I/O & Redirection

1. Input/Output (I/O)

I/O operations typically involve three data streams: Standard Input (stdin), Standard Output (stdout), and Standard Error (stderr).

2. Redirecting Output

The > operator redirects the output of a command to a file.

ls > files.txt

List files and save the list to a file

3. Appending Output

Use » to add output to an existing file without deleting the current content.

date >> disk_usage.txt; df -h >> disk_usage.txt

Collect the free disk space on your system every hour.


4. Redirecting Errors

2> redirects error messages.

ls /nonexistent_directory 2> errors.txt

5. Combining Outputs

Combine stdout and stderr into one stream using >&.

find / -name "*.jpg" > all_jpg_files.txt 2>&1

6. Input Redirection

Use < to provide input to programs.

mysql -u username -p database_name < queries.sql

Provide SQL commands via a file

7. Piping in Linux

Piping | lets you use the output of one command as input for another.

cat all_jpg_files.txt | grep "/home/"