Text Editing, Redirection & Pipes

Writing to Files

The echo Command

echo prints text to the terminal (standard output):

echo "Hello, DevOps!"

Output Redirection

Redirect output to a file instead of the terminal:

# Write to file (overwrites existing content)
echo "First line" > myfile.txt
 
# Append to file (adds to end)
echo "Second line" >> myfile.txt

Operator	Behavior
`>`	Overwrite file contents
`>>`	Append to file

# Overwrite demonstration
echo "Line A" > demo.txt
echo "Line B" > demo.txt
cat demo.txt
# Output: Line B (Line A was overwritten)
 
# Append demonstration
echo "Line A" >> demo2.txt
echo "Line B" >> demo2.txt
cat demo2.txt
# Output: Line A
#         Line B

Redirect Any Command Output

Any command that prints to the terminal can be redirected:

# Save directory listing to a file
ls / > root_contents.txt
 
# Save system info
uname -a > system_info.txt
 
# Append date to a log
date >> activity.log

Reading Files

# Display entire file
cat myfile.txt
 
# Display first N lines
head -n 5 myfile.txt
 
# Display last N lines
tail -n 3 myfile.txt
 
# Follow a file in real-time (great for logs)
tail -f /var/log/syslog

Text Editors

Nano (Beginner-Friendly)

nano myfile.txt

Essential nano shortcuts:

Shortcut	Action
`Ctrl+O`	Save file
`Ctrl+X`	Exit
`Ctrl+K`	Cut line
`Ctrl+U`	Paste line
`Ctrl+W`	Search
`Ctrl+Y/V`	Page up/down

Vim (Power User)

vim myfile.txt

Vim has modes:

Normal mode (default) — navigate and execute commands
Insert mode — type text (press i to enter)
Command mode — save, quit (press :)

Essential vim commands:

Command	Action
`i`	Enter insert mode
`Esc`	Return to normal mode
`:w`	Save
`:q`	Quit
`:wq`	Save and quit
`:q!`	Quit without saving
`dd`	Delete line
`yy`	Copy line
`p`	Paste

💡

For DevOps work, nano is fine for quick edits. Learn vim basics too — it's available on virtually every Linux server.

I/O Streams

Linux has three standard streams:

Stream	Descriptor	Default
stdin (input)	0	Keyboard
stdout (output)	1	Terminal
stderr (error)	2	Terminal

Redirecting Errors

# Redirect errors to a file
cat nonexistent_file 2> errors.log
 
# Redirect both output and errors
ls /root > output.txt 2> errors.txt
 
# Redirect both to the same file
ls /root > all_output.txt 2>&1
 
# Discard errors completely
command_that_might_fail 2> /dev/null

Input Redirection

# Feed file contents as input
sort < unsorted_list.txt
 
# Combine input and output redirection
sort < unsorted.txt > sorted.txt

Pipes

The pipe operator | sends the output of one command as input to another:

# Find files containing "bin" in root listing
ls / | grep bin
 
# Count number of files in a directory
ls | wc -l
 
# Find a specific process
ps aux | grep nginx
 
# Chain multiple pipes
ls / | grep bin | head -n 1

Common Pipe Patterns

# Sort and remove duplicates
cat names.txt | sort | uniq
 
# Search logs for errors
cat /var/log/syslog | grep -i error | tail -n 20
 
# Count lines matching a pattern
grep -c "404" access.log

Chaining Commands

Sequential Execution (&&)

Run the next command only if the previous one succeeds:

# Update and install (second runs only if first succeeds)
sudo apt update && sudo apt install nginx
 
# Create directory and enter it
mkdir project && cd project

Run Regardless (;)

# Run both commands regardless of success/failure
echo "Starting..." ; ls /nonexistent ; echo "Done"

Run on Failure (||)

# Run second command only if first fails
ping -c 1 google.com || echo "Network is down"

The grep Command

grep searches for patterns in text — one of the most useful Linux commands:

# Search for a word in a file
grep "error" logfile.txt
 
# Case-insensitive search
grep -i "warning" logfile.txt
 
# Search recursively in directories
grep -r "TODO" ./src/
 
# Show line numbers
grep -n "function" script.sh
 
# Invert match (show lines NOT matching)
grep -v "debug" logfile.txt

Summary

> overwrites, >> appends output to files
cat, head, tail read file contents
nano for quick edits, vim for power users
2> redirects errors, 2>&1 combines stdout and stderr
| pipes output between commands
&& chains commands (run next only on success)
grep searches text with powerful pattern matching

Next Steps

In the next lesson, we'll cover users, groups, permissions, and environment variables — essential for securing Linux systems.

Learning Objectives