bash 将输出存储在变量中并在命令中使用变量
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Store output in variable & use variable in command
提问by ojhawkins
I am trying to run a command and store it in a variable.
我正在尝试运行一个命令并将其存储在一个变量中。
length=`last | grep foouser | wc -l`
It works fine but when I add a variable to the command it breaks.
它工作正常，但是当我向命令添加变量时，它会中断。
value=
length=`last | grep $value | wc -l`
How can I get this second example to work by acceptomg a variable?
如何通过接受变量来使第二个示例工作？
回答by Benoit
You should quote your variables properly. If they contain spaces your script might break:
您应该正确引用您的变量。如果它们包含空格，您的脚本可能会中断：
value=""
length="$(last | grep "$value" | wc -l)"
回答by glenn Hymanman
You don't actually need wc:
你实际上并不需要wc：
length=$(last | grep -c "$value")
You could improve the variable names
您可以改进变量名称
num_logins=$(last | grep -c "$username")
