true命令啥都不做，只設置退出碼為0。 在linux底下，每個程序執(zhí)行完畢都會返回一個退出碼給調(diào)用者，一般情況下0表示成功，其他值表明有問題，當然某些程序的退出碼有特殊含義。有些shell下true可能是個內(nèi)建命令，至少bash下是。（do nothing, successfully。Exit with a status code indicating success. NOTE: your shell may have its own version of true, which usually supersedes the version described here. ?Please refer to your shell’s documentation for details about the options it supports.）
