unx28.htm

Unix Unleashed, Third Edition is written with the power user and system administrator in mind. This

<LI>vi your first chapter. Then from within vi, escape to the shell and invoke ispell with :!ispell.

<BR>

<BR></LI></UL>

<P>Although some people prefer ispell, unadorned, ordinary spell is more useful if you want to create personal or specialized dictionaries or if you want make global changes to your input file.

<BR></P>

<H4 ALIGN="CENTER">

<CENTER><A ID="I9" NAME="I9">

<FONT SIZE=3><B><I>/dev/null</I></B><B>: The Path to UNIX Limbo</B>

<BR></FONT></A></CENTER></H4>

<P>As you're surely tired of hearing, UNIX views everything as a file, including devices (such as your terminal or the printer you use). Device files are stored neatly in the /dev directory.

<BR></P>

<P>Occasionally, you specify devices by their filenames (for example, when you're reading a tape or mounting a disk drive), but most often you don't bother to think about device files.

<BR></P>

<P>There's one device file, however, that you may want to use: /dev/null.

<BR></P>

<P>The null file in the /dev directory is just what it sounds like: nothing. It's the equivalent of the fifth dimension or the incinerator chute. If you send something there, you can't get it back&#151;ever.

<BR></P>

<P>Why would you want to send output to /dev/null? If you've just created a complex table (or picture, graph, or equation), you can process your creation without wasting paper. Just direct the output to /dev/null:

<BR></P>

<PRE>tbl filename&gt; /dev/null

eqn filename&gt; /dev/null

pic filename &gt; /dev/null</PRE>

<P>You'll see any error messages on your screen. This is usually more reliable than checkeq. And you can use it for text files.

<BR></P>

<H3 ALIGN="CENTER">

<CENTER><A ID="I10" NAME="I10">

<FONT SIZE=4><B>Countoing Words with </B><B><I>wc</I></B>

<BR></FONT></A></CENTER></H3>

<P>Sometimes you need to count the words in a document. UNIX has the tool for you. The wc shell command counts lines, words, and characters. It can give you a total if you specify more than one file as input.

<BR></P>

<P>To count the words in ch01, enter wc -w ch01.

<BR></P>

<P>You can count lines by using the -l option, or characters by using the -c option. Bear in mind, however, that wc counts all your macros as words. (Refer to Chapter 6 for more details on wc.)

<BR></P>

<H3 ALIGN="CENTER">

<CENTER><A ID="I11" NAME="I11">

<FONT SIZE=4><B>Using </B><B><I>grep</I></B>

<BR></FONT></A></CENTER></H3>

<P>The grep command is an invaluable aid to writers. It is used primarily for checking the organization of a file or collection of files, and for finding occurrences of a character string.

<BR></P>

<H4 ALIGN="CENTER">

<CENTER><A ID="I12" NAME="I12">

<FONT SIZE=3><B>Checking the Organization of a Document</B>

<BR></FONT></A></CENTER></H4>

<P>If you're writing a long, complex document&#151;especially one that uses three or more levels of headings&#151;you can make sure that your heading levels are correct and also produce a rough outline of your document at the same time.

<BR></P>

<HR ALIGN=CENTER>

<NOTE>

<IMG SRC="note.gif" WIDTH = 35 HEIGHT = 35><B>NOTE:</B> This technique is useful only if you are using a macro package&#151;a reasonable assumption for a long, complex document. If you've formatted your document with embedded troff commands, this technique 

won't work.

<BR></NOTE>

<HR ALIGN=CENTER>

<P>For example, if your heading macros take the form

<BR></P>

<PRE>.H n &quot;heading&quot;</PRE>

<P>a first-level heading might be

<BR></P>

<PRE>H 1 &quot;Introduction to the XYZZY System&quot;</PRE>

<P>If your chapters are named ch01, ch02, and so on through chn, the following command will search all your chapter files for all instances of the .H macros. It will also print the filename and the line that contains the .H macro in a file called outline.

<BR></P>

<PRE>$ grep &quot;\.H &quot; ch* &gt; outline</PRE>

<P>The backslash is needed to escape the special meaning of the period. The space after H is needed so that you don't inadvertently include another macro or macros with names such as .HK or .HA. The quotation marks are used to include that space.

<BR></P>

<P>You can view your outline file with vi, or you can print it. At a glance, you're able to see whether you've mislabeled a heading in Chapter 1, omitted a third-level heading in Chapter 4, and so forth. You also have an outline of your entire document. Of 

course, you can edit the outline file to produce a more polished version.

<BR></P>

<H4 ALIGN="CENTER">

<CENTER><A ID="I13" NAME="I13">

<FONT SIZE=3><B>Finding Character Strings</B>

<BR></FONT></A></CENTER></H4>

<P>If you've just finished a 1,000-page novel and suddenly decide&#151;or are told by your editor&#151;to change a minor character's name from Pansy to Scarlett, you might vi every one of your 63 files, search for Pansy, and change it to Scarlett. But 
Scarlett isn't in every chapter&#151;unless you've written Scarlett II. So why aggravate yourself by viing 63 files when you need to vi only six? grep can help you.

<BR></P>

<P>To use grep to find out which files contain the string Pansy, enter the following:

<BR></P>

<PRE>$ grep &quot;Pansy&quot; ch* &gt; pansylist</PRE>

<P>Here, the quotation marks aren't strictly necessary, but it's a good idea to get into the habit of using them. In other situations, such as the previous example, you need them.

<BR></P>

<P>This command creates a file called pansylist, which looks something like this:

<BR></P>

<PRE>ch01:no longer sure that Pansy was

ch01:said Pansy.

ch07:wouldn't dream of wearing the same color as Pansy O'Hara.

ch43:Pansy's dead. Pansy O'Hara is dead.

ch57:in memory of Pansy. The flowers were deep purple and yellow</PRE>

<P>Now you know which chapters have to be edited: 1, 7, 43, and 57. To change Pansy to Scarlett globally, vi one of the files that contains the string Pansy and enter the following command. Make sure that you're in Command mode, not Insert mode.

<BR></P>

<PRE>:/,$ s/Pansy/Scarlett/g</PRE>

<P>The g at the end of this code line is important. If the string Pansy occurs more than once in a line, as it does in Chapter 43, g ensures that all instances be changed to Scarlett.

<BR></P>

<HR ALIGN=CENTER>

<NOTE>

<IMG SRC="note.gif" WIDTH = 35 HEIGHT = 35><B>NOTE:</B> The same cautions about making global changes apply here. You might be referring to the flower, not the character; therefore, you'll want to retain Pansy. grep usually gives you enough context to 
alert you to potential problems.

<BR></NOTE>

<HR ALIGN=CENTER>

<H3 ALIGN="CENTER">

<CENTER><A ID="I14" NAME="I14">

<FONT SIZE=4><B>Using </B><B><I>sed</I></B>

<BR></FONT></A></CENTER></H3>

<P>The UNIX stream editor, sed, provides another method of making global changes to one or more files. sed is described in Chapter 7, &quot;Editing Text Files.&quot;

<BR></P>

<HR ALIGN=CENTER>

<NOTE>

<IMG SRC="caution.gif" WIDTH = 37 HEIGHT = 35><B>CAUTION:</B> Don't use sed unless you understand the perils of overwriting your original file with an empty file.

<BR></NOTE>

<HR ALIGN=CENTER>

<P>There are two ways to use sed: on the command line or with a sed script. (The example given here uses the command line form, not because it is preferable, but because it is easier to see what is going on.) The script, called substitute, changes all 
occurrences of the first argument to the second argument. You wouldn't want to go to all this trouble just to change Pansy to Scarlett. However, because you can specify more than one command with sed&#151;in the command line form and in the sed script 
form&#151;sed is a useful and powerful tool. 

<BR></P>

<H3 ALIGN="CENTER">

<CENTER><A ID="I15" NAME="I15">

<FONT SIZE=4><B>Using </B><B><I>diffmk</I></B>

<BR></FONT></A></CENTER></H3>

<P>diffmk comes from the many diff commands offered by the UNIX system. Its purpose is to diffmark text&#151;that is, to mark text that has changed from one version of a file to another. The text is marked with a vertical bar in the right margin. 
Sometimes, other characters creep in, especially with tables.

<BR></P>

<P>Use diffmk like this:

<BR></P>

<PRE>$ diffmk oldfile newfile difffile</PRE>

<P>The order is important. If you get it wrong, diffmk blithely prints your old file with diffmarks on it. That's probably not what you want.

<BR></P>

<P>Often your files are in two different directories&#151;possibly because the files have the same names. Suppose that you have a ch01 in the draft2 directory and in the draft3 directory. You can specify a pathname for diffmk, and you can even write the 
diffmarked files into a third directory. The third directory must already exist; diffmk won't create it for you. The following command diffmarks files in two directories and writes them into a third directory. It assumes that your current directory is 
draft3.

<BR></P>

<PRE>$ diffmk ../draft2/file1 file1 ../diffdir/dfile1</PRE>

<P>If you have many chapters, you might want to consider a shell script. To create a shell script that diffmarks all the files in the draft3 directory against the files in the draft2 directory, follow these steps:

<BR></P>

<OL>

<LI>Make sure that you're in the draft3 directory&#151;that is, the directory for the new file.

<BR>

<BR></LI>

<LI>List the files in draft3:

<BR>

<BR><B>$ ls &gt; difflist</B>

<BR>

<BR></LI>

<LI> <B>3.</B> Create the following shell script:

<BR>

<BR>for i in 'cat difflist'

<BR>do

<BR>diffmk ../draft2/$i $i ../diffdir/d$i

<BR>done

<BR>

<BR></LI>

<LI> <B>4.</B> Make the script executable:

<BR>

<BR><B>$ chmod +x diffscript</B>

<BR>

<BR></LI>

<LI> <B>5.</B> Put diffscript in your bin:

<BR>

<BR><B>$ mv diffscript $HOME/bin</B>

<BR>

<BR></LI>

<LI> <B>6.</B> Execute diffscript:

<BR>

<BR><B>$ diffscript</B>

<BR></LI></OL>

<H3 ALIGN="CENTER">

<CENTER><A ID="I16" NAME="I16">

<FONT SIZE=4><B>The </B><B><I>man</I></B><B> Command</B>

<BR></FONT></A></CENTER></H3>

<P>The man command consults a database of stored UNIX system commands&#151;basically everything that is in the system reference manuals&#151;and nroffs it to your screen. If you don't have all that documentation on a shelf in your office, the man command 
can save the day.

<BR></P>

<P>man is simple to use:

<BR></P>

<PRE>man commandname</PRE>

<P>The output is far from beautiful, and it's slow. It's paged to your screen, so you press Enter when you're ready to go on to the next page. You can't backtrack, though. Once you leave the first screen&#151;that is, the one with the command syntax on 
it&#151;the only way you can see it again is to run the man command a second time.

<BR></P>

<P>If your terminal has windowing or layering capabilities, man can is more useful, because you can look at it and type on your command line at the same time.

<BR></P>

<P>You can also print the output from man, but you may not know which printer the output is going to. If you work in a multi-printer environment, this can be a nuisance. Check with your system administrator.

<BR></P>

<H3 ALIGN="CENTER">

<CENTER><A ID="I17" NAME="I17">

<FONT SIZE=4><B>Using SCCS to Control Documentation</B>

<BR></FONT></A></CENTER></H3>

<P>Although the Source Code Control System&#151;SCCS for short&#151;was written to keep track of program code, it also makes a good archiving tool for documentation. It saves each version of a text file&#151;code, troff input, and so on&#151;and 
essentially enables only the owner to change the contents of the file. SCCS is described in detail in Chapter 30, &quot;SCCS Version Control.&quot; You can use SCCS to control versions of a document that you often revise. You can also use SCCS on drafts of 

a document. If you work with a publications group and your group doesn't have a good archiving and document control system, look into SCCS.

<BR></P>

<P><A HREF="unx27.htm"><IMG SRC="bluprev.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="Previous Page"></A>

<A HREF="index.htm"><IMG SRC="blutoc.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="TOC"></A>

<A HREF="unx29.htm"><IMG SRC="blunext.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="Next Page"></A>

<A HREF="index.htm"><IMG SRC="bluprev.gif" WIDTH = 32 HEIGHT = 32 BORDER = 0 ALT="Home"></A>

</P></BODY></HTML>