How can you express that you deleted a file unintentionally using "by mistake"?

The expression "I deleted the file by mistake" clearly conveys that the action of deleting the file was unintentional. The phrase "by mistake" explicitly indicates that the deletion was not planned, which aligns perfectly with the request to express unintentionality.

This choice is direct and simple, making it an effective way to communicate the idea that an error occurred during the deletion process. Other options share similar meanings but may differ slightly in tone or structure. For instance, "I accidentally deleted the file" suggests the same outcome but uses "accidentally," which while synonymous, is not the phrase requested. "I mistakenly deleted the file" uses "mistakenly," which somewhat alters the nuance, as it places focus on the mistake rather than the unintentional nature of the action itself. Lastly, "I had deleted the file by mistake" implies a past perfect tense, which may not be necessary for the situation being described, adding complexity without enhancing clarity. Thus, the first option remains the most straightforward and relevant answer to the original query.