String mutation and precise matching

The idea

Ruby strings are mutable objects. Assigning one string variable to another shares the object, while dup creates a separate outer object. Methods such as strip return transformed strings, and their bang counterparts generally modify the receiver. Do not assume every bang method has identical return behavior; some return nil when they make no change. Read the method’s contract before chaining through its result.

Validation should match the complete intended input, not merely find a suitable fragment somewhere inside it. Ruby regular-expression anchors \A and \z describe the absolute beginning and end of a string. This matters when input contains line breaks and line-oriented anchors would accept only one line. Keep a normalized comparison key separate from the original spelling when the interface should retain user-facing text.

raw="  Map "
alias_text=raw
clean=raw.strip
alias_text.replace("Grid")
puts raw
puts clean

Grid
Map

The alias mutates the original object, while strip already produced a separate normalized value.