Article Diary - General Knowledge Digest

8 Basics of Regular Expressions

Regular expressions have been something that I was scared of when I started coding as a serious stuff. The string literals puzzled me like anything. preg_match, preg_grep, preg_split, preg_replace etc have been something I always wanted to avoid. This is for you guys who find regular expressions tacky.

1. “^tech

Searches a string that starts with tech.

2. “logy$”

Searches for strings that ends up in logy.

3. “a*b”

Looks for a string that has either zero or more a’s but exactly one b following a. (eg. b, ab, aab, aaab, aaaaaaaaaaaaaaaaab etc.).

4. “a+b”

Same as a*b but only difference is that atleast one a should be there in the string unlike a*b which can overlook a. (eg. ab, aab,aaaaaaaaab etc).

5. “a?b”

In this case string might have either zero or a single a (eg. ab or b) only these two possibilities are there.

QUANTIFYING THE CHARACTERS

To quantify the characters into certain sets and utilize them we can use paranthesis().

6. “(abc)+def”

Matches a string which consists of pattern having abc either one or n times followed by def at the end.

LOGICAL OPERATORS [OR(|) & AND(.)]

7. “(a|b)*c”

A string of a and b that ends in a c.

To specify range of characters. For instance to match that in a password small-case character, you can specify the set as [a-z] or [A-Z] or [0-9].

8. “([a-z])|([A-Z])”

Searches for a pattern having either small-case or capital letters.
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