Paul, I think Britanicca would appreciate your efforts almost as much
as we do :'). Thanks! I have some reading to do. After all of the
replies, I feel like I would enjoy taking a class on just regular
expressions and shell programming, so if any of you have some
books/references at the tip of your tongues (keyboards), fire away!
Mario
>On Sun, Dec 30, 2001 at 03:39:59PM -0500, Mario Lombardo wrote:
>
>> In the thread subject 'A "whatis" catalog', I was once again
>> mystified by the use of the dot in Unix-like systems. I originally
>> thought the use of dot was merely to state "here" or "from here" as
>> in the example of filesytems use:
>>
>> ls .
>> sh ./myscript
>>
>> But the dot turned out to be more than that when I saw people using
>> it in other ways; most recently from Ed Centanni's REply to my
>> question with this as the best working model:
>>
>> apropos . | sort > mycatalog.txt
>> versus...
>> apropos * | sort > mycatalog.txt
>>
>> I don't understand the literal interpretation of the dot in this
>> example versus using an asterisk. Actually, an asterisk doesn't
>> discover as many commands as the dot. In fact, doing a search for
>> the command chfn doesn't come up in the asterisk solution, yet it
>> comes up in the dot solution. This seems opposite of what would work
>> in the DOS world--which is my background.
>>
>> URL reading sources are fine. I just want to understand how to
>> utilize this little gem in other ways...if there are any more.
>>
>> Thanks,
>> Mario
>
>The dot in front of a filename also signifies that the file is "hidden"
>from standard file-type commands like ls, cp and such. In the case
>above, this wouldn't apply, as the dot is _not_ part of the filename:
>./myscript (the filename is myscript in the ./ [this] directory; if it
>were hidden, it would be ./.myscript). In that case, it's exactly what
>you said-- "here" or "this directory".
>
>To make a long story short, "apropos ." gives you everything in the
>whatis file, because it treats the dot as a regular expression for "any
>character". And the star [inadvertantly] gets expanded by the shell to
>be all the files in your current directory, so you get the output of
>apropos against _each_ filename in your current directory. For a more
>complete explanation, read on.
>
>The man pages don't shed any light on the use of the apropos command
>with the dot or the star. However, apropos is a shell script, so you can
>look at the source to determine what it's doing. Apropos runs against
>the whatis files, wherever they are. In the case of Red Hat, that's
>/var/cache/man/whatis, $manpath/whatis ($manpath will generally be
>various directories, like /usr/share/man), and /usr/lib/whatis. The
>whatis files are compiled by the makewhatis program, which often runs
>as a cron job periodically to rebuild the whatis files. Whatis files are
>basically the output of man against each command there's a man page for.
>You can run "less /var/cache/man/whatis" and you'll see what I mean.
>
>Apropos basically runs a grep command (twice) against the whatis files
>that it finds, looking for whatever you've given it. If you give it a
>'z' (as in "apropos z") it will find every line in the whatis files that
>contains a 'z' and output them.
>
> >From some experimenting with star and dot, here is what I think is
>happening. With the dot (.), apropos (and grep) look for _anything_ in
>the whatis files. That is, it uses the dot as part of a regular
>expression. In that case, the dot would represent any character, so
>you'd get the whole contents of the whatis files. In the case of the
>star (*), I believe that before executing grep, the shell expands the
>star to include the filenames of all the files in the current directory.
>So what you get is something like:
>
>grep -ia thisfile thatfile theotherfile ... /var/cache/man/whatis
>
>assuming thisfile, thatfile, etc. are all files in your current
>directory. If your home directory is populated with a few files, you can
>test this by running
>
>apropos * > junk
>
>and then look at the junk file. You'll see that apropos attempted to run
>the grep against every file in your home directory. So, for example, if
>you have a "Mail" subdirectory in your home directory, you'll get the
>result of running "apropos mail" (apropos is case insensitive) along
>with similar output for each and every file in your home directory.
>
>(I don't really think apropos was intended to be run with the star. The
>behavior of the shell expanding the star prior to executing grep is
>inconsistent with the usual behavior of apropos. This may be material
>for a bug report.)
>
>All of this is based on experiments with the apropos command on a Red
>Hat 7.2 system (apropos from man 1.5i1), run from my home directory. If
>your apropos command is not the same as mine, YMMV.
>
>HTH,
>
>Paul
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