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<P><BR></P>
<H3><A NAME="Heading16"></A><FONT COLOR="#000077">Wildcards</FONT></H3>
<P>Like UNIX (and DOS, for that matter), Linux supports wildcards in command lines and shells scripts. A <I>wildcard</I> is merely shorthand for a character or a string of characters. Wildcards can come in handy if you’re looking for a file and you’ve forgotten the specific filename (geez, I <I>know</I> the file ends in <I>1996</I>), or if you want to see a list of files that fall within specific parameters (such as ending with <I>.c</I>, useful if you plan on using Linux for software development).</P>
<P>There are three types of Linux wildcards: <B>*</B>, <B>?</B>, and [<B>...</B>]. Each will be explained.</P>
<BLOCKQUOTE>
<P><FONT SIZE="-1"><HR><B>NOTE: </B>Technically, wildcards are the province of the shell, and in theory a discussion of wildcards should take place with a discussion of shells. For our purposes, however, we’re going to discuss wildcards at this point in the Linux discussion, because what we’re saying here applies to all shells.<HR></FONT>
</BLOCKQUOTE>
<P>In the previous section covering the <B>ls</B> command, we covered the command’s use when it’s applied to single files. However, there may be times when you want to list a set of files that share a common characteristic, such as ending with <I>.c</I>. In this instance, you can tell <B>ls</B> to look for every file that ends with <I>.c</I>, using the following command line:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~$ ls *.c
aardvark.c stuff.c titles.c xylophone.c
</PRE>
<!-- END CODE SNIP //-->
<P>In this instance, <B>ls</B> is told to substitute <B>*</B> for any portion of a filename preceding an ending of <I>.c</I>. And, as you can see from the list of files, the command was successful. The <B>ls</B> is used to match any number of characters in a string, including zero characters:</P>
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<PRE>
gilbert:~$ ls titles*
titles titles.c
</PRE>
<!-- END CODE SNIP //-->
<P>In the case of <I>titles</I>, the wildcard matched zero characters.</P>
<P>The asterisk (<B>*</B>) can be used at the beginning or end of a wildcard expression. You can also use more than one asterisk in an expression:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~$ ls t*.*
titles.c
</PRE>
<!-- END CODE SNIP //-->
<P>If you wanted to list the files with the string <I>titles</I> anywhere in the filename, you could use the following command line:</P>
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<PRE>
gilbert:~$ ls *titles*
subtitles titles titles.c
</PRE>
<!-- END CODE SNIP //-->
<P>The asterisk wildcard is the most expansive wildcard available. On the other end of the spectrum is the question-mark wildcard, which is used to match a single character:
</P>
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<PRE>
gilbert:~$ ls title?
titles
</PRE>
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<P>In this instance, <B>ls</B> did not match <B>titles.c</B>, which contains <I>two</I> characters after the search string of <I>title</I>. <B>Titles</B>, meanwhile, contained only one character after the search string of <I>title</I>, which matched the parameters of the <B>ls</B> command.</P>
<P>The final wildcard is used to return specific characters, as defined by brackets (<B>[]</B>). For example, you’re looking through a directory filled with memos from the last 12 months. Since you’ve been a good Linux user, you’ve been placing a number at the end of every file, signifying the month it was written. (Yes, we know you’re not likely to have too many files if you’ve just installed Linux. Think of this advice as something you’ll need in the future.) You want to track down a memo you wrote sometime in the summer, but you can’t remember the name of the file, and a reading through the directory listings don’t spark a memory. In this instance, you’ll want to narrow down the directory listings to files ending in <I>6</I>, <I>7</I>, or <I>8</I> (corresponding to June, July, and August). To do this with the <B>ls</B> command, you’d enter <B>6</B>–<B>8</B> in brackets:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~/memos$ ls *[6-8]
golf.8 golfanne.8 golfpat.6 golfjim.6
golftod.6 golftom.7
</PRE>
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<P>This narrows down the list of files returned by <B>ls</B>. It also means you probably play too much golf.</P>
<P>In the preceding example, we asked <B>ls</B> to return files that ended with a range of characters, i.e., in <I>6</I>, <I>7</I>, or <I>8</I>. You can also use this wildcard to return a single character:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~/memos$ ls *[6]
golfpat.6 golfjim.6 golftod.6
</PRE>
<!-- END CODE SNIP //-->
<P>If you’re searching for a character (remembering, of course, that Linux distinguishes between uppercase and lowercase letters at all times) or range of characters, you can list them in the brackets:
</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~/memos$ ls report.[Ee]rc
report.Erc report.erc
</PRE>
<!-- END CODE SNIP //-->
<P>Wildcards can be used with any Linux command.
</P>
<H4 ALIGN="LEFT"><A NAME="Heading17"></A><FONT COLOR="#000077">Creating Directories with Mkdir</FONT></H4>
<P>The <B>mkdir</B> command is used to create directories. If you plan on using Linux for most of your day-to-day stuff, we advise creating directories to help organize the many files Linux (and any other version of UNIX, for that matter) creates. Using <B>mkdir</B> is simple:</P>
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<PRE>
gilbert:~$ mkdir <I>directory</I>
</PRE>
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<P>where <I>directory</I> is the name of the directory you want to create. To create a directory named <B>letters</B> in your home directory, you’d use the following command:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~$ mkdir letters
</PRE>
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<P>To see if the directory was really created, you can use the <B>ls</B> command:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~$ ls
letters/ text
</PRE>
<!-- END CODE SNIP //-->
<P>You can also use it to create a new directory elsewhere in the directory hierarchy:
</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~$ mkdir /users/kevin/letters
gilbert:~$ ls /users/kevin
letters/
</PRE>
<!-- END CODE SNIP //-->
<P><B>Mkdir</B> can create more than one directory on a command line:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~$ mkdir letters data
gilbert:~$ ls
data/ letters/ text
</PRE>
<!-- END CODE SNIP //-->
<P><B>Mkdir</B> can also create a directory and a subdirectory in a single command line:</P>
<!-- CODE SNIP //-->
<PRE>
gilbert:~$ mkdir -p /letters/eric
</PRE>
<!-- END CODE SNIP //-->
<P>Other options to <B>mkdir</B> are listed in Table 4.6.</P>
<CENTER>
<TABLE WIDTH="95%"><CAPTION><B>Table 4.6</B> Other Options to the Mkdir Command
<TR>
<TH WIDTH="30%" ALIGN="LEFT">Option
<TH WIDTH="70%" ALIGN="LEFT">Result
<TR>
<TH COLSPAN="2"><HR>
<TR>
<TD>m <I>mode</I>
<TD>Sets the mode for the new directory.
<TR>
<TD COLSPAN="2"><HR>
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