Why can't Regular Expressions use keywords instead of characters?

Question

Okay, I barely understand RegEx basics, but why couldn\'t they design it to use keywords (like SQL) instead of some cryptic wildcard characters and symbols?

Is it for pe

Answer 1

Regular expressions have a mathematical (actually, language theory) background and are coded somewhat like a mathematical formula. You can define them by a set of rules, for example

• every character is a regular expression, representing itself
• if a and b are regular expressions, then a?, a|b and ab are regular expressions, too
• ...

Using a keyword-based language would be a great burden for simple regular expressions. Most of the time, you will just use a simple text string as search pattern:

grep -R 'main' *.c

Or maybe very simple patterns:

grep -c ':-[)(]' seidl.txt

Once you get used to regular expressions, this syntax is very clear and precise. In more complicated situations you will probably use something else since a large regular expression is obviously hard to read.