1. Computing

Parsing Text Files

How to parse simple text files with Perl

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Let's take a minute to look at one of the reasons Perl makes a great data mining and scripting tool - parsing text files. Big or small, Perl benchmarks great when it comes to digging through text. As an example, lets build a little program that opens up a tab separated data file, and parses the columns into something we can use.

Say for example your boss hands you a file with a list of names, emails and phone numbers and wants you to read the file and do something with the information like put it into a database or just print it out in a nicely formatted report. The file's columns are separated with the TAB character and would look something like this:

 Larry larry@example.com 111-1111
 Curly curly@example.com 222-2222
 Moe moe@example.com 333-3333 
Here's the full listing we'll be working with:
 #!/usr/bin/perl
 
 open (FILE, 'data.txt');
 while (<FILE>) {
 chomp;
 ($name, $email, $phone) = split("\t");
 print "Name: $name\n";
 print "Email: $email\n";
 print "Phone: $phone\n";
 print "---------\n";
 }
 close (FILE);
 exit;
 
Note that this pulls some code from the how to read and write files in Perl tutorial that I've already set up. Take a look at that if you need a refresher. First it opens a file called data.txt (that should reside in the same directory as the Perl script). Then it reads the file into the catchall variable $_ line by line. In this case, the $_ is implied and not actually used in the code.

After reading in a line, any whitespace is chomped off the end of it. Then the split function is used to break the line on the tab character. In this case the tab is represented by the code \t. To the left of the split's sign, you'll see that I'm assigning a group of three different variables. These represent one for each column of the line.

Finally, each variable that has been split from the file's line is printed separately so that you can see how to access each column's data individually. The output of the script should look something like this:

 Name: Larry
 Email: larry@example.com
 Phone: 111-1111
 ---------
 Name: Curly
 Email: curly@example.com
 Phone: 222-2222
 ---------
 Name: Moe
 Email: moe@example.com
 Phone: 333-3333
 --------- 
Although in this example we're just printing out the data, it would be trivially easy to store that same information parsed from a TSV or CSV file in a full fledged database.
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