ch15.htm

《Perl 5 Unreleased》

postmaster           14
<BR>
ppp&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;504
<BR>
root&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0
<BR>
shutdown&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6
<BR>
sync&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5
<BR>
tparker&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;503
<BR>
uucp&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;10
<BR>
uzma&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;505
<BR>
walter&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;502</FONT></TT>
</BLOCKQUOTE>
<P>
Two sister functions exist for getting the same nine-item list
about a user in the <TT><FONT FACE="Courier">/etc/passwd</FONT></TT>
file: <TT><FONT FACE="Courier">getpwnam()</FONT></TT> and <TT><FONT FACE="Courier">getpwuid()</FONT></TT>.
The items in the returned list are in the same type as those returned
by a call to <TT><FONT FACE="Courier">getpwent()</FONT></TT>.
The <TT><FONT FACE="Courier">getpwnam()</FONT></TT> function returns
the list given a user name, whereas the <TT><FONT FACE="Courier">getpwuid()</FONT></TT>
function returns the list given a user ID.
<P>
The <TT><FONT FACE="Courier">getpwnam()</FONT></TT> and <TT><FONT FACE="Courier">getpwuid()</FONT></TT>
functions have the following syntax:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">(<I>$username, $password, $userid, $groupid,
<BR>
$quota, $comment, $userInfo, $userHome, $loginShell</I>)<BR>
</FONT></TT>&nbsp;&nbsp;&nbsp;&nbsp;<TT><FONT FACE="Courier">=
getpwnam ($name);<BR>
<BR>
<I>($username, $password, $userid, $groupid,<BR>
$quota, $comment, $userInfo, $userHome, $loginShell)<BR>
</I></FONT></TT>&nbsp;&nbsp;&nbsp;&nbsp;<TT><FONT FACE="Courier">=
getpwuid ($id);</FONT></TT>
</BLOCKQUOTE>
<P>
An empty list is returned if no matching entry is found in <TT><FONT FACE="Courier">/etc/passwd</FONT></TT>.
A common use for <TT><FONT FACE="Courier">getpwnam</FONT></TT>
is to get a user ID for a user in a Perl script and use that value
for creating temporary files.
<H3><A NAME="GettingGroupRelatedInformationwithg">Getting Group-Related
Information with <TT><FONT SIZE=4 FACE="Courier">getgrent()</FONT></TT><FONT SIZE=4>
and </FONT><TT><FONT SIZE=4 FACE="Courier">getgrnam()</FONT></TT></A>
</H3>
<P>
The <TT><FONT FACE="Courier">getgrent</FONT></TT> function is
used to list the contents of an entry in the <TT><FONT FACE="Courier">/etc/group</FONT></TT>
file. The following information is provided for each entry:
<UL>
<LI><FONT COLOR=#000000>The user group name</FONT>
<LI><FONT COLOR=#000000>The user group password, if any</FONT>
<LI><FONT COLOR=#000000>The group ID</FONT>
<LI><FONT COLOR=#000000>A list of the user IDs in this group</FONT>
</UL>
<P>
Here's the syntax for the <TT><FONT FACE="Courier">getgrent</FONT></TT>
function:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">($gname, $gpasswd, $gid, $gmembers) =
getgrent;</FONT></TT>
</BLOCKQUOTE>
<P>
This function returns four items corresponding to the previous
list. The name, password, and ID fields are all scalar values.
The value of <TT><FONT FACE="Courier">gmembers</FONT></TT> is
a list of user IDs separated by spaces.
<P>
The <TT><FONT FACE="Courier">setgrent</FONT></TT> function sets
the pointer in the <TT><FONT FACE="Courier">/etc/group</FONT></TT>
file back to the top. After <TT><FONT FACE="Courier">setgrent</FONT></TT>
is called, the next call to <TT><FONT FACE="Courier">getgrent</FONT></TT>
retrieves the first element of the <TT><FONT FACE="Courier">/etc/group</FONT></TT>
file. The <TT><FONT FACE="Courier">endgrent</FONT></TT> function
stops further access to the elements in the <TT><FONT FACE="Courier">/etc/group</FONT></TT>
file and frees up the memory used to store group information.
<P>
Here's the syntax for these functions:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">setgrent();<BR>
endgrent();</FONT></TT>
</BLOCKQUOTE>
<P>
Each call to <TT><FONT FACE="Courier">getgrent</FONT></TT> returns
one line from the <TT><FONT FACE="Courier">/etc/group</FONT></TT>
file. A <TT><FONT FACE="Courier">NULL</FONT></TT> value (that
is, an empty list) is returned when the last item is read. To
print the contents of the group file, use a <TT><FONT FACE="Courier">while</FONT></TT>
loop like the one shown in Listing 15.2.
<HR>
<BLOCKQUOTE>
<B>Listing 15.2. Getting group information.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier">1 while (($gname, $gpasswd, $gid, $gmembers)
= getgrent) {<BR>
2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;$groupsFound{$gname}
= $gmembers;<BR>
3 }<BR>
4 foreach $i (sort keys (%groupsFound)) {<BR>
5&nbsp;&nbsp;&nbsp;&nbsp; print &quot;\n User IDs for group:&quot;,
$groupsFound{$i} ;<BR>
6 }</FONT></TT>
</BLOCKQUOTE>
<HR>
<P>
The <TT><FONT FACE="Courier">getgrnam</FONT></TT> function returns
an <TT><FONT FACE="Courier">/etc/group</FONT></TT> file entry
when given a group name. Here's the syntax for the <TT><FONT FACE="Courier">getgrnam</FONT></TT>
function:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">($gname, $gpasswd, $gid, $gmembers) =
getgrnam ($name);</FONT></TT>
</BLOCKQUOTE>
<P>
The variable <TT><FONT FACE="Courier">$gname</FONT></TT> is the
group name to search for. The <TT><FONT FACE="Courier">$getgrnam</FONT></TT>
returns the same four-element list that <TT><FONT FACE="Courier">getgrent</FONT></TT>
returns. Here is the output:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">adm&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4
<BR>
bin&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1
<BR>
daemon&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2
<BR>
disk&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6
<BR>
floppy&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;11
<BR>
kmem&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;9
<BR>
lp&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;7
<BR>
mail&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;12
<BR>
man&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;15
<BR>
mem&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8
<BR>
news&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;13
<BR>
nogroup&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;65535
<BR>
root&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0
<BR>
sys&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3
<BR>
tty&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5
<BR>
users&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;100
<BR>
uucp&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14
<BR>
wheel&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;10</FONT></TT>
</BLOCKQUOTE>
<HR>
<P>
Here's another sample of how to list users given a group name.
Listing 15.3 shows a simple script that prints the users in a
group.
<HR>
<BLOCKQUOTE>
<B>Listing 15.3. A program that uses </B><TT><B><FONT FACE="Courier">getgrnam</FONT></B></TT><B>.
<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT><FONT FACE="Courier">&nbsp;1 #!/usr/bin/perl<BR>
&nbsp;2 print (&quot;Please enter name of the group:\n&quot;);
<BR>
&nbsp;3 $name = &lt;STDIN&gt;;
<BR>
&nbsp;4 chop($name); #<BR>
&nbsp;5<BR>
&nbsp;6 if (!(($gname, $gpasswd, $gid, $gmembers) = getgrnam ($name)))
{<BR>
&nbsp;7&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;die
(&quot;There is no&nbsp;&nbsp;$name group!. \n&quot;);<BR>
&nbsp;8 }<BR>
&nbsp;9<BR>
10 $count = 0;<BR>
11 while (1) {<BR>
12&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;last if
($gmembers eq &quot;&quot;);<BR>
13&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;($uid,
$gmembers) = split (/\s+/, $gmembers, 2);<BR>
14&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf
(&quot;&nbsp;&nbsp;%-15s&quot;, $uid);<BR>
15&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;$count++;
<BR>
16&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (($count
% 3) == 0) {<BR>
17&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
print (&quot;\n&quot;);<BR>
18&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
19 }<BR>
20 if ($count % 4) {&nbsp;&nbsp;&nbsp;# finish it off.<BR>
21&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;print
(&quot;\n&quot;);<BR>
22 }</FONT></TT>
</BLOCKQUOTE>
<HR>
<P>
Lines 16 and 20 print the output four items per line. <TT><FONT FACE="Courier">getgrid()</FONT></TT>
retrieves the user information as returned by <TT><FONT FACE="Courier">getgrnam()</FONT></TT>,
except that it retrieves it by group ID. Here's the syntax for
the <TT><FONT FACE="Courier">getgrid</FONT></TT> function:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">($gname, $gpasswd, $gid, $gmembers) =
getgrid ($gid);</FONT></TT>
</BLOCKQUOTE>
<P>
Generally, the call is just used to get the group name given a
group ID:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">($gname) = getgrid (3);</FONT></TT>
</BLOCKQUOTE>
<P>
Be careful, though, to parenthesize the <TT><FONT FACE="Courier">$gname</FONT></TT>
variable to indicate that the <TT><FONT FACE="Courier">$gname</FONT></TT>
variable is an element in a list and not a list itself<FONT SIZE=1>&nbsp;</FONT>!
If you make the call like this:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">$gname = getgrid (3);</FONT></TT>
</BLOCKQUOTE>
<P>
the value of <TT><FONT FACE="Courier">$gname</FONT></TT> is the
returned list, not the first element of the array.
<H2><A NAME="GettingInformationinNetworkFiles"><FONT SIZE=5 COLOR=#FF0000>Getting
Information in Network Files</FONT></A></H2>
<P>
Perl offers several functions to get information about networking
files and items in the files on your system. By using these functions,
you can create very powerful networking applications.
<H3><A NAME="ThegetnetentFunction">The <TT><FONT SIZE=4 FACE="Courier">getnetent</FONT></TT><FONT SIZE=4>
Function</FONT></A></H3>
<P>
The <TT><FONT FACE="Courier">getnetent</FONT></TT> function enables
you to read entries in the <TT><FONT FACE="Courier">/etc/networks</FONT></TT>
file for all the names and addresses recognized as valid names
by the domain name server for your machine. Here's the syntax
for <TT><FONT FACE="Courier">getnetent()</FONT></TT>:
<BLOCKQUOTE>
<TT><FONT FACE="Courier">($name, $aliases, $addrType, $inet) =
getnetent();</FONT></TT>
</BLOCKQUOTE>
<P>
Four items are returned by this function:
<UL>
<LI><FONT COLOR=#000000>The </FONT><TT><FONT FACE="Courier">$name</FONT></TT>
variable is the name of a network.
<LI><FONT COLOR=#000000>The </FONT><TT><FONT FACE="Courier">$aliases</FONT></TT>