man truncate
shrink or extend the size of a file to the specified size
使い方（cheatコマンドから）
$ cheat truncate # To clear the contents from a file: truncate -s 0 file.txt # To truncate a file to 100 bytes: truncate -s 100 file.txt # To truncate a file to 100 KB: truncate -s 100K file.txt # (M, G, T, P, E, Z, and Y may be used in place of "K" as required.)
