bash 评估和字符串“返回”
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eval and string "return"
提问by MSC29
Edit: I'm creating a bash script to run Netezza queries.
编辑：我正在创建一个 bash 脚本来运行 Netezza 查询。
here's an example of what I have to do:
这是我必须做的一个例子：
nzsql -host localhost -port 123456 -d db -u usr -pw pwd -A -t -c "insert into TABLE (name,surname) values ('m','sc')"
and it should return
它应该返回
INSERT 0 1
What I need is retrieve the number "1" which means that 1 row was inserted.
我需要的是检索数字“1”，这意味着插入了 1 行。
For this, I'd need to retrieve the whole string "INSERT 0 1" and work on it.
为此，我需要检索整个字符串“INSERT 0 1”并对其进行处理。
according to http://www.enzeecommunity.com/thread/2423this should work:
根据http://www.enzeecommunity.com/thread/2423这应该有效：
cmnd_output=`nzsql -host $NZ_HOST -d $NZ_DATABASE -u $NZ_USER -pw $NZ_PASSWORD -A -t -c "insert into TEST values ('test 1')"`
But I can't get it to work with this: ($2 is right because when I run it from the terminal it works just fine)
但我无法让它工作：（$ 2 是正确的，因为当我从终端运行它时，它工作得很好）
cmd_out=`` or cmd_out=`""` or cmd_out="``" or cmd_out=`"''"`
cmd_out=$() or cmd_out="$()" or cmd_out=$("")
It tells me command not found... just like if there was a "string quote" problem with $2
它告诉我找不到命令……就像 $2 存在“字符串引用”问题一样
I've however managed to execute $2 with eval
然而，我设法用 eval 执行了 $2
eval ""
and it works great, the command $2 is executed just fine. But, I can't use eval in this case as I want to store in a variable that "INSERT 0 1".
它工作得很好，命令 $2 执行得很好。但是，在这种情况下我不能使用 eval，因为我想存储在“INSERT 0 1”的变量中。
回答by Marc B
A simple
一个简单的
variable_int=`$function '$arg1' '$arg2'`
without the eval won't do?
没有 eval 不行吗？
回答by bash-o-logist
To assign return values from functions to a shell variable, use command substitution
要将函数的返回值分配给 shell 变量，请使用命令替换
variable=$(function arg1 arg2)
Why do you need eval?
你为什么需要eval？
回答by Paul Rubel
When you run into a problem like this I find it's always very useful to run with the -x option, just change the top sh-bang line like so:
当您遇到这样的问题时，我发现使用 -x 选项运行总是非常有用，只需像这样更改顶部的 sh-bang 行：
#!/bin/bash -x
That'll print out each line as it's currently interpreted before executing it. You can see how your variables are being mangled and use that to fix the problem.
这将在执行之前打印出当前解释的每一行。您可以查看变量是如何被破坏的，并使用它来解决问题。
