Standard-streams
Standard in, out, and error streams created when a command is run. They are
usefully for passing data between applications. Most CLI applications support
using stdin as in input and will create both stdout and stderr outputs,
allowing multiple commands to be chained together.
The streams behave like files and are given the following descriptors:
stdin: 0stdout: 1stderr: 2
These streams can be redirected using > or >> where > overwrites the file
and >> appends to the end. To redirect a specific stream, prepend the
operators with the stream descriptor.
# redirect stderr to error.log
python script.py 2> error.log
# redirect stdout and stderr
python script.py 1> output.txt 2> error.log
python script.py &> script.log
# discard streams
python script.py &> /dev/null
Streams can also be piped to the stdin of another command.
echo "Hello" | sed "s/Hello/World/"
Standard input can also be redirected.
cat << END
line one
line two
END