Gsub and sub for replacement in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sub method do in Ruby?

The sub method replaces the first occurrence of a pattern in a string with a specified replacement.

beginner

How is gsub different from sub in Ruby?

gsub replaces all occurrences of a pattern in a string, while sub replaces only the first occurrence.

beginner

Example: What is the result of "hello world".sub("l", "x")?

It returns "hexlo world" because only the first l is replaced by x.

beginner

Example: What is the result of "hello world".gsub("l", "x")?

It returns "hexxo worxd" because all l characters are replaced by x.

intermediate

Can sub and gsub accept a block for dynamic replacement?

Yes, both methods can take a block to compute the replacement dynamically for each match.

Which Ruby method replaces only the first match in a string?

A replace

B gsub

C sub

D match

sub replaces only the first occurrence, while gsub replaces all.

What will "banana".gsub("a", "o") return?

A "bonono"

B "banana"

C "bonana"

D "banano"

All a characters are replaced by o, so the result is "bonono".

Which method can take a block to customize replacements?

A gsub only

B both sub and gsub

C sub only

D neither

Both sub and gsub can accept a block for dynamic replacement.

What does "abcabc".sub(/a/, "x") return?

A "xbcxbc"

B "xxcabc"

C "abcabc"

D "xbcabc"

sub replaces only the first a, so the result is "xbcabc".

If you want to replace all digits in a string with "#", which method do you use?

A gsub

B scan

C match

D sub

gsub replaces all matches, so it is used to replace all digits.

Explain the difference between sub and gsub in Ruby.

Think about how many matches each method changes.

Describe how you can use a block with gsub to replace matches dynamically.

Blocks let you decide replacement based on the match.