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 Forum index » House Training » Users ( For the regulars )
Redirection with 'tee' - having your cake and eating it too.
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tallboy


Joined: 21 Sep 2010
Posts: 447
Location: Oslo, Norway

PostPosted: Sat 09 Feb 2013, 13:38    Post_subject:  Redirection with 'tee' - having your cake and eating it too.  

There is a very useful command named 'tee', that I don't see mentioned very often. I have gathered some info here.
Unix/Linux borrows an idea here from the plumbing trade. This is a redirection operator, but with a difference. Like the plumber's 'tee', it permits 'siphoning off' to a file the output of a command or commands within a pipe, but without affecting the result. This is useful for printing an ongoing process to a file or paper, perhaps to keep track of it for debugging purposes.

The `tee' command copies standard input to standard output and also to any files given as arguments. This is useful when you want not only to send some data down a pipe, but also to save a copy.

Synopsis: tee [OPTION]... [FILE]...

Examples:
Code:
cat listfile* | sort | tee check.file | uniq > result.file

Here, the file 'check.file' contains the concatenated sorted "listfiles", before the duplicate lines are removed by uniq, and the result of that operation is sent to 'result.file'.

Code:
ls /root | tee my_directories.txt

Lists the files (displays the output on the screen) and also sends the output to a file: 'my_directories.txt'. (puppy specific - the original would be /home/username instead of /root)

You can also write the output to multiple files as shown below.
Code:
ls | tee file1 file2 file3



Note:
  • If a file being written to does not already exist, it is created.
  • By default tee command overwrites the file.You can instruct the 'tee' command to append to the file using the option –a as shown below.
    `-a' `--append' Append standard input to the given files rather than overwriting them.
    Code:
    ]ls | tee –a file


tallboy

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