a`	Insert after cursor
`o`	New line below
`ESC`	Back to command mode
`x`	Delete character
`dd`	Delete line
`u`	Undo
`r`	Replace character
`/keyword`	Search
`yy`	Copy line
`p`	Paste
`:w`	Save
`:q`	Quit
`:wq`	Save and quit
`:q!`	Quit without saving
`Shift+ZZ`	Save and quit
`:%s/old/new/g`	Replace all

sed Commands

Command	Action
`sed 's/old/new/g' file`	Replace all
`sed -i 's/old/new/g' file`	Replace in-place
`sed '/keyword/d' file`	Delete lines with keyword
`sed '/^$/d' file`	Delete empty lines
`sed '1,5d' file`	Delete lines 1-5
`sed -n '10,20p' file`	Show lines 10-20
`sed 's/\t/ /g' file`	Tabs to spaces
`sed G file`	Double-space

Common Mistakes

Mistake #1: Forgetting to exit insert mode

You're typing commands but they appear as text. Press ESC first.

Mistake #2: Using sed without testing

# Wrong - modifies file immediately
sed -i 's/old/new/g' important_file.txt

# Right - test first
sed 's/old/new/g' important_file.txt
# Check output, then add -i

Mistake #3: Not escaping special characters

# Wrong
sed 's/http://old.com/http://new.com/g' file

# Right - escape forward slashes or use different delimiter
sed 's|http://old.com|http://new.com|g' file

Mistake #4: Forgetting the /g flag

# Only replaces first occurrence per line
sed 's/old/new/' file

# Replaces all occurrences
sed 's/old/new/g' file

Tips for Efficiency

Tip 1: Create backups before sed -i

# Create backup with .bak extension
sed -i.bak 's/old/new/g' file.txt

Tip 2: Use vim for learning, sed for automation

Learn editing in vim interactively. Once you know what to change, automate with sed.

Tip 3: Chain sed commands

# Multiple operations at once
sed -i '/^$/d; /DEBUG/d; s/old/new/g' file.txt

Tip 4: Vim line numbers

# In vim command mode
:set number        # Show line numbers
:set nonumber      # Hide line numbers

Practical Examples

Example 1: Update Database Connection

# Old: localhost
# New: db.server.com

sed -i 's/localhost/db.server.com/g' config.php

Example 2: Change All Ports

# Update port 8080 to 3000 in all configs
find /etc/app -name "*.conf" -exec sed -i 's/:8080/:3000/g' {} \;

Example 3: Remove Trailing Whitespace

sed -i 's/[[:space:]]*$//' file.txt

Example 4: Add Text to Beginning of Lines

# Add "# " to beginning of each line (comment out)
sed 's/^/# /' file.txt

Example 5: Replace in Specific Section

# Replace only in lines 10-50
sed '10,50s/old/new/g' file.txt

Key Takeaways

vim has two modes: Command (default) and Insert (press i)
ESC returns to command mode - Always remember this
:wq saves and quits - Or use Shift+ZZ
sed is for automation - Use -i to modify files
Test sed without -i first - Preview changes before applying
Use /g for global replace - Without it, only first occurrence changes
vim for interactive, sed for batch - Choose the right tool
Practice on openvim.com - Interactive vim tutorial

vim and sed aren't relics. They're essential tools for server management, automation, and efficient text editing. Master them and you'll edit files faster than anyone clicking through a GUI.

What's your most useful vim or sed command? Share your go-to editing tricks in the comments.