ch25.htm

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

</BLOCKQUOTE>



</TD></TR>

</TABLE>

</CENTER>

<P>

<H3><A NAME="chownNUMERICALUIDNUMERICALGIDLIST">

chown (NUMERICAL_UID, NUMERICAL_GID, LIST)</A></H3>

<P>

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

<B>Return Value:</B> SCALAR, the number of files successfully

changed.<BR>

<B>Definition:</B> Changes the ownership of the files in <TT>LIST</TT>

to the user ID and the group ID specified as parameters.

<BLOCKQUOTE>

<PRE>

chown(1, 1, &quot;test1.txt&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="chrNUMBER">

chr (NUMBER)</A></H3>

<P>

<B>Category:</B> String<BR>

<B>Return Value:</B> SCALAR, the character represented by <TT>NUMBER</TT>.

<BR>

<B>Definition:</B> Returns the ASCII character represented by

<TT>NUMBER</TT>. For example, <TT>chr(69)</TT>

is the letter E. See Appendix E, &quot;ASCII Table&quot; for more

information.

<H3><A NAME="chrootDIRNAME">

chroot (DIR_NAME)</A></H3>

<P>

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

<B>Return Value:</B> SCALAR, true if successful, false otherwise.

<BR>

<B>Definition:</B> Changes the root directory of the current process

to <TT>DIR_NAME</TT>. Which means

that a filename like <TT>/john.dat</TT>

might really refer to <TT>/root/users/~jmiller/john.dat</TT>.

<BLOCKQUOTE>

<PRE>

chroot(&quot;/usr/~waters&quot;);<BR>



</PRE>

</BLOCKQUOTE>

<p>

<CENTER>

<TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>

<TR><TD><B>Tip</B></TD></TR>

<TR><TD>

<BLOCKQUOTE>

Your process must have superuser rights in order to successfully use this fuNCtion. It is used to make processes safer by only allowing them access to the subdirectory tree relevant to their purpose.</BLOCKQUOTE>



</TD></TR>

</TABLE>

</CENTER>

<P>

<H3><A NAME="closeFILEHANDLE">

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

<P>

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

<B>Return Value:</B> SCALAR, true if the file was closed correctly,

false if not.<BR>

<B>Definition:</B> Closes the file opened with <TT>FILEHANDLE</TT>.

This operation flushes all buffered output. If the file handle

refers to a pipe the Perl program waits until the process being

piped to has finished.

<BLOCKQUOTE>

<PRE>

open(FILE, &quot;test1.txt&quot;);

# some file activity

close(FILE);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="closedirDIRHANDLE">

closedir (DIRHANDLE)</A></H3>

<P>

<B>Category:</B> Directory, Files<BR>

<B>Return Value:</B> SCALAR, true if the directory was closed

correctly, false if not.<BR>

<B>Definition:</B> Closes the directory opened by <TT>opendir()</TT>.

<BLOCKQUOTE>

<PRE>

opendir(DIR, &quot;.&quot;);

# some directory activity

closedir(DIR);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="connectSOCKETNAME">

connect (SOCKET, NAME)</A></H3>

<P>

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

<B>Return Value:</B> SCALAR, true if the connection was successful,

otherwise false.<BR>

<B>Definition:</B> Attempts to connect to a remote socket. <TT>NAME</TT>

must be a packed address of the correct type for the socket.

<H3><A NAME="cosEXPR">

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

<P>

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

<B>Return Value:</B> SCALAR, the cosine of <TT>EXPR</TT>

or else <TT>$_</TT> is used if no

expression is specified.<BR>

<B>Definition:</B> Calculates a cosine.

<BLOCKQUOTE>

<PRE>

$temp = cos(60);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="cryptTEXTSALT">

crypt (TEXT, SALT)</A></H3>

<P>

<B>Category:</B> String<BR>

<B>Return Value:</B> SCALAR, an eNCrypted string.<BR>

<B>Definition:</B> ENCrypts <TT>TEXT</TT>

using a key (either <TT>SALT</TT>

or the first two letters of <TT>TEXT</TT>).

<BLOCKQUOTE>

<PRE>

$eNCyptedString = crypt(&quot;Password&quot;,&quot;TR&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="dbmcloseHASH">

dbmclose (HASH)</A></H3>

<P>

<B>Category:</B> Database<BR>

<B>Return Value:</B> SCALAR, true if the close was successful,

false otherwise.<BR>

<B>Definition:</B> Undoes the linking of <TT>HASH</TT>

to a dbm file.<BR>

<p>

<CENTER>

<TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>

<TR><TD><B>Tip</B></TD></TR>

<TR><TD>

<BLOCKQUOTE>

This fuNCtion has been superseded by the <TT>untie()</TT> fuNCtion.

</BLOCKQUOTE>



</TD></TR>

</TABLE>

</CENTER>

<P>

<H3><A NAME="dbmopenHASHDATABASENAMEMODE">

dbmopen (HASH, DATABASE_NAME, MODE)</A></H3>

<P>

<B>Category:</B> Database<BR>

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

<B>Definition:</B> Links <TT>HASH</TT>

to <TT>DATABASE_NAME</TT>. If the

database does not exist, a new one with the specified <TT>MODE</TT>

will be created.<BR>

<p>

<CENTER>

<TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>

<TR><TD><B>Tip</B></TD></TR>

<TR><TD>

<BLOCKQUOTE>

This fuNCtion has been superseded by the <TT>tie()</TT> fuNCtion.

</BLOCKQUOTE>



</TD></TR>

</TABLE>

</CENTER>

<P>

<H3><A NAME="definedEXPR">

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

<P>

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

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

has a real value, false otherwise.<BR>

<B>Definition:</B> There is a subtle distiNCtion between an undefined

null value and a defined null value. Some fuNCtions return undefined

null to indicate errors, while others return a defined null to

indicate a particular result (use a comparison with the null string

to test for this rather than using <TT>defined()</TT>).

<BLOCKQUOTE>

<PRE>

@iexist = (1,2,3);

print(&quot;exists.\n&quot;) if defined(@iexist);

print(&quot;does not exist.\n&quot;) unless defined(@iexist);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="deleteEXPR">

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

<P>

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

<B>Return Value:</B> SCALAR, the deleted value or the undefined

value if nothing was deleted.<BR>

<B>Definition:</B> Deletes an entry from an associative array.

<TT>EXPR</TT> is the key for the entry

to delete.

<BLOCKQUOTE>

<PRE>

%Hash = ('Jan' =&gt; 'One', 'Feb' =&gt; 'Two', 'Mar' =&gt; 'Three');

delete($Hash{'Jan'});

</PRE>

</BLOCKQUOTE>

<H3><A NAME="dieLIST">

die ([LIST])</A></H3>

<P>

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

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

<B>Definition:</B> Terminates execution of the Perl script, printing

<TT>LIST</TT> to STDERR. The exit

value is the current value of <TT>$!</TT>

which may have been set by a previous fuNCtion. If <TT>$!</TT>

has a value of zero, <TT>$?</TT> will

be returned instead. If <TT>$?</TT>

is zero, it exits with an exit value of 255. If <TT>LIST</TT>

does not end in a newline, the text similar to &quot;at test.pl

at line 10&quot; will be appended to the end.

<BLOCKQUOTE>

<PRE>

die(&quot;Something fatal has happened and the script must die!&quot;);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="doSCRIPTNAME">

do (SCRIPTNAME)</A></H3>

<P>

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

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

<B>Definition:</B> Executes the contents of a file as a Perl script.

It is usually used to iNClude subroutines however it has been

mostly superseded by <TT>use()</TT>

and <TT>require()</TT>.

<H3><A NAME="dumpLABEL">

dump ([LABEL])</A></H3>

<P>

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

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

<B>Definition:</B> Causes the program to create a binary image

or core dump. You can reload the image using undump program. When

reloaded, the program begins execution from the optional label

specified. So it is possible to set up a program which initializes

data structures to <TT>dump()</TT>

after the initialization so that execution is faster when reloading

the dumped image.

<H3><A NAME="eachHASH">

each (HASH)</A></H3>

<P>

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

<B>Return Value:</B> ARRAY, an entry (the key-value pair) in <TT>HASH</TT>.

<BR>

<B>Definition:</B> Allows iteration over the entries in an associative

array. Each time it is evaluated, another key-value pair is returned.

When all the entries have been returned, it returns an empty array.

<BLOCKQUOTE>

<PRE>

%NumberWord = ('1' =&gt; 'One', '2' =&gt; 'Two', '3' =&gt; 'Three');

while (($key, $value) = each(%NumberWord)) {

    print(&quot;$key: $value\n&quot;);

}

</PRE>

</BLOCKQUOTE>

<H3><A NAME="endgrent">

endgrent ( )</A></H3>

<P>

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

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

<BR>

<B>Definition:</B> Closes the <TT>/etc/group</TT>

file used by <TT>getgrent()</TT> and

other group related fuNCtions.

<BLOCKQUOTE>

<PRE>

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

endgrent();

</PRE>

</BLOCKQUOTE>

<H3><A NAME="endhostent">

endhostent ( )</A></H3>

<P>

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

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

<BR>

<B>Definition:</B> Closes the TCP socket used by <TT>gethostbyname()</TT>

and host related fuNCtions.

<BLOCKQUOTE>

<PRE>

$host = gethostbyname(&quot;lyNCh&quot;);

endhostent();

</PRE>

</BLOCKQUOTE>

<H3><A NAME="endnetent">

endnetent ( )</A></H3>

<P>

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

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

<BR>

<B>Definition:</B> Closes the <TT>/etc/networks</TT>

file used by <TT>getnetent()</TT>

and network related fuNCtions.

<BLOCKQUOTE>

<PRE>

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

endnetent();

</PRE>

</BLOCKQUOTE>

<H3><A NAME="endprotoent">

endprotoent ( )</A></H3>

<P>

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

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

<BR>

<B>Definition:</B> Closes the <TT>/etc/protocols</TT>

file used by <TT>getprotoent()</TT>

and protocol related fuNCtions.

<BLOCKQUOTE>

<PRE>

($name, $alias, $protocol) = getprotoent();

endprotoent();

</PRE>

</BLOCKQUOTE>

<H3><A NAME="endpwent">

endpwent ( )</A></H3>

<P>

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

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

<BR>

<B>Definition:</B> Closes the <TT>/etc/passwd

file</TT> used by <TT>getpwent()</TT>

and password related fuNCtions.

<BLOCKQUOTE>

<PRE>

($name, $pass, $uid, $gid, $quota, $name, 

    $gcos, $logindir, $shell) = getpwent();

endpwent();

</PRE>

</BLOCKQUOTE>

<H3><A NAME="endservent">

endservent ( )</A></H3>

<P>

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

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

<BR>

<B>Definition:</B> Closes the <TT>/etc/servers</TT>

file used by <TT>getservent()</TT>

and related fuNCtions.

<BLOCKQUOTE>

<PRE>

($name, $aliases, $port, $protocol) = getservent();

endservent();

</PRE>

</BLOCKQUOTE>

<H3><A NAME="eofFILEHANDLE">

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

<P>

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

<B>Return Value:</B> SCALAR, true if the next read on <TT>FILEHANDLE</TT>

will be at the end of file, false if not.<BR>

<B>Definition:</B> Tests for the end of a file. This is done by

reading the next character and then undoing this operation (so

is only suitable on files where this can be done safely). If no

argument is supplied the file tested is the last file which was

read. If the empty list is supplied then a pseudo file is created

of the files listed on the command line. This lets you test for

the end of the last file on the command line.

<BLOCKQUOTE>

<PRE>

open(FILE, &quot;test1.txt&quot;);

# some file activity

print(&quot;eof() returned &quot;, eof(FILE) ? &quot;TRUE&quot; : &quot;FALSE&quot;, &quot;\n&quot;);

close(FILE);

</PRE>

</BLOCKQUOTE>

<H3><A NAME="evalEXPRBLOCK">

eval ([EXPR | BLOCK])</A></H3>

<P>

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

<B>Return Value:</B> The undefined value if a syntax error, a

runtime error, or a <TT>die()</TT>

fuNCtion occurs. Otherwise, the return value is the value of <TT>EXPR</TT>

or the last statement in <TT>BLOCK</TT>.

The return value can be any type.<BR>

<B>Definition:</B> Treats the expression like a Perl program and

executes it. As the context of this execution is the same as that

of the script itself, variable definitions and subroutine definitions

persist. Syntax errors, runtime errors, and execution of the <TT>die()</TT>

fuNCtion are trapped and an undefined result is returned. If such

an error does occur <TT>$@</TT> is

set. <TT>$@</TT> will be equal to

a defined null string if no errors are found. If no expression

is supplied, <TT>$_</TT> is the default

argument. If the block syntax is used then the expressions in

the block are evaluated only oNCe within the script (which may

be more efficient for certain situations).<BR>

<p>

<CENTER>

<TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>

<TR><TD><B>Tip</B></TD></TR>

<TR><TD>

<BLOCKQUOTE>

<TT>eval()</TT> traps possible error conditions which would otherwise crash a program and so can be used to test if certain features are available which would cause runtime errors if used when not available. See <A HREF="ch13.htm" >Chapter 13</A>, 
&quot;Handling Errors and Signals,&quot; for more information.

</BLOCKQUOTE>



</TD></TR>

</TABLE>