ch25.htm

this is a book on pearl , simple example with explanation is given here. it could be beneficial for

</CENTER>

<P>

<BLOCKQUOTE>

<PRE>

$answer = 3;

eval(&quot;$answer = ;&quot;);

if ($@ eq &quot;&quot;) {

    print(&quot;eval() returned success.\n&quot;);

}

else {

    print(&quot;eval() error: $@&quot;);

}

</PRE>

</BLOCKQUOTE>

<H3><A NAME="execLIST">

exec (LIST)</A></H3>

<P>

<B>Category:</B> Process<BR>

<B>Return Value:</B> None.<BR>

<B>Definition:</B> This fuNCtion passes control from the script

to an external system command. <B>There is no return from this

call.</B> Note that <TT>system()</TT>

calls external commands and does return.

<BLOCKQUOTE>

<PRE>

exec(&quot;cat /etc/motd&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="existsEXPR">

exists (EXPR)</A></H3>

<P>

<B>Category:</B> Hash<BR>

<B>Return Value:</B> SCALAR, true if <TT>EXPR</TT>

is an entry in a hash, false if not.<BR>

<B>Definition:</B> Tests whether a given key value exists in an

associative array.

<BLOCKQUOTE>

<PRE>

%test = ( 'One' =&gt; '1', 'Two' =&gt; '2');

if (exists($test{'One'})) {

    print(&quot;exists() returned success.\n&quot;);

}

else {

    print(&quot;exists() returned an error.\n&quot;);

}

</PRE>

</BLOCKQUOTE>

<H3><A NAME="exitEXPR">

exit ([EXPR])</A></H3>

<P>

<B>Category:</B> Process<BR>

<B>Return Value:</B> None.<BR>

<B>Definition:</B> Evaluates <TT>EXPR</TT>

and exits the program with that value as the exit code. The default

value for the exit code is 0 if no argument is supplied. If an

<TT>END</TT> block <BR>

has been defined, it will be called. Also, object destructors

may be called before the process truly ends.

<BLOCKQUOTE>

<PRE>

exit(16);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="expEXPR">

exp ([EXPR])</A></H3>

<P>

<B>Category:</B> Math<BR>

<B>Return Value:</B> SCALAR, the natural log base (e) to the power

of <TT>EXPR</TT>.<BR>

<B>Definition:</B> Returns the natural log base (e) to the power

of <TT>EXPR</TT>. If no parameter

is specified, <TT>$_</TT> is used.

<BLOCKQUOTE>

<PRE>

print &quot;exp() e**1 is &quot;, exp(1), &quot;\n&quot;;

</PRE>

</BLOCKQUOTE>

<H3><A NAME="fcntlFILEHANDLEFUNCTIONPACKEDFLAGS">

fcntl (FILEHANDLE, FUNCTION, PACKED_FLAGS)</A></H3>

<P>

<B>Category:</B> File, UNIX<BR>

<B>Return Value:</B> None.<BR>

<B>Definition:</B> In Perl 5 use the <TT>fntcl</TT>

module. In Perl 4 there should be some mechanism for linking the

perl fuNCtions to the system fuNCtions which is usually executed

when Perl is installed. See the <TT>perlfuNC</TT>

man page for more information.

<H3><A NAME="filenoFILEHANDLE">

fileno (FILEHANDLE)</A></H3>

<P>

<B>Category:</B> File<BR>

<B>Return Value:</B> SCALAR, the file descriptor for <TT>FILEHANDLE</TT>.

<BR>

<B>Definition:</B> Returns the file descriptor given a file handle.

File descriptors are useful when using bitmaps for the <TT>select()</TT>

fuNCtion.

<BLOCKQUOTE>

<PRE>

print(&quot;fileno() &quot;, fileno(FILE), &quot;\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="flockFILEHANDLEOPERATIONFLAGS">

flock (FILEHANDLE, OPERATION_FLAGS)</A></H3>

<P>

<B>Category:</B> File<BR>

<B>Return Value:</B> SCALAR, true if successful, false if not.

<BR>

<B>Definition:</B> Lets you access file locks. You can place an

exclusive lock, place a shared lock, or remove locks. You can

find more information about <TT>flock()</TT>

in section 2 of the UNIX manual pages.

<H3><A NAME="fork">

fork ( )</A></H3>

<P>

<B>Category:</B> Process UNIX<BR>

<B>Return Value:</B> SCALAR, the pid of the child process or <TT>undef</TT>

is unsuccessful.<BR>

<B>Definition:</B> Starts a child process. Both child and parent

processes start executing the line of code immediately following

the <TT>fork()</TT> call. You can

find more information about <TT>fork()</TT>

in section 2 of the UNIX manual pages.

<H3><A NAME="formlinePICTURELIST">

formline (PICTURE, LIST)</A></H3>

<P>

<B>Category:</B> Miscellaneous<BR>

<B>Return Value:</B> None.<BR>

<B>Definition:</B> This internal fuNCtion is used by the format

mechanism. It allows direct manipulation of the format process

by adding values to the format accumulator (<TT>$^A</TT>).

For more information about formats, see <A HREF="ch11.htm" >Chapter 11</A>, &quot;Creating

Reports.&quot;

<H3><A NAME="getcFILEHANDLE">

getc ([FILEHANDLE])</A></H3>

<P>

<B>Category:</B> File, Input<BR>

<B>Return Value:</B> SCALAR, the inputted character. Null if at

end of file.<BR>

<B>Definition:</B> Returns the next character <TT>FILEHANDLE</TT>

or <TT>STDIN</TT> if no filehandle

is specified.

<BLOCKQUOTE>

<PRE>

open(FILE, &quot;/etc/motd&quot;);

print &quot;getc() &quot;, getc(FILE), &quot;\n&quot;;

close(FILE);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getgrent">

getgrent ( )</A></H3>

<P>

<B>Category:</B> Group, UNIX<BR>

<B>Return Value: </B>in Scalar Context : Returns the next group

name or the undefined value if no more groups or an error occurred.

<BR>

<B>Return Value in Array Context :</B> (<TT>$name,

$passwd, $gid, $members</TT>) or an empty list.<BR>

<B>Definition:</B> Returns information about groups taken from

the <TT>/etc/group</TT> system file.

If called repeatedly, it will iterate through the entries in the

<TT>/etc/group</TT> file.

<BLOCKQUOTE>

<PRE>

($name, $pw, $gid, @members) = getgrent();

print(&quot;getgrent() Examines /etc/group [$name,$gid] file.\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getgrgidGID">

getgrgid (GID)</A></H3>

<P>

<B>Category:</B> Group, UNIX<BR>

<B>Return Value: </B>in Scalar Context: The next group name that

belongs to <TT>GID</TT>.

<P>

<B>Return Value in Array Context:</B> (<TT>$name,

$passwd, $gid, $members</TT>) or an empty list.<BR>

<B>Definition:</B> Returns information about groups taken from

the <TT>/etc/group</TT> system file.

<BLOCKQUOTE>

<PRE>

($grname, $grpw, $gid, @members) = getgrgid(0);

print(&quot;getgrgid() Returns group name given GID [$grname]\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getgrnameNAME">

getgrname (NAME)</A></H3>

<P>

<B>Category:</B> Group, UNIX<BR>

<B>Return Value: </B>in Scalar Context: The next group id that

belongs to <TT>NAME</TT>.<BR>

<B>Return Value in Array Context:</B> (<TT>$name,

$passwd, $gid, $members</TT>) or an empty list.<BR>

<B>Definition:</B> Returns information about groups taken from

the <TT>/etc/group</TT> system file.

<BLOCKQUOTE>

<PRE>

($grname, $grpw, $gid, @members) = getgrnam(&quot;root&quot;);

print(&quot;getgrnam() Returns group GID given name [$gid]\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="gethostbyaddrADDRESSAFINIT">

gethostbyaddr (ADDRESS, AF_INIT)</A></H3>

<P>

<B>Category:</B> Host, Socket<BR>

<B>Return Value: </B>in Scalar Context: Name of host addressed

by <TT>ADDRESS</TT> or undefined if

the host could not be found.<BR>

<B>Return Value in Array Context:</B> (<TT>$name</TT>,

<TT>$aliases</TT>, <TT>$addrtype</TT>,

<TT>$length</TT>, <TT>@addrs</TT>)

or an empty list.<BR>

<B>Definition:</B> Looks in the <TT>/etc/hosts</TT>

system file or checks a Domain Name Server for a server with <TT>ADDRESS</TT>.

The value for <TT>AF_INIT</TT> is

always 2.

<BLOCKQUOTE>

<PRE>

use Socket;

$addr = pack('C4', (140,203,7,103));

($name, $alias, $addrtype, $length, @addrs) = gethostbyaddr($addr, AF_INET);

print(&quot;gethostbyaddr() [$alias].\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="gethostbynameNAMEPROTOCOL">

gethostbyname (NAME, [PROTOCOL])</A></H3>

<P>

<B>Category:</B> Host, Socket<BR>

<B>Return Value: </B>in Scalar Context: Address of the host called

<TT>NAME</TT> or undefined if the

host could not be found.<BR>

<B>Return Value in Array Context:</B> (<TT>$name,

$aliases, $addrtype, $length, @addrs</TT>) or an empty

list.<BR>

<B>Definition:</B> Looks in the <TT>/etc/hosts</TT>

system file or checks a Domain Name Server for a server called

<TT>NAME</TT>.

<BLOCKQUOTE>

<PRE>

($name, $alias, $addrtype, $length, @addrs) = gethostbyname(&quot;lyNCh&quot;);

print(&quot;gethostbyname() [$alias].\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="gethostent">

gethostent ( )</A></H3>

<P>

<B>Category:</B> Host, UNIX<BR>

<B>Return Value: </B>in Scalar Context: Name of the next host

in <TT>/etc/hosts</TT>. or the undefined

value.<BR>

<B>Return Value in Array Context:</B> (<TT>$name</TT>,

<TT>$aliases</TT>, <TT>$addrtype</TT>,

<TT>$length</TT>, <TT>@addrs</TT>)

or an empty list.<BR>

<B>Definition:</B> Looks in the <TT>/etc/hosts</TT>

system file.

<BLOCKQUOTE>

<PRE>

($name, $alias, $addrtype, $length, @addrs) = gethostent();

print(&quot;gethostent() [$alias].\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getlogin">

getlogin ( )</A></H3>

<P>

<B>Category:</B> Process, UNIX<BR>

<B>Return Value:</B> SCALAR, the name of the current login.<BR>

<B>Definition:</B> Gets the current login name from the <TT>/etc/utmp</TT>

system file. Use <TT>getpwuid()</TT>for

more information on the login because the information stored in

<TT>/etc/utmp</TT> is limited.

<BLOCKQUOTE>

<PRE>

print (&quot;getlogin() &quot;, getlogin(), &quot;\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getnetbyaddrADDRESSADDRTYPE">

getnetbyaddr (ADDRESS, ADDR_TYPE)</A></H3>

<P>

<B>Category:</B> Network<BR>

<B>Return Value: </B>in Scalar Context: The network name that

has an address of <TT>ADDRESS</TT>

or undefined.<BR>

<B>Return Value in Array Context:</B> (<TT>$name</TT>,

<TT>$aliases</TT>, <TT>$addrtype</TT>,

<TT>$net</TT>) or an empty list.<BR>

<B>Definition:</B> Looks for the network information in the <TT>/etc/networks</TT>

system file.

<BLOCKQUOTE>

<PRE>

($addrtype) = (getnetent())[2];

($name, $alias, $addrtype, $net) = getnetbyaddr($net, $addrtype);

print(&quot;getnetbyaddr() Reads /etc/networks [$name]\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getnetbynameNAME">

getnetbyname (NAME)</A></H3>

<P>

<B>Category:</B> Network<BR>

<B>Return Value: </B>in Scalar Context: The network address of

<TT>NAME</TT> or undefined.<BR>

<B>Return Value in Array Context:</B> (<TT>$name</TT>,

<TT>$aliases</TT>, <TT>$addrtype</TT>,

<TT>$net</TT>) or an empty list.<BR>

<B>Definition:</B> Looks for the network information in the <TT>/etc/networks</TT>

system file.

<BLOCKQUOTE>

<PRE>

($name, $alias, $addrtype, $net) = getnetbyname(&quot;localnet&quot;);

print(&quot;getnetbyname() Reads /etc/networks [$name]\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getnetent">

getnetent ( )</A></H3>

<P>

<B>Category:</B> Network<BR>

<B>Return Value in Scalar Context:</B> The next network name in

<TT>/etc/networks</TT> or undefined.

<BR>

<B>Return Value in Array Context:</B> (<TT>$name</TT>,

<TT>$aliases</TT>, <TT>$addrtype</TT>,

<TT>$net</TT>) or an empty list.<BR>

<B>Definition:</B> When called repeatedly, it iterates over the

information in the <TT>/etc/networks</TT>

system file.

<BLOCKQUOTE>

<PRE>

($name, $alias, $addrtype, $net) = getnetent();

print(&quot;getnetent() Reads /etc/networks [$name, $addrtype]\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getpeernameSOCKET">

getpeername (SOCKET)</A></H3>

<P>

<B>Category:</B> Sockets<BR>

<B>Return Value:</B> SCALAR, the address of the remote side of

a socket connection represented by <TT>SOCKET</TT>.

<BR>

<B>Definition:</B> Gets the packed address of the remote side

of a socket. The address can then be used with the <TT>unpack()</TT>

fuNCtion to retrieve the protocol family, port and ip address

values.

<BLOCKQUOTE>

<PRE>

$sockaddr = 'S n a4 x8';

$packedRemoteAddr = getpeername(S);

($family, $port, $remoteAddr) = unpack($sockaddr,$packedRemoteAddr);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getpgrpPID">

getpgrp (PID)</A></H3>

<P>

<B>Category:</B> Groups, Process, UNIX<BR>

<B>Return Value:</B> SCALAR, the current process group for <TT>PID</TT>.

If <TT>PID</TT> is not specified or

0 is used, the current group of the current process is returned.

<BR>

<B>Definition:</B> Finds the current process group for a given

<TT>pid</TT>.

<BLOCKQUOTE>

<PRE>

print(&quot;getpgrp() &quot;, getpgrp(0), &quot;\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getppid">

getppid ( )</A></H3>

<P>

<B>Category:</B> Process, UNIX<BR>

<B>Return Value:</B> SCALAR, the pid of the parent process.<BR>

<B>Definition:</B> Finds the pid of the parent process.

<BLOCKQUOTE>

<PRE>

print(&quot;getppid() &quot;, getppid(), &quot;\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getpriorityWHICHWHO">

getpriority (WHICH, WHO)</A></H3>

<P>

<B>Category:</B> Process, UNIX<BR>

<B>Return Value:</B> SCALAR, the current priority associated with

the parameters.<BR>

<B>Definition:</B> Returns the current priority of <TT>WHO</TT>

(the pid, group pid, uid, or 0 for the current process). The <TT>WHICH</TT>

parameter can one of <TT>PRIO_PROCESS</TT>

(0), <TT>PRIO_PGGRP</TT> (1), <TT>PRIO_USER</TT>

(2).

<BLOCKQUOTE>

<PRE>

print(&quot;getpriority() &quot;, getpriority(0, 0), &quot;\n&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="getprotobynameNAME">

getprotobyname (NAME)</A></H3>

<P>

<B>Category:</B> Protocols, UNIX<BR>

<B>Return Value: </B>in Scalar Context: The protocol number assigned

to <TT>NAME</TT>.<BR>

<B>Return Value in Array Context:</B> (<TT>$name</TT>,

<TT>$aliases</TT>, <TT>$proto</TT>)