1. touch — Create Empty Files or Update Timestamps
Creates an empty file or updates a file's timestamps.
Syntax
touch [options] <file>
Common Usage
touch file.txt # Create an empty file
touch file1.txt file2.txt # Create multiple files
touch existing.txt # Update timestamps
touch file{1..5}.txt # Create file1.txt ~ file5.txt
Useful Options
touch -a file.txt # Update access time (atime)
touch -m file.txt # Update modification time (mtime)
touch -c file.txt # Do not create the file if it doesn't exist
touch -d "2026-07-04 12:30:00" file.txt
touch -t 202607041230 file.txt
touch -r source.txt target.txt # Copy timestamps from another file
Timestamp Types
- atime : Last access time
- mtime : Last modification time
- ctime : Last metadata (status) change
View timestamps:
stat file.txt
2. cat — Display and Concatenate Files
Displays file contents or combines multiple files.
Syntax
cat [options] <file>
Common Usage
cat file.txt
cat file1.txt file2.txt
cat file1.txt file2.txt > combined.txt
Create or Append Files
cat > new_file.txt # Create or overwrite
cat >> file.txt # Append to an existing file
Press Ctrl + D to save and exit.
Useful Options
cat -n file.txt # Show line numbers
cat -b file.txt # Number non-empty lines only
cat -s file.txt # Squeeze multiple blank lines
cat -E file.txt # Show end-of-line markers ($)
cat -A file.txt # Show all non-printing characters
Notes
Avoid using cat for very large files. Instead, use:
head file.txt
tail file.txt
less file.txt
3. less — View Large Files Efficiently
Displays large files one screen at a time without loading the entire file into memory.
Syntax
less file.txt
Exit with:
q
Navigation
| Key | Action |
|---|---|
j / ↓ |
Next line |
k / ↑ |
Previous line |
Space / PgDn
|
Next page |
b / PgUp
|
Previous page |
g |
First line |
G |
Last line |
Search
/keyword Search forward
?keyword Search backward
n Next match
N Previous match
Useful Options
less -N app.log # Show line numbers
less -i app.log # Case-insensitive search
less +F app.log # Follow file like tail -f
ps -ef | less # View command output page by page
Notes
- Press Ctrl + C to exit follow mode (
+F). - Press Shift + F to resume following.
4. head — Display the Beginning of a File
Prints the first part of a file.
By default, head displays the first 10 lines.
Syntax
head [options] <file>
Common Usage
head file.txt
head -n 5 file.txt
head -5 file.txt
head -c 20 file.txt
Useful Options
head -q file1.txt file2.txt # Hide file headers
head -v file.txt # Always show file header
Practical Examples
Display lines 11–15:
head -n 15 system.log | tail -n 5
Show the five most recently modified files:
ls -lt | head -n 6
5. tail — Display the End of a File
Prints the last part of a file.
By default, tail displays the last 10 lines.
Syntax
tail [options] <file>
Common Usage
tail file.txt
tail -n 5 file.txt
tail -5 file.txt
tail -n +20 file.txt
Real-Time Monitoring
tail -f app.log # Follow file updates
tail -F app.log # Continue following after log rotation
tail -f app.log --pid=1234 # Stop when process exits
Stop monitoring with Ctrl + C.
Useful Options
tail -n 30 file.txt
tail -c 100 file.txt
Practical Examples
Monitor only error messages:
tail -f app.log | grep "ERROR"
Notes
-
-ffollows a file as it grows. -
-Fis preferred for log files because it handles log rotation automatically.
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