bash - 无法让 expand_aliases 生效

Question

我无法让 expand_aliases 在 bash 中生效。我尝试了很多不同的方法，但没有任何效果。

这是一个简单的测试用例:

/bin/bash -c 'shopt -s expand_aliases; alias cdtmp="cd /tmp"; alias; cdtmp; pwd;'

输出:

$ /bin/bash -c 'shopt -s expand_aliases; alias cdtmp="cd /tmp"; alias; cdtmp; pwd;'
alias cdtmp='cd /tmp'
/bin/bash: cdtmp: command not found
/home/user

$ /bin/bash --version
GNU bash, version 3.2.25(1)-release (i686-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

(是的，我使用 shopt 而不是 bash 的 -O 选项，只是为了证明它已经完成。)

有什么想法吗？

Answer 1

别名在定义它们的同一行或同一函数中不可用。

来自 Bash 手册页:

       The rules concerning the definition and use  of  aliases  are  somewhat       confusing.   Bash  always  reads  at  least  one complete line of input       before executing any  of  the  commands  on  that  line.   Aliases  are       expanded  when  a command is read, not when it is executed.  Therefore,       an alias definition appearing on the same line as another command  does       not  take  effect  until  the next line of input is read.  The commands       following the alias definition on that line are not affected by the new       alias.   This  behavior  is  also an issue when functions are executed.       Aliases are expanded when a function definition is read, not  when  the       function  is  executed,  because a function definition is itself a com‐       pound command.  As a consequence, aliases defined in a function are not       available  until  after  that function is executed.  To be safe, always       put alias definitions on a separate line, and do not use alias in  com‐       pound commands.       For almost every purpose, aliases are superseded by shell functions.

Bash Reference Manual说

For almost every purpose, shell functions are preferred over aliases.

而不是上面的最后一句话 [强调我的]。我认为别名是命令行的一种便利，而不是应该在脚本中使用的东西(包括那些仅由 bash -c 单行代码组成的脚本)。