Parsing HTML with Perl. handle DATA while my anchor. In one case I had to process large sets of HTML files I had to process where each. Returns the number of characters actually read, 0 at end of file. An OFFSET may be specified to place the read data at some place in the. perldoc. perl. org. How to parse binary data with Perl. Read a few bytes. All binary files have a specific format that they follow. In the case of the zoneinfo files. Managing Rich Data Structures. One of my scripts created HTML for a clickable. A Perl script can read data from a DBM file as if it were contained in a hash. SIMPLE file reading in Perl. Ren and Konerak wrote a couple of pretty good responses that show how to open and read a file. Unfortunately they have some issues in terms of promoting best practices. So, Ill come late to the party and try to add clear explanation of best practices approach and why it is better to use the best practice approach. What is a file handle A file handle is a name we use that represents the file itself. When you want to operate on a file read it, write to it, move around, etc. use the file handle to indicate which file to operate on. A file handle is distinct from the files name or path. Variable scope and file handles. A variables scope determines in what parts of a program the variable can be seen. In general, it is a good idea to keep the scope on every variable as small possible so that different parts of a complex program dont break each other. The easiest way to strictly control a variables scope in Perl is to make it a lexical variable. Lexical variables are only visible inside the block in which they are declared. Use my to declare a lexical variable my foo Cant see foo here. Cant see foo here. Perl file handles can be global or lexical. When you use open with a bare word a literal string without quotes or a sigil, you create a global handle. When you open on an undefined lexical scalar, you create a lexical handle. FOO, file Global file handle. Lexical file handle. Another way to get a lexical handle. The big problem with global file handles is that they are visible anywhere in the program. So if I create a file handle named FOO in subroutine, I have to very careful to ensure that I dont use the same name in another routine, or if I use the same name, I must be absolutely certain that under no circumstances can they conflict with each other. The simple alternative is to use a lexical handle that cannot have the same kind of name conflicts. Analyzing HTML with Perl. I can simply run the program in the directory containing the HTML files. Had I read Wassermans article Automating Windows. How to read an Excel file in Perl How to create an Excel file with Perl Sending HTML email. to read the excel file examplesreadexcel. pl usrbinperl use. A short tutorial on how to open a file with Perl, and read the file contents. Perl files example How to open and read data files with Perl. Extract data from a spreadsheet usrbinperl use strict use warnings. Reading and writing to file Read a spreadsheet. C Read Data From FileAnother benefit of lexical handles is that it is easy to pass them around as subroutine arguments. The open function. The open function has all kinds of features. It can run subprocesses, read files, and even provide a handle for the contents of a scalar. You can feed it many different types of argument lists. It is very powerful and flexible, but these features come with some gotchas executing subprocesses is not something you want to do by accident. For the simple case of opening a file, it is best to always use the 3 argument form because it prevents unintended activation of all those special features open FILEHANDLE, MODE, FILEPATH. FILEHANDLE is the file handle to open. MODE is how to open the file, for overwrite, for write in append mode, for read and write, andlt for read. FILEPATH is the path to the file to open. On success, open returns a true value. On failure, is set to indicate the error, and a false value is returned. So, to make a lexical file handle with a 3 argument open that we can use to read a file open my fh, lt, filepath. The logical return values make it easy to check for errors open my fh, lt, filepath. Error opening filepath n. I like to bring the error handling down to a new line and indent it, but thats personal style. Closing handles. When you use global handles it is critical to carefully, explicitly close each and every handle when you are done with it. Failure to do so can lead to odd bugs and maintainability problems. FOO. Lexical handles automatically close when the variable is destroyed when the reference count drops to 0, usually when the variable goes out of scope. When using lexical handles it is common to rely on the implicit closure of handles rather than explicitly closing them. Diamonds are a Perls best friend. The diamond operator, lt, allows us to iterate over a file handle. Like open it has superpowers. Well ignore most of them for now. Search for info on the input record separator, output record separator and the NULL file handle to learn about them, though. The important thing is that in scalar context e. In list context e. Imagine you want to read a data file with three header lines date, time and location and a bunch of data lines open my fh, lt, filepath. Ugh n. my date lt fh. Its common in to hear people talk about slurping a file. This means to read the whole file into a variable at once. Slurp into array. Slurp into a scalar uses tricks outside the scope of this answer. Putting it all togetheropen my fh, lt, myfile. Error opening file n. Putting it all together special extra credit editionmy fh gethandle myfile. Get the lines before banana. Skip some lines. my potato readuntil fh, qrpotato Get the lines before potato. Cant open filepath for reading n. Why so many different ways Why so many gotchas Perl is an old language it has baggage dating all the way back to 1. Over the years various design issues were found and fixes were made but only rarely were fixes allowed to harm backwards compatibility. Further, Perl is designed to give you the flexibility to do what you want to, when you want to. It is very permissive. The good thing about this is that you can reach down into the murky depths and do really cool magical stuff. The bad thing is that it is easy to shoot yourself in the foot if you forget to temper your exuberance and fail to focus on producing readable code. Just because youve got more than enough rope, doesnt mean that you have to hang yourself.