There is this line in a shell script i have seen:
在我看到的shell脚本中有这一行:
grep -e ERROR ${LOG_DIR_PATH}/${LOG_NAME} > /dev/null
if [ $? -eq 0 ]
3 个解决方案
#1
32
It's checking the return value ($?) of grep. In this case it's comparing it to 0 (success).
它检查grep的返回值($?)。在本例中，它将其与0(成功)进行比较。
Usually when you see something like this (checking the return value of grep) it's checking to see whether the particular string was detected. Although the redirect to /dev/null isn't necessary, the same thing can be accomplished using -q.
通常，当您看到这样的东西(检查grep的返回值)时，它会检查是否检测到特定的字符串。尽管重定向到/dev/null并不是必需的，但是使用-q可以完成同样的事情。
#2
26
$? is the exit status of the most recently-executed command; by convention, 0 means success and anything else indicates failure. That line is testing whether the grep command succeeded.
$ ?是最近执行的命令的退出状态;按照惯例，0表示成功，其他任何表示失败。这一行正在测试grep命令是否成功。
The grep manpage states:
grep从状态:
The exit status is 0 if selected lines are found, and 1 if not found. If an error occurred the exit status is 2. (Note: POSIX error handling code should check for '2' or greater.)
如果找到选定的行，退出状态为0，如果没有找到，则为1。如果出现错误，退出状态为2。(注:POSIX错误处理代码应该检查“2”或更大。)
So in this case it's checking whether any ERROR lines were found.
在本例中，它检查是否找到了错误行。
#3
2
It is an extremely overused way to check for the success/failure of a command. Typically, the code snippet you give would be refactored as:
它是检查命令的成功/失败的一种极其过度使用的方法。通常，您给出的代码片段将被重构为:
if grep -e ERROR ${LOG_DIR_PATH}/${LOG_NAME} > /dev/null; then
...
fi
(Although you can use 'grep -q' in some instances instead of redirecting to /dev/null, doing so is not portable. Many implementations of grep do not support the -q option, so your script to fail if you use it.)
(尽管您可以在某些实例中使用“grep -q”，而不是重定向到/dev/null，这样做是不可移植的。grep的许多实现不支持-q选项，因此如果您使用它，您的脚本就会失败。
#1
32
It's checking the return value ($?) of grep. In this case it's comparing it to 0 (success).
它检查grep的返回值($?)。在本例中，它将其与0(成功)进行比较。
Usually when you see something like this (checking the return value of grep) it's checking to see whether the particular string was detected. Although the redirect to /dev/null isn't necessary, the same thing can be accomplished using -q.
通常，当您看到这样的东西(检查grep的返回值)时，它会检查是否检测到特定的字符串。尽管重定向到/dev/null并不是必需的，但是使用-q可以完成同样的事情。
#2
26
$? is the exit status of the most recently-executed command; by convention, 0 means success and anything else indicates failure. That line is testing whether the grep command succeeded.
$ ?是最近执行的命令的退出状态;按照惯例，0表示成功，其他任何表示失败。这一行正在测试grep命令是否成功。
The grep manpage states:
grep从状态:
The exit status is 0 if selected lines are found, and 1 if not found. If an error occurred the exit status is 2. (Note: POSIX error handling code should check for '2' or greater.)
如果找到选定的行，退出状态为0，如果没有找到，则为1。如果出现错误，退出状态为2。(注:POSIX错误处理代码应该检查“2”或更大。)
So in this case it's checking whether any ERROR lines were found.
在本例中，它检查是否找到了错误行。
#3
2
It is an extremely overused way to check for the success/failure of a command. Typically, the code snippet you give would be refactored as:
它是检查命令的成功/失败的一种极其过度使用的方法。通常，您给出的代码片段将被重构为:
if grep -e ERROR ${LOG_DIR_PATH}/${LOG_NAME} > /dev/null; then
...
fi
(Although you can use 'grep -q' in some instances instead of redirecting to /dev/null, doing so is not portable. Many implementations of grep do not support the -q option, so your script to fail if you use it.)
(尽管您可以在某些实例中使用“grep -q”，而不是重定向到/dev/null，这样做是不可移植的。grep的许多实现不支持-q选项，因此如果您使用它，您的脚本就会失败。