When we executes a command in Linux/Unix shell then it displays the output on screen and if you want to capture the output also in a log file (text file) then you can use the tee command. The tee command generates the shell command output on screen and as well as in a text file.
The below example is given to run the ls command to list all files in a directory on the screen and also saves the output to a file ls123.log, which can be viewed later:
$ ls -altr /myfolder/files | tee /home/files/log/ls123.log
You can see in above command that pipe | is used to separate and add to tee command. Before pipe is a your command and after pipe is to log the output of a command in a log file.
Now you can move to directory /home/files/log/ to see the contents of a ls123.log file, generated from the command.