Piping and Redirection
There are STDIN(0), STDOUT(1) & STDERR(2):
| Stream Name | Description |
|---|---|
| Standard Input (STDIN) | Data fed into the program |
| Standard Output (STDOUT) | Output from the program (defaults to terminal) |
| Standard Error (STDERR) | Error messages (defaults to terminal) |
We can use |, < or > to pass any of the 3 streams to other programs:
Redirecting to a New File
echo "test" > file.txt- if the file already exists it is overwritten!
Redirecting to an Existing File
- to append to a file use
>>echo "test" >> file.txt
Redirecting from a File
echo < file.txt
Redirecting STDERR
ls ./none-existent-file.txt 2>error.txt
Piping
cat error.txt | wc -m
Relevant Note(s): Linux Basics