true命令啥都不做,只设置退出码为0。
在linux底下,每个程序执行完毕都会返回一个退出码给调用者,一般情况下0表示成功,其他值表明有问题,当然某些程序的退出码有特殊含义。有些shell下true可能是个内建命令,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.)
相对应的命令是false,也是啥都不干,但退出码设置为1。