Breakdown of Я искал его линейку в шкафу.
я
I
в
in / to (direction)
шкаф
cabinet / wardrobe
искать
to look for
Questions & Answers about Я искал его линейку в шкафу.
Why doesn't его change its ending to match линейку?
Его means "his" in this sentence. Unlike other possessive pronouns like мой (my) or наш (our), the 3rd person possessive pronouns (его, её, их) are indeclinable. This means they never change their form, regardless of the gender, number, or case of the noun they describe. So, even though линейку is feminine and in the accusative case, его stays exactly the same.
Why does шкаф end in -у here (в шкафу) instead of the usual prepositional ending -е?
Шкаф belongs to a small group of short, single-syllable masculine nouns that take a special locative ending -у (which is always stressed) when answering the question "where?" after the prepositions в or на. Other common words you might remember in this group are лес (в лесу - in the forest) and пол (на полу - on the floor).
Why is линейку in the accusative case?
It is the direct object of the verb искал (was looking for). Because the action of searching is happening directly to the ruler, the feminine noun линейка changes its -а ending to -у to form the accusative case.
Why do we use the imperfective verb here instead of a perfective one?