bash 在 ksh 中比较字符串的相等性
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Comparing strings for equality in ksh
提问by Vijay
i am testing with the shell script below:
我正在使用下面的 shell 脚本进行测试：
#!/bin/ksh -x
instance=`echo | cut -d= -f2`
if [ $instance == "ALL" ]
then
echo "strings matched \n"
fi
It's giving this error in the if condition:
它在 if 条件下给出了这个错误：
: ==: unknown test operator
is ==really not the correct syntax to use?
I am running on the command line as below
是==真的不使用正确的语法？我在命令行上运行如下
test_lsn_2 INSTANCE=ALL
Could anybody please suggest a solution. Thanks.
任何人都可以请提出解决方案。谢谢。
采纳答案by Alberto Zaccagni
I see that you are using ksh, but you added bash as a tag, do you accept a bash-related answer? Using bash you can do it in these ways:
我看到您正在使用 ksh，但是您添加了 bash 作为标签，您是否接受与 bash 相关的答案？使用 bash，您可以通过以下方式进行操作：
if [[ "$instance" == "ALL" ]]
if [ "$instance" = "ALL" ]
if [[ "$instance" -eq "ALL" ]]
See herefor more on that.
有关更多信息，请参见此处。
回答by Andre Miller
To compare strings you need a single =, not a double. And you should put it in double quotes in case the string is empty:
要比较字符串，您需要一个 =，而不是双。如果字符串为空，您应该将其放在双引号中：
if [ "$instance" = "ALL" ]
then
echo "strings matched \n"
fi
回答by Aaron Digulla
Try
尝试
if [ "$instance" = "ALL" ]; then
There were several mistakes:
有几个错误：
You need double quotes around the variable to protect against the (unlikely) case that it's empty. In this case, the shell would see
if [ = "ALL" ]; thenwhich isn't valid.Equals in the shell uses a single
=(there is no way to assign a value in anifin the shell).
您需要在变量周围加上双引号以防止（不太可能）它为空的情况。在这种情况下，shell 会看到
if [ = "ALL" ]; then哪个无效。Equals 在 shell 中使用单个
=（在 shell中无法在 anif中赋值）。
回答by ghostdog74
totest=
case "$totest" in
"ALL" ) echo "ok" ;;
* ) echo "not ok" ;;
esac
回答by soulmerge
I'va already answered a similar question. Basically the operator you need is =(not ==) and the syntax breaks if your variable is empty (i.e. it becomes if [ = ALL]). Have a look at the other answerfor details.
我已经回答了一个类似的问题。基本上，您需要的运算符是=(not ==)，如果您的变量为空（即变为if [ = ALL]），则语法会中断。详情请查看其他答案。
