Redirection & Pipes

Streams & Redirection

Every process has three standard streams:

Stream	FD	Default
stdin	0	keyboard
stdout	1	terminal
stderr	2	terminal

Operator	Effect
`>`	Redirect stdout (overwrite)
`>>`	Redirect stdout (append)
`2>`	Redirect stderr
`&>`	Redirect stdout and stderr
`2>&1`	Send stderr to wherever stdout goes
`<`	Redirect stdin from a file
`\	`	Pipe stdout into another command's stdin
`tee`	Write to a file and pass through

$ command > out.log 2>&1        # both streams to one file
$ ls /nope 2> /dev/null         # discard errors
$ dmesg | grep -i error | tee errors.txt | wc -l

Exam trap: Order matters - > file 2>&1 works, but 2>&1 > file sends stderr to the old stdout (terminal), then only stdout to the file.