Bash 中预期的一元运算符
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原文地址: http://stackoverflow.com/questions/22798333/
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Unary operator expected in Bash
提问by Paolo
I've seen questions regarding the same issue, but all of them are about strings. How about integers, why am I getting the "unary operator expected" error?
我看过有关同一问题的问题，但所有问题都与字符串有关。整数怎么样，为什么我会收到“预期的一元运算符”错误？
if [ $(date +%k%M) -ge ${!BLOCK1FRAN} ] ; then whatever ; fi
回答by alvits
You are using indirection. If the variable ${BLOCK1FRAN}points to an empty variable, you'll get the error message. Make sure that the variable pointed by ${BLOCK1FRAN}contains valid numeric value.
您正在使用间接。如果变量${BLOCK1FRAN}指向一个空变量，您将收到错误消息。确保指向的变量${BLOCK1FRAN}包含有效的数值。
If you want empty string and non numeric values to be evaluated as zero 0use the following syntax.
如果您希望将空字符串和非数字值计算为零，请0使用以下语法。
if [[ $(date +%k%M) -ge ${!BLOCK1FRAN} ]]; then whatever ; fi
回答by that other guy
Looks good to me. Are you sure you've set BLOCK1FRAN correctly?
在我看来很好。你确定你已经正确设置了 BLOCK1FRAN 吗？
$ whatever() { echo "it works"; }
$ foo=42
$ BLOCK1FRAN=foo
$ if [ $(date +%k%M) -ge ${!BLOCK1FRAN} ] ; then whatever ; fi
it works
