Question

我无法让expand_aliases在bash中生效。我尝试了很多不同的东西，没有任何作用。

以下是简单的测试用例：

/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，我正在使用shopt而不是-O选项进行bash，只是为了证明它正在完成。）

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       For almost every purpose, aliases are superseded by shell functions.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

对于几乎所有目的，shell 函数优先于而不是别名。

而不是[强调我的]上面的最后一句话。我认为别名是命令行的便利，而不是脚本中应该使用的东西（包括那些仅由bash -c单行组成的东西。）

Answer 2

我来晚了十年。您可以使用eval使别名cdtmp再次扩展。

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

将为您提供输出

alias cdtmp='cd /tmp'
/tmp

Answer 3

试试/bin/bash -O expand_aliases -c 'xx'

无法使expand_aliases生效

3 个答案: