Redirection

Standard Output

frequently abbreviated as stdout
redirection represented with >
used to redirect the result of a command somewhere else
the contents of the file are overwritten when using >
can use >> to append to the contents of a file

Examples

Output the results of one command to a file
```
echo "print('hello world')" > hello.py
```
Output and concatenate the results to a new line in the file
```
echo "print('another line')" >> hello.py
```

Output but erase the contents of hello.py

echo "print('erase that old stuff')" > hello.py

Standard Input

frequently abbreviated as stdin
redirection represented with <
can be used to provide input into a program

Example

Create a file named name.txt that contains your name.

echo "josh" > name.txt   # create a file named name.txt that contains your name

Open a text editor
```
vim greeting.py   # or nano greeting.py
```

Add the following code to the file.

import sys
name = sys.stdin.read()
print(f"Hi {name}")

Save and close the file.
Feed the contents of the name.txt file into the greeting.py file while running the python file.
```
python3 greeting.py < name.txt
```

Standard Error

Frequently abbreviated as stderr
represented with 2>
can append with 2>>
if an error is produced, you can use this to redirect the error elsewhere, like a log file for errors

Examples

notarealcommand 2> error-file.txt
notarealcommand 2>> error-file.txt

Pipe

represented with |
creates a “pipe” or “pipeline” between two programs
takes the output of the one command and uses it as input it into another command

Example

List the contents of /usr/bin, but use more to view them in a paginated way.

ls -al /usr/bin | more