如何在tcsh Shell中检查变量是否为空？ [英] How can I check if a variable is empty or not in tcsh Shell?

问题描述

如果我必须检查bash shell中变量是否为空，则可以使用以下脚本进行检查：

IF I have to check that if a variable is empty or not for that in bash shell i can check with the following script:

if [ -z "$1" ] 
then
    echo "variable is empty"
else 
    echo "variable contains $1"
fi

但是我需要将其转换为tcsh shell。

But I need to convert it into tcsh shell.

推荐答案

关于使用 tcsh / csh 的标准警告适用（不适用由于其固有的限制，因此将其用于脚本 ，但翻译如下：

The standard warnings regarding use of tcsh/csh apply (don't use it for scripting, due to its inherent limitations), but here's the translation:

if ( "$1" == "" ) then      # parentheses not strictly needed in this simple case
    echo "variable is empty"
else 
    echo "variable contains $1"
endif

但是请注意，如果要使用任意变量名而不是 $ 1 中，如果尚未定义该变量，则语句会中断（而 $ 1 始终是定义的，即使未设置也是如此）。

Note, though, that if you were to use an arbitrary variable name rather than $1 in the above, the statement would break if that variable weren't defined yet (whereas $1 is always defined, even if unset).

要计划变量的情况，例如 $ var ，可能未定义，这很棘手：

To plan for the case where a variable, say $var, may not be defined, it gets tricky:

if (! $?var) then       
  echo "variable is undefined"
else
  if ("$var" == "")  then
      echo "variable is empty"
  else 
      echo "variable contains $var"
  endif
endif

嵌套 if 是必需的，以避免破坏脚本，因为 tcsh 显然不会短路（如果分支的条件将被评估，即使输入 分支；同样，& 和 || 表达式似乎总是被评估-至少在使用未定义变量时适用。）

The nested ifs are required to avoid breaking the script, as tcsh apparently doesn't short-circuit (an else if branch's conditional will get evaluated even if the if branch is entered; similarly, both sides of && and || expressions are seemingly always evaluated - this applies at least with respect to use of undefined variables).

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