Because MH stores messages in UNIX files, it can take advantage of UNIX links, introduced here. They let you have more than one name for the same file. The following list presents an overview of using links:
Remember that MH makes standard ("hard") links, not symbolic ("soft") links. If you need to link between filesystems, see the Section Using Symbolic Links.
To find out whether two messages are linked, first scan them both. The format file called scan.size will show the number of characters in each message (for more information see the Section scan Format Files):
% scan -form scan.size 13 +reports 13 12/14 892 Vicki Thomas Progress Report<<I'm out o % scan -form scan.size 22 +vicki 22 12/14 892 Vicki Thomas Progress Report<<I'm out oThe messages look identical: each one has 892 characters. But to be sure that the messages are linked (and not just identical copies), compare the files' i-numbers. (To be completely sure, you need to compare the device names, too. But it's very unlikely that two message files which scan the same and have the same i-numbers would not be linked.) (You may also want to read the Section Technical Stuff About Links.) To compare the i-numbers, list the two message files with ls -li. Be sure to use backquotes (`), not single quotes ('). Fill in the message number and folder name:
% ls -li `mhpath 13 +reports` 20930 -rw------- 1 eds 892 Feb 1 04:32 /u1/eds/Mail/reports/13 % ls -li `mhpath 22 +vicki` 2508 -rw------- 2 eds 892 Dec 14 17:31 /u1/eds/Mail/vicki/22The first number in the ls -li output is the i-number of the file (your version of ls might be different -- if you aren't sure, ask a local expert). These two files have different i-numbers (20930 and 2508), so they are not linked. The third item in each line is the link count -- it tells how many links that file has. Here, the first file has one link (itself) and the second has two. If the files were linked, both link counts would be the same.
If you want to replace the "non-linked" message in the reports folder with a link to the message in the vicki folder, here's how:
% rmm +reports 13
% refile -link +reports -src +vicki 22That might be easier to see in two steps:
% folder +vicki vicki+ has 32 messages ( 1- 32); cur= 4. % refile -link 22 +reports
Have you ever asked yourself, "What folder did I put that message in?" You can use pick and a loop to search lots of folders, as in Section Searching More Than One Folder. This section explains a setup you might like better: a link folder. (That's not official MH terminology. I made up the name.)
When you want to save a message, you can link the message into two folders: the folder where you'd usually store it, and a special folder that has links to all (or many of) your messages. Because the link doesn't take any more disk space, why not do it? The refile command can link messages into more than one folder. See the Section Moving and Linking Messages: refile.
To find a message, search the link folder.
One Folder, Many Folders, Subfolders...
There are a lot of ways to set up a link folder, depending on your mail configuration and your wants. Find something that's simple enough to manage but capable enough to help you find your messages. Some ideas to get you started:
If you have MH 6.7 or later, a very handy trick is to link a message into several folders -- and sort those folders different ways. For example, link a message into folders named date, from, and subject. Use the commands sortm, sortm -textfield from, and sortm -textfield subject, respectively.
Making the Links
To refile a message into your recipes folder with a link to the link folder a, type:
% refile +recipes +aIn some cases, instead of using a top-level a folder, I make a separate a subfolder with a name like mh-book/a:
% refile +mh-book/a +mh-book/revisions +mh-book/readersIf you use the C shell, its curly-brace operators {...,...} will let you automatically repeat the top-level folder name. From the previous example:
% refile +mh-book/{a,revisions,readers} C shell
If you already have folders full of messages, you can use refile -link to link existing messages into your link folder. Use a command like:
% refile -link all +aOr, use a shell loop like the one in the Example below. In the example, I give the loop a list of a few folders; it links all of those messages into a folder called ln.
Example: Linking existing messages into new all-message folder
C shell:
% foreach f (rpts memos ...) ? refile -src +$f -link all +ln ? endBourne and Korn shells:
$ for f in rpts memos ... > do refile -src +$f -link all +ln > doneTo link all messages in all folders instead, you could replace the first line of the previous Example with the line:
% foreach f (`folders -fast | fgrep -v -x ln`)or:
$ for f in `folders -fast | fgrep -v -x ln`The command fgrep -v -x ln avoids trouble by omitting the ln folder in the list of folders to link from. Add the -recurse option to make folders include subfolders too.
Finding Stuff in a Link Folder
After making that setup, you might want to sort the link folder by date once in a while (see Section Sorting Messages: sortm). That makes it easier for pick to find messages, because the folder can get really huge. If you're looking for a message from the last month, and your a folder has a year's worth of messages, you can give pick a shorter range of messages to search. For example, if you guess that there aren't more than 100 messages from the last month, you can save a lot of time with:
% pick last:100 ...
Don't Break Links Accidentally
If you make links to many of your messages, you'll probably want to give the -inplace switch to commands that edit messages. It makes sure that annotations won't break one of your links. Do it in your MH profile for the anno command. Also, if you use -annotate with repl, forw, or dist, add -inplace there, too.
There's one gotcha about linked messages. When you want to remove the message, if you don't remove all the links, the message isn't taken off the disk. There's no MH command that does the whole job. But, with help from a couple of UNIX commands, it's a pretty easy job to do. (Reading the Chapter Key Parts of the UNIX Filesystem should help you understand the steps below.) If you do this a lot, it's worth writing a little shell script to find the links for you -- and maybe even to remove them.
Let's say you want to remove message 234 in your reports folder and its link in the a folder:
% cd `mhpath +`
% ls -i reports/234 37023 reports/234
% find a -inum 37023 -print a/1708
% rmm 234 +reports % rmm 1708 +a
% find . -inum 37023 -print ./reports/234 ./done/23 ./a/1708There, we found the link in the a folder and another link too: message 23 in the done folder.
For example, a group of software maintenance people might want to link to certain messages in certain folders on a central problem-tracking account. Each maintenance person could have a folder in his or her MH directory, with a list of messages for the problems that were assigned to him or her. When a new problem is assigned, the maintainer could make a new link. When the problem is solved, the maintainer could rmm his or her personal link to the message. The group's manager could use a command like anno -inplace to update the messages in the central problem-tracking folders, and all the maintainers would see the changes in their linked messages instantly.
In the right situation, with some planning and forethought, a system like that can be effective. Here are some things to watch out for:
% folder +/u3/jdpeek/Mail/tester /u3/jdpeek/Mail/tester+ has 5 messages ( 1- 5); cur= 4. % scan 1 04/06 mary@hahvahd.edu rcvtty -- how do I use it?<<I've 2 11/13 well!pokey@phlabs Re: Encapsulation destroying goo 3 03/09 Barbara Zimmerman Confused over mh-format files<<O scan: unable to open message 4: Permission denied, continuing... scan: unable to open message 5: Permission denied, continuing... % refile -link 2 +test % scan +test 1+ 12/14 jdpeek@rodan.acs. I'm out of town<<I'm out of town 2 01/28*To: << -- Jerry Peek; Syracuse Univers 3 02/03*To:jerryp sdaff<<dfkjdf --Jerry Peek; Syra 4 12/14 jdpeek@rodan.acs. I'm out of town<<I'm out of town 5 11/13 well!pokey@phlabs Re: Encapsulation destroying gooNotice that no matter what your current folder is, you always refer to your own folders with their normal name (like +test). You refer to other users' folders by using a full pathname with a plus sign (+) before it, like +/u3/jdpeek/Mail/tester. (But you can still use relative folder operators. For instance, let's say your current folder is /u3/jdpeek/Mail/tester. You could get to its subfolder sub with @sub as well as with +/u3/jdpeek/Mail/tester/sub. See the Section Relative Folder Names for more information.)
Also notice the Permission denied warnings. The warnings tell ehuser that jdpeek hasn't given her permission to read those two messages. The Section Sharing Other Users' Folders explains more.
As the Section Links explains, the hard links that MH uses can't cross filesystems. MH can't link to a message in a folder on another filesystem or across a network. (Not yet, at least.) Instead of bothering with the complications of links, MH (but not xmh) users can access any folder on any filesystem by typing its pathname -- see the Section Sharing Other Users' Folders.
Still need to make a link? Does your UNIX have symlinks (symbolic links, the ln -s command)? It's possible to make symlinks to folders, but that can be tricky. Symlinks will also work for individual messages. I recommend that you don't use symlinks unless you need them. Unlike hard links, each symlink takes a block of disk space. Also, because MH doesn't support them (not yet, anyway), using symlinks with MH seems like a "hack" to me... but not enough of a hack to keep me from explaining how to use them. :-)
I'll use my setup as an example. I have a workstation with a local disk that has a /mhdir directory; I store most of my mail there. But I need to share some of my mail with other people in the company. That mail is in my home directory, /u/jerry/Mail, which is part of a filesystem mounted across the network to all of our computers. On my workstation, my MH profile has Path: /mhdir in it. (On other computers, I set the MH environment variable to point to an MH profile with the other Path:. But that's not important in this example.)
Symlinks to Messages
To make a new symlink from my stuff folder on my local filesystem that points to message 822 in the bookq folder on the other filesystem:
% scan 822 +/u/jerry/Mail/bookq 822 -07/10 Jeffrey Smith Vol 8 of X Windows set<<Hi! Is Vol 8 % ln -s `mhpath 822` `mhpath new +stuff` % scan last +stuff 2 -07/10 Jeffrey Smith Vol 8 of X Windows set<<Hi! Is Vol 8 % ls -l `mhpath 2` lrwxrwxrwx 1 jerry 23 Jul 14 09:20 /mhdir/stuff/2 -> /u/jerry/Mail/bookq/822
NOTE: Don't use sortm or folder -pack on the folder where a symbolic link points (in the example above, the bookq folder). If you do, the link may end up pointing to a different message -- or no message at all.
Hard links (the kind that MH makes) don't have this problem.
If you remove or refile the message that a link points to, remember to remove the link too. Otherwise you'll see strange errors like:
% rmm 822 +/u/jerry/Mail/bookq % scan +stuff 1 01/26 To:jerry Messages to handle in inbox, bookq scan: unable to open message 2: No such file or directory, continuing...In general, you can just use rmm to remove the link. If that doesn't work, remove it with the UNIX rm command:
% rm `mhpath 2`
Symlinks to Folders
You can also make a symbolic link from your top-level MH directory to another folder in a different MH directory or vice versa.
CAUTION: If you link to folders -- especially to subfolders -- be sure you know what you're doing. If you link to a folder, and there's also a symlink from a folder underneath it pointing back to your folder, you can get an infinite loop. MH commands like folder -recurse will not catch this.
Also, be sure to remove the link with rm, not rmf. See the CAUTION at the end of this section.
The other problem you can have with symlinks to folders comes when you use folders for a summary of your folders (or, worse, in a loop run by some script to do something to all your folders). If one of the folders is a read-only folder, it can appear twice. Say I've made a symlink named project in my local MH directory that points to the read-only folder /u/barb/Mail/zeta. Unless I remember to rmf the reference to /u/barb/Mail/zeta (explained in the Section Removing Folders: rmf), the folders output will look like the next Example.
Example: Symlink causes double listing of read-only folder
Folder # of messages ( range ); cur msg ... /u/barb/Mail/zeta has 52 messages ( 1- 64). ... project has 52 messages ( 1- 64).And, of course, the relative folder operator @ won't do what you expect it to after you change your current folder through a symlink.
"Okay, okay," you say, "tell me how to do it anyway!" It's easy. Just cd to the directory above where you want the folder to appear, and then use ln -s. For instance, I'll make the link to Barb's zeta folder shown in the example above. In this case, to make the top-level "folder" (symlink), I'll need to go to the top-level MH directory:
% cd `mhpath +` % ln -s /u/barb/Mail/zeta projectThe next example shows how to make a "subfolder" (symlink) called work/zeta to Barb's zeta folder. When the symlink has the same name as what it points to, you don't need to give ln the name twice:
% cd `mhpath +work` % ln -s /u/barb/Mail/zetaIf you remove the folder that a symlink points to, remember to remove the symlink too. To remove the symlink, be sure to use the UNIX rm command, not the MH rmf command! For example, to remove a symlink named tmp, type:
% rm `mhpath +tmp`
CAUTION: Do not use the MH rmf command to remove a symbolic link to a folder. If you do (on MH 6.7.2 and 6.8.3, at least), rmf will not remove the symlink. Instead, if it can, rmf will remove all messages from the folder that the link points to! That's another reason why I think you should avoid symbolic links to folders.
[Table of Contents] [Index] [Previous: Annotating Headers with anno] [Next: Bursting Messages]
This file is from the third edition of the book MH & xmh: Email for Users & Programmers, ISBN 1-56592-093-7, by Jerry Peek. Copyright © 1991, 1992, 1995 by O'Reilly & Associates, Inc. This file is freely-available; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation. For more information, see the file copying.htm.
Suggestions are welcome: Jerry Peek <jpeek@jpeek.com>