tee can split pipe so that you write to the standard output (most commonly the next stage of the pipe) and to a file (or named pipe) simultaneously.
tee [ -ai ] file_list
Options
The following options may be used to control how tee functions.
-a Appends the output to an existing file. If the file does not exist it will be created. Normally an existing file would be overwritten.
-i Ignore interrupts. If you press the Delete key, tee ignores the interrupt signal sent to it and continues processing.
Arguments
The following argument may be passed to the tee command.
file_list One or more files where tee writes copies of the input.
Example: Sort a file and save its output, then, print first unique 10 lines.
sort somefile.txt | tee sorted_file.txt | uniq -c | head 10 > top10.txt