Regular Expressions :
PCRE and POSIX RegEx Solutions

Choose Your Weapon:

A Note on PCRE Implementations in Different Text-Editors
(and other tools with Regular Expression search, search/ replace capabilities)
It’s important to recognize that, even though they are based on regular expression syntax (hence the term Perl Compatible Regular Expressions), not all RegEx-powered search tools will recognize precisely the same expression patterns. Therefore, not all RegEx enhanced search-and-replace tools will respond as expected to the search string entered. The reader should not lose hope, however, for the differences tend to be subtle when compared to the similarities. For example, one of the RegEx patterns listed below illustrates how to use a particular tool for extracting separate databases from a complete MySQL server database backup. The syntax, as shown in the example, uses a backslash character for escaping the parenthesis used to define separate RegEx Atoms. That syntax dates back to the UNIX search tools, sed and grep. For the record– most tools I’ve used do not require escaping the atom encapsulating parenthesis in that manner, but I’ve listed it here as a reminder that, sometimes a failure to match the regular expression pattern is not due to the pattern itself, but the variations on PCRE present in different search tools. Should you encounter a peculiarity such as this, it’s best to consult the manual for the software first– if any time will be spent on debugging a regular expression pattern.

RegEx is Cool!

Like most people who are unfamiliar with Regular Expressions, I too found RegEx to be intimidating at first. The primary reason for their mystical difficulty, I believe, is because the syntax is unlike anything familiar to most people. The special characters and patterns are completely arbitrary, and therefore the RegEx newbie has no familiar ground on which to stand. With every step into RegEx, the newcomer is very aware of his footing, and must be very careful not to fall into the illusion of an abyss looming below! The key to survival in Regular Expressions, in the beginning, is to accept that learning the basics will require more memorization, and less apparent logic. Don’t let it scare you, but try to understand regex before memorizing the basics, like metacharacter, atom, and class syntax, and you may be doomed to frustration.
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My Regular Expression Solutions Library

I came across a few folders on an old hard drive where I had stored some Regular Expressions i found on-line. I realized that I had not yet begun a RegEx section here at NoviceNotes.Net, so i thought this would be the perfect opportunity to do so. I didn’t want to lose these notes, but I do want to wipe this old hard drive. So, I welcome you to share in the notes on Regular Expressions I intend to share here.

It’s all just syntax. To me it’s like spelling. Different words. Take what you need– it’s all just a collection of letters and words, so to speak. Good luck to you in your own RegEx Adventures!

Validate a Telephone Number – PHP preg_match() String:

This expression, written in PHP using the Perl Compatible RegEx (a.k.a. PCRE), built-in function preg_match() can be used to ensure that a user who encounters a telephone number submission form will indeed submit a valid telephone number. I have not put this expression into production, but i did try it. As far as i can tell, it does what it’s supposed to do! enjoy:


$phone = trim($phone);
if (!empty($phone) && !preg_match('/^\d{3}-\d{3}-\d{4}$/', $phone))
{
$errorCheck = TRUE;
$errorText = "Please use the 000-000-0000 format for a phone number.";
$valid = FALSE;
}


Extract Database Names from a MySQL Server Backup

If you ever find that you are unable to use phpMyAdmin to create your MySQL backup, I discovered the convenience, and apparently more failsafe method of backing up MySQL as one complete .sql file, like that which cPanel creates using the Backup Database option, or like that which is created my phpMyAdmin on Export.
If it is practical in your case to use the free-to-download, free-to-use (OEM) MySQL GUI Tool, MySQL Administrator (e.g. if you have a working copy of MySQL Administrator running on your system), instead of using phpMyAdmin for the database backup process, I suggest you try it next time. The resulting SQL file is nearly identical to that of the phpMyAdmin output we’re used to seeing, but for a few slight differences.

The following is the Regular Expression I used to search for the desired data within the MySQL Administrator SQL output; the complete localhost datbase backup created by the MySQL GUI Tool. The regular expression is shown here, enclosed in quotation marks, however the encapsulating quotation marks are NOT part of the actual Regular Expression itself:

 "^\(\-\-\sDatabase:\s\)\([\w]*\)"

Note: phpMyAdmin does not use precisely the

same syntax as MySQL Administrator to describe the database creation query to follow, but instead uses the following: “– Database: `database_name`”. Observe the character that phpMyAdmin uses as a delimiter encapsulates the database name here. Since that character can not be used in the filename, and the purpose of this RegEx search and replace operation is to make more efficient the effort of creating new .SQL files for each database extracted from the LOCALHOST .sql dump, the regular expression for a phpMyAdmin .SQL export will require the following modification, in the SEARCH string only:

"^\(\-\-\sDatabase:\s\)`\([\w]*\)`"

The “back-tick” characters have been placed outside of the second atom, so they are not included in the backreference.)

Using the .SQL file from MySQL Administrator, loaded in Notepad2 (a Scintilla-based editor), the replace syntax is as follows, again enclosed only here in quotes. do NOT use quotes if you wish to try this yourself or it won’t work properly.:

"\1\2\n-- \2.sql"

The same REPLACE string (previous sentence) should work without any changing for replacing the “find” results of the modified RegEx for phpMyAdmin (provided above, in parenthesis because it was added later) for use with phpMyAdmin.

Note: I used Notepad2 because of a unique “Select-To” feature in its Find and Replace dialogue. Instead of simply finding a phrase with my regular expression, Notepad2 can FIND one instance of the phrase, THEN “Select-to” the following instance of such a phrase, thereby selecting everything in between. As shown above, Notepad2 searched for “Create Schema”, a bit of text inserted by MySQL Administrator before each “CREATE DATABASE” expression, which marks the beginning of each new database. It was the regular expression finding this phrase accurately, and the very existence of the phrase which enabled me to make more efficient use of my time. I hope you find this to be useful! For more information on Notepad2, see http://www.flos-freeware.ch/ . I recommend you use the supplement file-manager software, mentioned in the “Notepad2″ documentation. “Metapad”, the file-browser, is simple to add to Notepad2.