Dave’s Ramblings

To Begin: Create a File

Our first step is to create a file so we have something to read. Suppose we want to store a few pro wrestler's names and some other data about them, like their crowd reaction and favorite moves. For this, we could put each wrestler on a line, and separate the wrestler's information using a separator character (delimeter). One that is often used for separation is the pipe symbol ( | ). We will use it here to separate our data. Here is what we want to store:

Wrestler Name, Crowd Reaction, Favorite Move
The Rock,Cheer,Rock Bottom
Triple H,Boo,Pedigree
Stone Cold,Cheer,Stone Cold Stunner

Now, we can take this data and put it in a file in a similar way. We won't use the headings, just the wrestlers and their information:

The Rock|Cheer|Rock Bottom
Triple H|Boo|Pedigree
Stone Cold|Cheer|Stone Cold Stunner

Each wrestler has a new line for his information, and the information on each line is separated with the pipe symbol. Remember to be sure the new line is started after the last entry (hit "enter" right after the last character but don't put anything on the new line). This is so Perl sees a "\n" character at the end of each line. When we chop the lines after reading them in, this will keep the last character from being chopped instead. Just be sure there is no new data (even a space) on the new line though, or it will read it as a new line of information.

Once it is ready, we can save it as some type of text file. We can use lots of extensions, such as .txt, .dat, or other things. However, if someone stumbles onto the file in their browser, they can easily read the contents. One thing that helps a little is to give it the same extension as your executable cgi scripts. This way, the server tries to execute the file if it is called from a browser, and should return a permission error or an internal server error. If your server executes files with the .cgi extension (ask your host, some use .pl or others instead), then save the file with that extension, like:

wrestledata.cgi

Once it is saved, be sure the file has the permissions set so it is readable (755 should be OK here, if you plan to write to it you may want to use 777). Once that is done, we need to make a script which will use it. For ease of writing and of having the right location for the file, we will assume the data file and script will be in the same directory. If you choose to use separate directories, be sure to make those changes.

Opening the File

Within our script, we will want to read the data into our script. In order to do so, we must first open the file. We do this with a command like this:

The HANDLE above is something you will use to reference the file when you read from it and when you close it. The FileName/Location is the actual location of the file. Since we will have them in the same directory, we can just use the filename. If you have it in another directory, use the server path to the file. Here is how we can open our file:

Of course, you may want to assign the filename to a variable, so you could change it later more easily if you need to:

One last bit on the opening of the file. You may want to have an option to show an error if the file cannot be opened. So, we can add the "die" option to print the error to standard output. What we will do is use the open command, give the "or" option (two pipe symbols) and use the "die" routine as the option:

Reading the File

Now we are able to read from the open file. The easiest way to do this is to just assign the contents of the file to an array:

This will take everything from the file and toss it into the @raw_data array. Notice the use of the DAT handle for reading, with the < and > around it. We can then use the array to grab the information later, so that we can go ahead and close the file.

Close the File!

We have to be sure to remember to close the file when we are done with it, so we close it with the close command:

Again, the DAT handle is used to reference the file and close it. So now we have:

This is enough to read in the data, but if we want to make use of it we will want to pull it out of the array and do something with it.

Now we will get the data out of the array with a loop and the split method.

Making Use of the Data

To make use of the data, we need a purpose. So, let's say we want to print out a simple sentence for each wrestler in the list. We want to say the name, how the crowd might react, and the favorite move. Something like:

When (wrestler name) is in the ring, the crowd might (reaction) when the (move) is used.

To do this for each wrestler, we can use a loop to cycle through the content of the @raw_data array, grab the variables we want, and use them. This is commonly done with a foreach loop:

So, the $LINE_VAR is a variable to represent each line in the array. The @ARRAY will be the name of the array to loop through. For our example, we could use:

Now we need to do something inside the loop to split each line into variables we can use. Before we invoke the split though, we will want to chop the \n character off the end of each line:

Now we are ready to use the split method to create the variables we need each time through the loop. Since we used the pipe symbol as the separator, that is the character we will use to split the data. Notice that the pipe symbol needs to be escaped with a \ character since it is a special character in Perl:

Now we can print the sentence using the variables we created, and it will print the sentence for every wrestler.

That little bit will get us:

When The Rock is in the ring, the crowd might Cheer when the Rock Bottom is used.
When Triple H is in the ring, the crowd might Boo when the Pedigree is used.
When Stone Cold is in the ring, the crowd might Cheer when the Stone Cold Stunner is used.

And there you have it. Of course, you probably want HTML output instead of output for the console. Also, you might want to see the entire script in one piece. So, here is a full script which should give you the same type of output, except it will be an HTML page:

Substring (substr)

The substring function is a way to get a portion of a string value, rather than using the entire value. The value can then be used in a loop or a conditional statement, or just for its own purposes. For this one, you will probably want the general form of the function first. The function is usually set to a variable so that the variable contains the value of the substring:

$portion = substr($string_variable, start number, length);

Your $string_variable will be the variable from which you wish to create the substring. The start number is the character within the string from which you want to start your substring. Remember, though- the first number in a string here is zero rather than 1, so be careful when you make the count. The length above is the amount of characters you wish to take out of the string.

So, if we had a variable named $toy with a value of "baseball", but we wanted to get the last four characters rather than the full string, we would write something like this:

Yes, the substring turns out to be "ball". It starts at the fith character (which is 4 since the string starts with zero), and uses the next 4 characters. This function can be quite handy when you are trying to get part of a string later.

Length

The length function simply gives you back the number of characters in a string variable. This is handy when you don't know the value of the variable but would like to know the number of characters it has. It is useful with arrays, conditional statements, loops, and such things.

So, if you had a variable named $gold and its value was the string "precious", you could get the length of the string "precious" with the length function:

Since the string "precious" has 8 characters, $length_gold variable will be 8.

Chop & Chomp

The chop function is used to "chop off" the last character of a string variable. It will remove that last character no matter what it is, so it should be used with caution. For example:

me
myself
you

If you had read the "me" line in and assigned it to a variable, say $who_am _I, the value you have for it should be:

me\n

Remembering /n is the same as a carriage return.

The chop command would look like this (assuming we assigned "me\n" to a variable named $who_am_I):

Using the chop function in this case will remove the \n character. However, suppose we use it on the last of the three:

me
myself
you

The "you" is the last piece of text in the file, and could be missing the newline \n character if it was, for instance, typed into the file manually and the "Enter" key was not pressed afterward. If the chop command is used in such a case, it will remove the "u", which was not intended! So code such as:

This would result in the viewer seeing "You are yo!" rather than the expected result.

Now we look at the chomp function.

The chomp function will remove the last character of a string, but only if that character is an input record separator (the current value of $/ in Perl), which defaults to the newline (\n) character. This is often used to remove the \n character when reading from a file. The chomp function is much safer than the chop function for this, as it will not remove the last character if it is not \n.

Now if we run the chomp command on that last line instead, it won't remove the "u".

Now the viewer will see "You are you!" even if there was no \n character at the end of the "you" line.

Simple enough, each having their own purpose in a given circumstance. Chomp being more common as it's less likely to chop off bits you wanted.

Changing & Adding Elements
To change an array element, you can just access it with its list number and assign it a new value:

This changes the value of the element with the list number two (remember, arrays start counting at zero- so the element with the list number two is actually the third element). So, we changed "Opera" to "Mosaic", thus the array now contains "NS", "IE", and "Mosaic".

Now, suppose we want to add a new element to the array. We can add a new element in the last position by just assigning the next position a value. If it doesn't exist, it is added on to the end:

Now, we've added an element, "NS", "IE", "Opera", and "Mosaic".

Splice Function

Using the splice function, you can delete or replace elements within the array. For instance, if you simply want to delete an element, you could write:

You'll see three arguments inside the () of the splice function above. The first one is just the name of the array you want to splice. The second is the list number of the element where you wish to start the splice (starts counting at zero). The third is the number of elements you wish to splice. In this case, we just want to splice one element so we have 1. The code above deletes the element at list number 1, which is "IE" (NS is zero, IE is 1, Opera is 2). So now the array has only "NS" and "Opera", just two elements.

If you want to delete more than one element, change that third number to the number of elements you wish to delete. Let's say we want to get rid of both "NS" and "IE". We could write:

Now, it starts splicing at list number zero, and continues until it splices two elements in a row. Now all that will be left in the array is "Opera".

You can also use splice to replace elements. You just need to list your replacement elements after your other three arguments within the splice function. So, if we wanted to replace "IE" and "Opera" with "NeoPlanet" and "Mosaic", we would write it this way:

Now the array contains the elements "NS", "NeoPlanet", and "Mosaic". As you can see, the splice function can come in handy if you need to make large deletions or replacements.

Unshift/Shift
If you want to simply add or delete an element from the left side of an array (element zero), you can use the unshift and shift functions. To add an element to the left side, you would use the unshift function and write something like this:

As you can see, the first argument tells you which array to operate on, and the second lets you specify an element to be added to the array. So, "Mosaic" takes over position zero and the array now has the four elements "Mosaic", "NS", "IE", and "Opera".

To delete an element from the left side, you would use the shift function. All you have to do here is give the array name as an argument, and the element on the left side is deleted:

Now, the array has only two elements: "IE" and "Opera".

You can keep the value you deleted from the array by assigning the shift function to a variable:

Now the array has only "IE" and "Opera", but you have the variable $old_first_element with the value of "NS" so you can make use of it after taking it from the array.

Push/Pop

These two functions are just like unshift and shift, except they add or delete from the right side of an array (the last position). So, if you want to add an element to the end of an array, you would use the push function:

Now, you have an array with "NS", "IE", "Opera", and Mosaic".

To delete from the right side, you would use the pop function:

Now the array has only "NS" and "IE", but you have the variable $last_element with the value of "Opera" so you can make use of it after taking it from the array.

Chop

If you want to take the last character of each element in an array and "chop it off", or delete it, you can use the chop function. This comes in handy later when we are reading from a file, where we would need to chop the new line (\n) character from each line in a file. For now, let's just see how to use it. You would just write something like this:

This code would take the numbers off the end of each element, so we would be left with "NS", "IE" and "Opera".

Sort

If you want to sort the elements of an array, this can come in handy. You can sort in ascending or descending order with numbers or strings. Numbers will go by the size of the number, strings will go in alphabetical order.

The sub from above is a subroutine, much like what is called a "function" in other languages. We will explain that in more detail later. As you can see, the code above would sort in ascending order, so it would sort our array in alphabetical order. So, we have: "IE", "NS", and "Opera" as the new order. If you want it in reverse alphabetical order, you would use $b < => $a in place of the $a < => $b above. You could change the name of the subroutine to whatever you wish, just be sure you call the subroutine with the same name. This will make a bit more sense after we get to the section on subroutines and reading from files.

Reverse

You can reverse the order of the array elements with the reverse function. You would just write:

Now, the order changes to "Opera", "IE", and "NS".

Join

You can create a flat file database from your array with the join function. Again, this is more useful if you are reading and writing form files. For now, what you will want to know is that it allows you to use a delimiter (a character of your choice) to separate array elements. The function creates a variable for each element, joined by your delimiter. So, if you want to place a : between each element, you would write:

This would create something like this:

NS:IE:Opera

Split
The split function is very handy when dealing with strings. It allows you to create an array of elements by splitting a string every time a certain delimiter (a character of your choice) shows up within the string. Suppose we had the string:

NS:IE:Opera

Using the split function, we could create an array with the elements "NS", "IE", and "Opera" by splitting the string on the colon delimiter (:). We could write:

Notice in the split function that you place your delimiter between two forward slashes. You then place the string you want to split as the second argument, in this case the string was the value of the $browser_list variable. Setting it equal to @browser creates the @browser array from the split.