语法错误：使用 Bash 时需要操作数
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Syntax error: operand expected when using Bash
提问by teutara
I have two arrays that I want to loop in. I construct those properly and before going into for loop, I do echo them to be sure everything is ok with arrays. But when I run the script, it outputs an error:
我有两个我想循环的数组。我正确地构造了它们，在进入 for 循环之前，我会回显它们以确保数组一切正常。但是当我运行脚本时，它输出一个错误：
l<=: syntax error: operand expected (error token is "<="
I consulted the mighty Google and I understood it suffers from the lack of the second variable, but I mentioned earlier I do echo the values and everything seems to be OK. Here is the snippet..
我咨询了强大的谷歌，我知道它缺乏第二个变量，但我之前提到过我确实回应了这些值，一切似乎都没问题。这是片段..
#!/bin/bash
k=0
#this loop is just for being sure array is loaded
while [[ $k -le ${#hitEnd[@]} ]]
do
echo "hitEnd is: ${hitEnd[k]} and hitStart is: ${hitStart[k]}"
# here outputs the values correct
k=$((k+1))
done
k=0
for ((l=${hitStart[k]};l<=${hitEnd[k]};l++)) ; do //this is error line..
let array[l]++
k=$((k+1))
done
The variables in the for loop are echoed correctly but for loop won't work.. where am I wrong?
for 循环中的变量正确回显，但 for 循环不起作用..我哪里错了？
#as gniourf_gniourf answered:
正如 gniourf_gniourf 回答的那样：
"... At some point, k will reach the value ${#hitEnd[@]}, and this is exactly when hitEnd[k] is not defined and expands to an empty string! Bang!"
“...在某个时候，k 将达到 ${#hitEnd[@]} 的值，而这正是当 hitEnd[k] 未定义并扩展为空字符串时！砰！”
meaning error output is displayed not at the beginning of the loop, but when k has a greater value than array's indices, pointing an index that array does not include...
这意味着错误输出不显示在循环的开头，但是当 k 的值大于数组的索引时，指向数组不包含的索引...
采纳答案by gniourf_gniourf
That's because at some point ${hitEnd[k]}expands to nothing (it is undefined). I get the same error with ((l<=)). You should write your forloop as:
那是因为在某些时候${hitEnd[k]}扩展为空（它是未定义的）。我遇到同样的错误((l<=))。您应该将for循环编写为：
k=0
for ((l=${hitStart[0]};k<${#hitEnd[@]} && l<=${hitEnd[k]};l++)); do
so as to always have an index kthat corresponds to a defined field in the array ${hitEnd[@]}.
以便始终具有k与数组中定义的字段相对应的索引${hitEnd[@]}。
Also, instead of
另外，代替
k=$((k+1))
you can just write
你可以写
((++k))
Done!
完毕！
Your script revised using better modern bash practice:
您的脚本使用更好的现代 bash 实践进行了修改：
#!/bin/bash
k=0
#this loop is just for being sure array is loaded
while ((k<=${#hitEnd[@]})); do
echo "hitEnd is: ${hitEnd[k]} and hitStart is: ${hitStart[k]}"
# here outputs the values correct
((++k))
done
k=0
for ((l=hitStart[0];k<${#hitEnd[@]} && l<=hitEnd[k];++l)); do
((++array[l]))
((++k))
done
Now, I'm not too sure the forloop does exactly what you want it to... Don't you mean this instead?
现在，我不太确定for循环完全按照您的意愿执行……您不是说这个吗？
#!/bin/bash
# define arrays hitStart[@] and hitEnd[@]...
# define array array[@]
#this loop is just for being sure array is loaded
for ((k=0;k<${#hitEnd[@]};++k)); do
echo "hitEnd is: ${hitEnd[k]} and hitStart is: ${hitStart[k]}"
# here outputs the values correct
((++k))
done
for ((k=0;k<${#hitEnd[@]};++k)); do
for ((l=hitStart[k];l<=hitEnd[k];++l)); do
((++array[l]))
done
done
回答by sampson-chen
A bit bandaid-y, but you rewrite your for-loop into a while loop:
有点创可贴，但您将 for 循环重写为 while 循环：
l="${hitStart[k]}"
while [[ "$l" -le "${hitEnd[k]}" ]]; do
let array[l]++
k=$((k+1))
l=$((l+1))
done
