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Pod is a simple-to-use markup language used for writing documentation for Perl, Perl programs, and Perl modules. There are various translators available for converting Pod to various formats like plain text, HTML, man pages, and more. Pod markup consists of three basic kinds of paragraphs −Ordinary Paragraph − You can use formatting codes in ordinary paragraphs, for bold, italic, code-style , hyperlinks, and more.Verbatim Paragraph − Verbatim paragraphs are usually used for presenting a codeblock or other text which does not require any special parsing or formatting, and which shouldn't be wrapped.Command Paragraph − A command paragraph is used for ... Read More
Perl kill('KILL', (Process List)) function can be used to terminate a pseudo-process by passing it the ID returned by fork().Note that using kill('KILL', (Process List)) on a pseudo-process() may typically cause memory leaks, because the thread that implements the pseudo-process does not get a chance to clean up its resources.You can use kill() function to send any other signal to target processes, for example following will send SIGINT to a process IDs 104 and 102 −#!/usr/bin/perl kill('INT', 104, 102); 1;
Perl provides a fork() function that corresponds to the Unix system call of the same name. On most Unix-like platforms where the fork() system call is available, Perl's fork() simply calls it. On some platforms such as Windows where the fork() system call is not available, Perl can be built to emulate fork() at the interpreter level.The fork() function is used to clone a current process. This call create a new process running the same program at the same point. It returns the child pid to the parent process, 0 to the child process, or under if the fork is ... Read More
You can use system() Perl function to execute any Unix command, whose output will go to the output of the perl script. By default, it is the screen, i.e., STDOUT, but you can redirect it to any file by using redirection operator > −#!/usr/bin/perl system( "ls -l") 1;When above code is executed, it lists down all the files and directories available in the current directory −drwxr-xr-x 3 root root 4096 Sep 14 06:46 9-14 drwxr-xr-x 4 root root 4096 Sep 13 07:54 android -rw-r--r-- 1 root root 574 Sep 17 15:16 index.htm drwxr-xr-x 3 544 401 4096 Jul 6 16:49 MIME-Lite-3.01 ... Read More
This simplest way of executing any Unix command in Perl Program is by using backstick operator. You simply put your command inside the backstick operator, which will result in execution of the command and returns its result which can be stored as follows −#!/usr/bin/perl @files = `ls -l`; foreach $file (@files) { print $file; } 1;When the above code is executed, it lists down all the files and directories available in the current directory −drwxr-xr-x 3 root root 4096 Sep 14 06:46 9-14 drwxr-xr-x 4 root root 4096 Sep 13 07:54 android -rw-r--r-- 1 root root 574 Sep 17 ... Read More
A Perl module is a reusable package defined in a library file whose name is the same as the name of the package with a .pm as extension.A Perl module file called Foo.pm might contain statements like this.#!/usr/bin/perl package Foo; sub bar { print "Hello $_[0]" } sub blat { print "World $_[0]" } 1;Few important points about Perl modulesThe functions require and use will load a module.Both use the list of search paths in @INC to find the module.Both functions require and use call the eval function to process the code.The 1; at the bottom causes eval to evaluate to TRUE (and thus not ... Read More
You may define any number of code blocks named BEGIN and END in Perl programs, which act as constructors and destructors respectively.BEGIN { ... } END { ... } BEGIN { ... } END { ... }Every BEGIN block is executed after the perl script is loaded and compiled but before any other statement is executed.Every END block is executed just before the perl interpreter exits.The BEGIN and END blocks are particularly useful when creating Perl modules.Following example shows its usage −Example Live Demo#!/usr/bin/perl package Foo; print "Begin and Block Demo"; BEGIN { print "This is BEGIN Block" } END { ... Read More
The package statement in Perl switches the current naming context to a specified namespace (symbol table). Thus −A package is a collection of code which lives in its own namespace.A namespace is a named collection of unique variable names (also called a symbol table).Namespaces prevent variable name collisions between packages.Packages enable the construction of modules which, when used, won't clobber variables and functions outside of the modules's own namespace.The package stays in effect until either another package statement is invoked, or until the end of the current block or file.You can explicitly refer to variables within a package using the :: package ... Read More
Inter – frame SpacesInter − frame spaces (IFS) are waiting periods between transmission of frames operating in the medium access control (MAC) sublayer where carrier-sense multiple access with collision avoidance (CSMA/CA) is used. These are techniques used to prevent collisions as defined in IEEE 802.11-based WLAN standard (Wi-Fi).IFS is the time period between completion of the transmission of the last frame and starting transmission of the next frame apart from the variable back-off period.The diagram below shows the different types of inter − frame spacing starting from the shortest duration (highest priority) to the longest duration (lowest priority). Among these, ... Read More
Transmit opportunity (TXOP) is a MAC layer feature used in IEEE 802.11-based wireless local area network (WLAN). TXOP defines the time duration for which a station can send frames after it has gained contention for the transmission medium. By providing this contention-free time period, TXOP aims to increase the throughput of high priority data, such as voice and video.TXOP is available in Quality of Service as part of Enhanced Distributed Channel Access (EDCA).Working PrincipleTXOP operates in the following sequence of steps −When a station in the WLAN has frames to send, it waits till it’s Network Allocation Vector (NAV) decrements ... Read More