tee : 显示程序的输出并将程序输出复制到一个文件中。

Usage: tee [OPTION]... [FILE]...
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
 

example:

        env | tee -a 1.txt

        echo "----start install ..." 2>&1 |  tee -a 1.txt