Using tee to create a log

[Alan Dayley]

How does the piped program know that it is piped?  I would think that all
it knows is that it is outputing to sdtout.  Who changes the data in the
pipe?  The shell?

Alan

At 01:33 PM 7/26/01 -0700, you wrote:
>On Jul 26,  1:03pm, Gorman, John wrote:
>
>> Here is an example: telnet hostname | tee hostname.log
>> 
>> What this does is telnet to host hostname and record the commands
>> and output from that into the currenct directory as the filename
>> hostname.log.
>> 
>> By the way, this is an excellent way to record your testing history,
>> or save your actions for someone who wants to follow what you did at
>> a later time.
>
>The problem with using tee for this purpose is that stdout is no
>longer connected to a tty (or even a pseudo-tty).  This means that
>some programs will behave quite differently than they would have had
>you not thrown the pipe in.
>
>A better way to capture this kind of output is to use ``script''...
>
>    ocotillo:kev$ script
>    Script started, file is typescript
>    ocotillo:kev$ echo foo
>    foo
>    ocotillo:kev$ exit
>    exit
>    Script done, file is typescript
>    ocotillo:kev$ cat typescript 
>    Script started on Thu Jul 26 13:27:14 2001
>    ocotillo:kev$ echo foo
>    foo
>    ocotillo:kev$ exit
>    exit
>
>    Script done on Thu Jul 26 13:27:24 2001
>
>An example of a program that behaves differently when it's connected
>to a terminal vs a pipe is ``ls''.  Try doing just ``ls'' and then
>``ls | cat'' (or even ``ls | tee'').  You'll find that that the former
>gives you a listing with multiple columns while the latter gives you
>a listing with a single column.
>
>Kevin
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