Thank you Stephen I now understand a bit better exactly what
pipes are in regards to Linux.
Wallace
Stephen Turner wrote:
>
> On Sat, 3 Mar 2001, Wallace Mills wrote:
>
> > Hi all,
> > I hope you can given me some pointers/help as to how to use the
> > mailstats program inconjunction with analog. I am using
> > maillog2commonlog with postfix as the mail program.
> > Reading the docs, it states to pipe the actual mail logs through
> > maillog2commonlog like so: maillog2commonlog < maillog. My
> > question is where does the output of this end up, does it
> > generate another file or ???? and how do I send this output (if
> > there is one) to analog.??
> > I'm sorry if this seems to be a very simple question but I can
> > not find any information re this form of the usage of pipes
> > anywhere including my own reference books. Even though I have
> > been using Linux for a few months now I still have a lot to
> > learn.
>
> Specific question :
> -----------------
>
> I haven't used maillog2commonlog, but I assume it outputs to standard
> output (stdout to its friends). You can either redirect stdout to a file
> like this:
> maillog2commonlog < maillog > outfile
> and then get analog to read that file:
> analog outfile
>
> Or you can use a pipe. A pipe just send the standard output of one program
> directly into the standard input of a second program, without having to
> write the file to the disk in between. This command would look like this:
> maillog2commonlog < maillog | analog -
> (The | represents the pipe. The - tells analog to read standard input
> instead of a file from disk).
>
> General discourse :)
> -----------------
>
> Pipes are well worth understanding. Once you're used to them, you can write
> a one-line command by stringing several pipes together. For example, which
> lines have been deleted between file1 and file2?
> diff file1 file2 | grep "^<" | less
> This may look scary at first, but I've managed to do it all at once instead
> of in three stages as you might have to on a lesser operating system.
>
> I would say that pipes -- together with the fact that all programs read and
> write plain text files not proprietary formats so that they can all talk to
> each other -- are one of the things that makes Unix really powerful.
>
> --
> Stephen Turner http://www.statslab.cam.ac.uk/~sret1/
> Statistical Laboratory, Wilberforce Road, Cambridge, CB3 0WB, England
> "Your account can only be used for a single internet session at any one
> time and for no more than 24 hours in any one day." (NTL terms of use)
>
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--
Wallace Mills MCSE MCP
System Administrator PC Ward co.
Fax +61 7 3376 1508
Mobile 0417 738 112
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