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<TITLE>The Answer Gang 62: about Unix command rm</TITLE>
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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
height="50" width="60" alt="(?) " border="0"
>about Unix command rm</H3>
<p><strong>From Jane Liu
</strong></p>
<p align="right"><strong>Answered By Mike Orr, Ben Okopnik, Dan Wilder
<br></strong></p>
<!-- sig -->
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
I have a question about rm command. Would you please tell me how to remove
all the files excepts certain files like anything ended with .c?
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Mike]
The easiest way (meaning it will work on any Unix systems anywhere), is
to move those files to a temporary directory, then delete "everything",
then move those files back.
</BLOCKQUOTE>
<blockquote><code><font color="#000033"><br>mkdir /tmp/tdir
<br>mv *.c /tmp/tdir
<br>rm *
<br>mv /tmp/tdir/* .
<br>rmdir /tmp/tdir
</font></code></blockquote>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Ben]
The above would work, but seems rather clunky, as well as needing a lot of
typing.
</blockquote>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Mike]
Yes, it's not something you'd want to do frequently. However, if you don't
know a lot about Unix commands, and are hesitant to write a shell script
which deletes a lot of files, it's a good trick to remember.
</BLOCKQUOTE>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Ben]
It's true that it is completely portable; the only questionable
part of my suggestion immediately below might be the "-1" in the "ls", but
all the versions of "ls" with which I'm familiar support the "single column
display" function. It would be very easy to adapt.
</BLOCKQUOTE>
<BLOCKQUOTE>
My preference would be to use something like
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
rm $(ls -1|grep -v "\.c$")
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
because the argument given to "grep" can be a regular expression. Given
that, you can say things like "delete all files except those that end in
'htm' or 'html'", "delete all except '*.c', '*.h', and '*.asm'", as well as
a broad range of other things. If you want to eliminate the error messages
given by the directories (rm can't delete them without other switches), as
well as making "rm" ask you for confirmation on each file, you could use
a "fancier" version -
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
rm -i $(ls -AF1|grep -v "/$"|grep -v "\.c$")
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
Note that in the second argument - the only one that should be changed -
the "\" in front of the ".c" is essential: it makes the "." a literal
period rather than a single-character match. As an example, lets try the
above with different options.
</BLOCKQUOTE>
<BLOCKQUOTE>
In a directory that contains
</BLOCKQUOTE>
<blockquote><code><font color="#000033"><br>testc
<br>test-c
<br>testcx
<br>test.cdx
<br>test.c
</font></code></blockquote>
<BLOCKQUOTE>
".c" means "'c' preceded by any character" - NO files would be deleted.
</BLOCKQUOTE>
<BLOCKQUOTE>
"\.c" means "'c' preceded by a period" - deletes the first 3 files.
</BLOCKQUOTE>
<BLOCKQUOTE>
"\.c$" means "'c' preceded by a period and followed by the end of the line"
- all the files except the last one would be gone.
</BLOCKQUOTE>
<BLOCKQUOTE>
Here's a script that would do it all in one shot, including showing a list
of files to be deleted:
</BLOCKQUOTE>
<blockquote>See attached
<a href="../misc/tag/rmx.bash.txt">misc/tag/rmx.bash.txt</a></blockquote>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Dan]
Which works pretty well up to some limit, at which things
break down and exit due to $skip being too long.
</BLOCKQUOTE>
<BLOCKQUOTE>
For a less interactive script which can remove inordinate
numbers of files, something containing:
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
ls -AF1 | grep -v /$ | grep -v $1 | xargs rm
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
allows "xargs" to collect as many files as it can on a command
line, and invoke "rm" repeatedly.
</BLOCKQUOTE>
<BLOCKQUOTE>
It would be prudent to try the thing out in a directory containing
only expendable files with names similar to the intended victims/saved.
</BLOCKQUOTE>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Ben]
Possibly a good idea for some systems. I've just tried it on a directory
with 1,000 files in it (created just for the purpose) and deleted 990 of
them in one shot, then recreated them and deleted only 9 of them.
Everything worked fine, but testing is indeed a prudent thing to do.
</BLOCKQUOTE>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Dan]
Or with some typists. I've more than once had to resort to backups
due to a slip of the fingers (the brain?) with an "rm" expression.
</BLOCKQUOTE>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Ben]
<*snort*> Never happened to <EM>me</EM>. No sir. Uh-uh.
<Anxious glance to make sure the weekly backup disk is where it should be>
</BLOCKQUOTE>
<BLOCKQUOTE>
I just put in that "to be deleted" display for, umm, practice. Yeah.
</BLOCKQUOTE>
<BLOCKQUOTE>
<LOL> Good point, Dan.
</BLOCKQUOTE>
<hr width="40%" align="center">
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
Thanks a million! It worked.
</STRONG></P>
<P><STRONG>
I have another question: My shell script is in a file called hw1d.sh. When I
run sh hw1d.sh, the output shows on the screen. But the command details
won't show. Is there a way I can capture the detailed command lines and
output at the same time?
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Ben]
For one thing, you shouldn't be running your script as "sh ..."; simply
make it executable via "chmod +x <scriptname>" and run it. Other than
that (I <EM>think</EM> I understand what you're asking here), you can add "-v"
to the hashbang line so it looks like this -
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
#!/bin/bash -v
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
This will print out each line as it is read.
</BLOCKQUOTE>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Mike]
Or -x, which is what I use. They do slightly different things.
Consider this program.
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
<BR>#!/bin/bash -v
<BR>TOWHOM="world"
<BR>echo "Hello"
<BR>echo $TOWHOM
<BR># This is a comment.
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
Now running it:
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
<BR>$ ./hello.sh
<BR>#!/bin/bash -v
<BR>TOWHOM="world"
<BR>echo "Hello"
<BR>Hello
<BR>echo $TOWHOM
<BR>world
<BR># This is a comment.
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
Now change -v to -x and run it.
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><pre>
$ ./hello.sh
+ TOWHOM=world
+ echo Hello
Hello
+ echo world
world
</pre></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
The variable was expanded, there's a "+ " before each program line, and
the comments are omitted. It looks like -v shows the commands <EM>before</EM>
they're interpreted and -x shows them <EM>after</EM>.
</BLOCKQUOTE>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Ben] For more details on shell scripting, see my
"Introduction to Shell Scripting" articles in LG53-57 and 59.
</BLOCKQUOTE>
<p><em>He got the issue numbers wrong, but no sense worrying about that,
here they are. -- Heather</em></p>
<ul><li><a href="../../issue52/okopnik2.html">52 - The Basics</a>
<li><a href="../../issue53/okopnik.html">53 - loops, conditions, good practices</a>
<li><a href="../../issue54/okopnik.html">54 - handy external tools</a>
<li><a href="../../issue55/okopnik.html">55 - deep, dark secrets</a>
<li><a href="../../issue57/okopnik.html">57 - color!</a>
<li><a href="../../issue58/okopnik.html">58 - cleanup and debugging tricks</a> (last in series)
</ul>
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
Thanks!
</STRONG></P>
<P><STRONG>
For practice purpose, I create file -cfile and try to rename it to cfile. I
figured out one way:
</STRONG></P>
<pre><strong> >cat <\-cfile >cfile
</strong></pre>
<P><STRONG>
But I just couldn't delete the old file -cfile because shell always
interprets as option. Is there a way I can do this?
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Dan]
Yes.
</blockquote>
<pre><blockquote>rm -- -cfile
</blockquote></pre>
<blockquote>
From "man rm":
</blockquote>
<pre><blockquote>GNU STANDARD OPTIONS
[ ... ]
-- Terminate option list.
</blockquote></pre>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Ben]
Given that "there's more than one way to do it",
</BLOCKQUOTE>
<blockquote><pre>rm ./-cfile
</pre></blockquote>
<BLOCKQUOTE>
also works. As you have found out, it's not a good idea to create
filenames with non-alphanumeric characters at the beginning: just because
you <EM>can</EM>, really does not mean that you <EM>should</EM>...
</BLOCKQUOTE>
<!-- end 3 -->
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