答案1
它是一个保留字。从man bash
:
RESERVED WORDS Reserved words are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted and either the first word of a simple command (see SHELL GRAMMAR below) or the third word of a case or for command: ! case coproc do done elif else esac fi for function if in select then until while { } time [[ ]]