1. Man手册

NAME
tee - read from standard input and write to standard output and files
SYNOPSIS
tee [OPTION]… [FILE]…
DESCRIPTION
Copy standard input to each FILE, and also to standard output.
-a, —append
append to the given FILEs, do not overwrite
-i, —ignore-interrupts
ignore interrupt signals
-p diagnose errors writing to non pipes
—output-error[=MODE]
set behavior on write error. See MODE below
—help display this help and exit
—version
output version information and exit
MODE determines behavior with write errors on the outputs:
‘warn’ diagnose errors writing to any output
‘warn-nopipe’
diagnose errors writing to any output not a pipe
‘exit’ exit on error writing to any output
‘exit-nopipe’
exit on error writing to any output not a pipe
The default MODE for the -p option is ‘warn-nopipe’. The default operation when —output-error is not
specified, is to exit immediately on error writing to a pipe, and diagnose errors writing to non pipe out‐
puts.

2. 常用组合

cmd 2>&1 | tee log