What does tee do?

$ ls | tee files.txt

• lslist directory contents
• |pipe — send this command's output into the next command
• teecopy input to a file and pass it through to output too
• files.txtan argument passed to the command

$ make 2>&1 | tee -a build.log

• makebuild targets according to a Makefile
• 2>&1send error output to the same place as normal output
• |pipe — send this command's output into the next command
• teecopy input to a file and pass it through to output too
• -aappend to the file instead of overwriting it
• build.logan argument passed to the command