> outputFile, empty file

set -o noclobber, avoid to overwrite existing file

cat test > testFile, redirect output to a file

ls -al | more, pipe

>>, append text to existing file

IO stream number

• standard input: 0
• standard output: 1
• standard error: 2
• program-name 2> error.log, redirect program error to a file
• ls > dirlist 2>&1, redirect error to standard output
• make all 2> /dev/pts/0, redirect errors to standard output, suppose tty is /dev/pts/0