Linux Bash shell 'if' 语句比较来自不同命令的输出
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/7850631/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Bash shell 'if' statement comparing outputs from different commands
提问by bikerben
Using an adapted example given to me by Sam Rubywhich I have tweaked so I can show what I'm trying to achieve.
使用Sam Ruby 给我的一个改编示例，我对其进行了调整，以便我可以展示我想要实现的目标。
app1=$(someapp -flag | grep usefulstuff | cut -c 5-10)
if [$app1 = (someapptwo -flag | grep usefulstuff | cut -c 20-25)]; then
mkdir IPFolder-1
elif ...blah blah
fi
Can I use grep as show above or am I barking up the wrong tree? or should it look a little some thing like this:
我可以使用上面显示的 grep 还是我吠错了树？或者它应该看起来像这样：
app1=$(someapp -flag | grep usefulstuff | cut -c 5-10)
app2=$(someapptwo -flag | grep usefulstuff | cut -c 20-25)
if [$app1 = $app2]; then
mkdir IPFolder-1
elif ...blah blah
fi
回答by milancurcic
You need to refer to the value of your expression by prepending a $:
您需要在前面加上 $ 来引用表达式的值：
...
if [ "$app1" = "$(someapptwo -flag | grep usefulstuff | cut -c 20-25)" ]; then
...
回答by Jonathan Leffler
At least in other shells, you need to be a lot more careful with spaces; the square bracket is a command name and needs to be separated from previous and following words. You also need (again in classic shells for certain) to embed the variables in double quotes:
至少在其他 shell 中，您需要对空格更加小心；方括号是命令名，需要与前后单词分开。您还需要（再次在经典 shell 中）将变量嵌入双引号中：
app1=$(someapp -flag | grep usefulstuff | cut -c 5-10)
if [ "$app1" = "$(someapptwo -flag | grep usefulstuff | cut -c 20-25)" ]
then mkdir IPFolder-1
elif ...blah blah
then : do this instead...
fi
You could do it all in one line (well, two because I avoid the horizontal scrollbar whenever possible):
您可以在一行中完成所有操作（好吧，两行是因为我尽可能避免使用水平滚动条）：
if [ "$(someapp -flag | grep usefulstuff | cut -c 5-10)" = \
"$(someapptwo -flag | grep usefulstuff | cut -c 20-25)" ]
then mkdir IPFolder-1
elif ...blah blah
then : do this instead...
fi
Or you could do it with two separate command captures:
或者您可以使用两个单独的命令捕获来完成：
app1=$(someapp -flag | grep usefulstuff | cut -c 5-10)
app2=$(someapptwo -flag | grep usefulstuff | cut -c 20-25)
if [ "$app1" = "$app2" ]
then mkdir IPFolder-1
elif ...blah blah
then : do this instead...
fi
Update:Some extra quotes added. It would be possible to quote the assignments too:
更新：添加了一些额外的引号。也可以引用作业：
app1="$(someapp -flag | grep usefulstuff | cut -c 5-10)"
No harm would be done; it isn't strictly necessary with bash(but it may well have been necessary with archaic Bourne shell).
不会造成任何伤害；它不是绝对必要的bash（但对于古老的 Bourne shell 可能是必要的）。
