![]() ![]() In regular expressions, the following characters will behave a bit oddly. This is a perfect opportunity to introduce the "metacharacters". The "Date" part of the regex makes sense, but what does the ".+" mean? What is the ^ at the beginning? If we omit these two characters, we will match the word "Date" 3 times, but we won't get the actual date information that we really want. When executed, this command will find and print out the three date lines. Set-Cookie: SIDCC=AN0-TYuz2RnQRkvCL-vKi53aZ9wq43igGogt5iPF1aveuchWK1_5cZsxzom9-PWiJjy8Sk7bvgY expires=Sun, 1 21:46:36 GMT path=/ domain=. priority=high Set-Cookie: SIDCC=AN0-TYsHoOeMCDEAZfNd9umwLDXDEHqyGfAImuc08v4h2e1B1hSKxGQAq7iVt0xFlQKLzVlgSTM expires=Sun, 1 21:44:38 GMT path=/ domain=. priority=high Strict-Transport-Security: max-age=31536000 Set-Cookie: SIDCC=AN0-TYtZ7bElYEE0wy8nAaXHUK_GRAsuZzNu7r5OhKVGKwr7a-m7ctz5IIHoZcvmh2s9xuDt0gc expires=Sun, 1 21:40:25 GMT path=/ domain=. priority=high If we activate the Perl regular expressions feature of grep, we can find this same word.Īlt-Svc: quic=":443" ma=2592000 v="44,43,39" ![]() It can also be done by a regular expression utility. What I just explained is called "literal text matching" and can be done using any text searching utility. This is an overly simplified explanation, but you can read more here if you're curious. ![]() If we reach the end of our search string without any errors, then we have matched the text.If there is a match, advance to the next letter in the search string and check to see if that matches the next character in the file.Read each character in the file one by one, seeing if that character matches the first character in our search string.If we were to write a text-matching program, it would roughly follow these steps: We all understand the basic concept of text matching, but sometimes don't take a moment to think about what it really is. Here are three different ways to use the same regular expression:Įnter fullscreen mode Exit fullscreen mode Let me first start by addressing the fact that there are many different versions of regular expressions. You may have to Google for help regarding specific use cases, but you will never have any confusion about regular expressions. Instead, I am going to teach you the methodology behind regular expressions that will give you a foundation to work with. Chances are, you will not need to use regular expressions on a daily basis, so I am not going to teach you all the nitty-gritty details that you will forget within a day. I have not yet explained what this syntax means, but essentially, we are searching for text that starts with "Book" and ends with 1 or more numbers.Ī more common example for regular expressions is searching large documents for email addresses or phone numbers or even validating user input in a web application. My regular expression was quite simple, and looked like this: ^Book+. Knowing that these new workbooks would always contain the word "Book" at the beginning, I was able to use a regular expression to identify them. Luckily, Excel opens new workbooks and names them "Book1", "Book2", "Book3", "Book4", etc. In each workbook, there was data that I needed to copy and paste into my main workbook, but in the code, I had no way of determining what the name of this new workbook was. As a result of this, the library would open up a new Excel workbook for every function call I made. The code of this external library was not available for me to see, and therefore, I had to use it with limited control. I recently wrote a script in Microsoft Excel VBA that executed commands from an external library. Let me give you an extremely practical example from my own work to explain. Regular expressions exist because a literal text searching program is sometimes not good enough. ![]() Despite this, there are only a few core concepts that one must understand about regular expressions that will then translate in the ability to use any flavor of regular expressions effectively. Sure, there are a lot of options and little details to learn regarding regular expressions, and on top of that, there are many different flavors of regular expressions (python, extended, rust, etc.). To me, regular expressions are often made far more complicated than they need to be. ![]()
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