It often happens that you need to work with only a few elements from a given list. For example, the Bedrock Library keeps information about their patrons in a large file. Each line in the file describes one patron … Read the rest
The simplest way to launch a child process in Perl to run a program is the system function. For example, to invoke the Unix date command from within Perl, it looks like:
system "date";
The child process … Read the rest
The smart match operator, ~~, looks at both of its operands and decides on its own how it should compare them. If the operands look like numbers, it does a numeric comparison. If they look … Read the rest
Finding a substring depends on where you have lost it. If you happen to have lost it within a bigger string, you’re in luck because the index function can help you out. Here’s how it … Read the rest
Your program runs with a “working directory,” which is the starting point for relative pathnames. That is, if you refer to the file fred, that means fred in the current working directory.
The chdir … Read the rest
Before we start a program that creates a new file, let’s make sure that the file doesn’t already exist so that we don’t accidentally overwrite a vital spreadsheet datafile or that important birthday calendar. For this, we … Read the rest
There is a lot more to Perl than what we’re able to show you in this book, and there are a lot of people doing a lot of interesting things with Perl. If there is a problem to solve, then … Read the rest
In an if control structure, the block of code is executed only when the conditional expression is true. If you want to execute a block of code only when the conditional is false, change … Read the rest
If you think of the m// pattern match as being like your word processor’s “search” feature, the “search and replace” feature would be Perl’s s/// substitution operator. This simply replaces whatever part of a variable matches a … Read the rest
We’ve been writing patterns in pairs of forward slashes, like /fred/. But this is actually a shortcut for the m// (pattern match) operator. As you saw with the qw// operator, you may choose any pair of … Read the rest