How is ではなく formed?

Question

この女の人はペンチではなく、ハンマーを使っています。

I believe the sentence means

The woman is using a hammer, not a pliers.

But I couldn't understand ではなく, how is this structure formed?

Answer 1

• で: The continuative form of the copula だ.
• は: The topic/contrast marker は, which is optional but is usually placed here. では can be contracted to じゃ in casual settings.
• なく: The continuative form of ない.
• (て): なく can be followed by an optional て. In casual conversation て tends to be used, and in formal essays て tends to be dropped.

Put together this literally means "not being ～". Practically this can be used wherever a noun can be used in a sentence, and means "not ～ (but ～)". This can be used with adverbs, too.

• 彼ではなく私がやりました。　＝　彼じゃなくて私がやりました。
• 彼は壁を赤くではなく青く塗った。
• ゆっくりではなく、急いで来てください。