Linux 如果 [[ $? -ne 0 ]]; .ksh 中的意思
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What does if [[ $? -ne 0 ]]; mean in .ksh
提问by Rahul sawant
I have a following piece of code that says if everything is executed mail a person if it fails mail the person with a error message.
我有以下一段代码，它说如果一切都执行了，如果失败，则向一个人发送邮件，并向该人发送错误消息。
if [[ $? -ne 0 ]]; then
mailx -s" could not PreProcess files" [email protected]
else
mailx -s" PreProcessed files" [email protected]
fi
done
I am new to linux coding I want to understand what if [[ $? -ne 0 ]];means
我是 linux 编码的新手，我想了解这if [[ $? -ne 0 ]];意味着什么
采纳答案by bishop
Breaking it down, simple terms:
分解它，简单的术语：
[[ and ]]
... signifies a test is being made for truthiness.
... 表示正在对真实性进行测试。
$?
... is a variable holding the exit code of the last run command.
... 是保存上次运行命令的退出代码的变量。
-ne 0
... checks that the thing on the left ($?) is "not equal" to "zero". In UNIX, a command that exits with zero succeeded, while an exit with any other value (1, 2, 3... up to 255) is a failure.
... 检查左侧 ( $?) 的内容是否“不等于”为“零”。在 UNIX 中，以零退出的命令成功，而以任何其他值（1、2、3...最多 255）退出的命令是失败的。
回答by anubhava
if [[ $? -ne 0 ]];
Is checking return code of immediately previous this if condition.
正在检查此 if 条件之前的返回码。
$?means return code$? -ne 0means previous command returned an error since 0 is considered success
$?表示返回码$? -ne 0表示前一个命令返回错误，因为 0 被认为是成功
回答by Claudio
If the previous command returned an error return code.
如果前一个命令返回错误返回码。
回答by William Pursell
Presumably, the snippet is part of code that looks something like:
据推测，该片段是代码的一部分，如下所示：
for var in list of words; do
cmd $var
if [[ $? -ne 0 ]]; then
mailx -s" could not PreProcess files" [email protected]
else
mailx -s" PreProcessed files" [email protected]
fi
done
Which could (and should) be re-written more simply as:
可以（并且应该）更简单地重写为：
for var in list of words; do
if ! cmd $var; then
message="could not PreProcess files"
else
message="PreProcessed files
fi
mailx -s" $message" [email protected]
done
The [[ $? -ne 0 ]]clause is a hackish way to check the return value of cmd, but it is almost always unnecessary to check $?explicitly. Code is nearly always cleaner if you let the shell do the check by invoking the command in the if clause.
该[[ $? -ne 0 ]]子句是检查 的返回值的一种骇人听闻的方式cmd，但几乎总是没有必要$?显式检查。如果让 shell 通过调用 if 子句中的命令来进行检查，代码几乎总是更干净。
