A first Perl script, by The Linux Information Project (LINFO)Perl (short for Practical Extraction and Report Language) is one of the most popular programming languages. It was developed by Larry Wall, who was trained as a linguist, mainly for processing text, but it is now also used for a much broader range of applications, particularly systems administration and web development. Moreover, it is free software; that is, it is free both in a monetary sense and with regard to use. An easy way to see if it has actually been installed on any machine is to type in the following command and then press the ENTER key. Perl command. The - voption causes it to tell the version that is installed. A script is a simple program. This line informs the system that the file is a Perl script and tells it the location of the Perl executable and associated files. It is referred to as the shebang line because the pound sign followed by an exclamation mark is called a shebang. Shebangs are used in other scripting languages as well. It tells Perl to display what follows it in quotes on the display monitor or to write it to a file. The \n represents the newline character; it tells Perl to begin a new, blank line on the screen following the text. Note that this line ends in a semicolon, as is the case for statements (i. However, this can easily be changed by using the chmod command (which is used to change permissions). Assuming that the file is named perl. The program is now ready to run. It can be run by merely issuing the perl command and using the name of the new file as an argument (i. If all goes well, the text Hello to the world! If it has, a very likely cause of the problem is that the . Another possibility is that there is some error in the spelling of the file name when using that command. Thus, the next step should be to open the file with a text editor to confirm that it actually contains the text that was intended to be written to it. The text could be missing, particular if the cat command was used incorrectly. Also, it should be confirmed that the text is written exactly as shown in the example above, particularly that the semicolon is included at the end of the line. Forgetting to put the semicolon at the end of a statement is one of the most common programming errors. Before going on to more advanced programs, however, it can be instructive to conduct several simple experiments with this program. An example is to replace it with something like This is my first Perl script. The changes could also include omitting the newline character or using two newline characters, with the resulting program looking like print . These changes can be made to the original file, or a new file (with a new name) can be created. An extremely simple program such as this may work, but it is not good programming practice and more complex programs will generate an error message. For example, it can be seen that removing one or both sets of double quotation marks will result in an error message such as Can't find string terminator '. It can be observed that replacing the two sets of double quotes with two single quotes will change how perl interprets the program: it will cause the \n to just be interpreted as text rather than as an instruction to begin a new line.
For each thing you want to test your program. Simple is explicitly tested all the way back to perl 5.6.0. He observed that the main problem is not dealing with these edge cases but that people hate to write. So you find the Perl docs on modules a bit confusing? I don't turn on warnings in modules that I write but I do make a point of testing them with warnings. Simple Module Tutorial by johnnywang on Aug.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
December 2016
Categories |