Many times in Perl applications you need to be able to create a temporary file (a Perl temp file). In this scenario you don't want to get into the system-specific details of temporary directories and things like that; you just want to create and use a temporary file.
Here are some Perl code snippets that should help get you started down this road.
How to use the Perl stat function.
Problem: Using Perl, you need to determine the last time a file was accessed (read) or updated (modified).
Solution: Use the Perl stat function to get this information. Let's look at a couple of short examples to see how this works.
To determine the last access (read) time of a file named foo.txt, use this sample Perl code:
Perl FAQ: How do I determine the size of a file from within a Perl program/script?
Just use the Perl stat function to get the file size. Here is a quick example.
To determine size of a file named foo.txt, just use a little Perl code like this:
Perl has a couple of convenient file operators that let you determine when a file was last accessed or modified in units of days. These operators are:
-M The modification age of the file, in days -A The access age of the file, in days
You can use these Perl file test operators in your scripts to determine when files are getting "old" (where the definition of "old" is up to you).
Perl file writing FAQ: How can I test to see if I can write to a file in Perl?
In Perl it's very simple to determine whether you can write to a file. Just use the Perl -w file operator, as shown in this example:
A common Perl FAQ is "How do I do (something) for every file in a directory?"
Here's some sample code that will show you how to loop through each file in a directory:
Perl file copying FAQ: How do I copy a file in Perl?
You can copy a file in Perl using the File::Copy module. Here's a quick example:
Perl FAQ: "How can I process every file in a directory that matches a certain filename pattern?"
There are several ways to do this, but I normally use the glob function, because I can remember the syntax pretty easily.
Let's look at a couple of glob examples.
You can use the glob operator to get a list of all files in the current directory like this:
A Perl FAQ is "How do you concatenate (merge) two or more strings in Perl?"
The short answer is that you use the . operator. Here's a simple example:
$name = "alvin" . " " . "alexander";
Of course I could have also done that like this:
$name = "alvin " . "alexander";
but I wanted to show an example with more than two strings.
Summary: How to sort a Perl string array (when you don't have to worry about whether the strings are all uppercase or lowercase).
Perl excels at a number of tasks, especially text-processing, and if you have an array of strings, and all of the elements in the array are either uppercase or lowercase, sorting your string array is very easy. In this tutorial I'll show how to sort an array of strings, and will also show how to sort your string array in reverse order.
Perl substring FAQ: Can you demonstrate some Perl substring examples?
As a language, Perl is very good at text processing, including dealing with strings and substrings. In this article we'll take a look at some Perl substring manipulations we can perform.
For the purposes of our Perl substring tutorial, let's assume that we have a string defined like this:
With Perl we work with strings and arrays (or lists) of strings all the time. I thought I'd take a few moments here to show the most common ways to create a Perl string array, and also to loop through (or iterate through) the list of strings I create.
When you first start to work with Perl, you might create a string array like the following example:
Perl substring FAQ: How do I extract a substring from a string?
Solution: Use the Perl substr function. The general substr syntax looks like this:
$my_substring = substr($full_string, $start_pos, $length);
A more specific Perl substring example is shown in the following code, where I extract the $firstname and $lastname strings from the $name string:
In a previous tutorial I demonstrated how you can search a Perl list/array of strings for another string, or a regular expression using Perl's grep function. In this example I'll demonstrate how you can search a list of numbers very easily, also using Perl's grep function.
Here's a quick example program that demonstrates how to access environment variables from within your Perl programs:
# environment variables are held in the %ENV hash
foreach $key (sort keys %ENV)
{
print "$key is $ENV{$key}\n";
}
Using this simple Perl foreach loop, here's a subset of the output this script prints on my MacBook Pro:
Free Perl editors FAQ: Can you recommend any good free Perl editors?
I had to get back into some Perl development for a recent project, and when I realized the project was going to take a few days to complete, I decided to look around to see if I could find a good free Perl editor.
Perl reverse array FAQ: Can you show an example of how to reverse a Perl array (reverse the Perl array contents)?
Sure. I just create a Perl script to print the contents of a text file in reverse order. I named this program rcat (for "reverse cat"), and I use it as a helper program with my transport command (a replacement for the Linux cd command). We can use it to demonstrate the Perl "reverse array" technique.
Perl array examples FAQ: Can you share some Perl array examples (Perl array programming examples)?
After doing a lot of work with Perl arrays recently, I thought I'd post a little collection of Perl array examples out here today. The Perl array syntax isn't too hard, but there are a few common mistakes you can make, so hopefully a simple reference page will help.
Perl hash "add" FAQ: How do I add a new element to a Perl hash? (Or, How do I push a new element onto a Perl hash?)
The Perl hash is a cool programming construct, and was very unique when I was learning programming languages in the late 1980s. A Perl hash is basically an array, but the keys of the array are strings instead of numbers.
To add a new element to a Perl hash, you use the following general syntax:
Recently I wrote a Perl subroutine tutorial, and a few people (correctly) gave me grief over using the ampersand operator ("&") when calling my Perl subroutines. I'm not going to spend a lot of time on this, but I think it's important for people to know when they have to use the ampersand operator when calling their subroutines.
