Greedy expressions in Regex.mp4

 

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Greedy Expressions in Regular Expressions (Regex)

Greedy expressions are the default behavior in most regex engines.
They try to match as much text as possible while still allowing the overall pattern to succeed.

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What does “greedy” mean?

When a regex uses a quantifier like:

• * → 0 or more times

• + → 1 or more times

• ? → 0 or 1 time

• {m,n} → between m and n times

…the regex engine will expand the match to the maximum length it can.

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Simple Example

Text

aaaa

Regex

a+

Match

aaaa

👉 The + quantifier is greedy, so it matches all four a characters instead of stopping early.

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Greedy vs Expected Result

Text

"<title>Regex</title>"

Regex

<.*>

Matched result

<title>Regex</title>

Why?

• .* means “any character, zero or more times”

• Being greedy, it stretches from the first < to the last >

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Another Clear Example

Text

abc123xyz456

Regex

.*\d+

Match

abc123xyz456

✔ .* first consumes everything
✔ Then it backtracks just enough to allow \d+ to match the final digits

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Common Greedy Quantifiers

Quantifier	Meaning	Greedy Behavior
*	0 or more	Matches as much as possible
+	1 or more	Matches the longest sequence
?	0 or 1	Prefers 1 if possible
{m,n}	Range	Matches up to n times

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Visual Understanding

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Why Greedy Matching Matters

Greedy expressions can:

• Accidentally match too much

• Cause unexpected results when parsing HTML, XML, or logs

• Require careful pattern design

Example issue

<.*>

❌ Too broad
✔ Often needs constraints or lazy quantifiers (like .*?)

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Quick Tip

If your regex matches more than you expect,
it’s probably because a greedy quantifier is consuming too much.

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Summary

• Greedy expressions are default in regex

• They always match the longest possible string

• Quantifiers like *, +, ?, {m,n} are greedy by nature

• Understanding greedy behavior helps avoid over-matching bugs