Bash 脚本 - 在脚本中执行和 grep 命令
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1638503/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Bash scripting - execute and grep command inside script
提问by geord
Okay, so I'm learning Bash, and there's that exercise;
好的，所以我正在学习 Bash，还有那个练习；
"Write a script that checks every ten seconds if the user 'user000' is logged in."
“编写一个脚本，每 10 秒检查一次用户 'user000' 是否已登录。”
My idea is to grepa who, but I don't know how to incorporate this into a script. I tried things like
我的想法是grepa who，但我不知道如何将其合并到脚本中。我试过这样的事情
if [ `who | grep "user000"` ] then things
but it returns the matched lines with grep, not true/false.
但它用grep 返回匹配的行，而不是真/假。
回答by chaos
You want grep -q. That's "quiet mode"; just sets status based on whether there were any matches, doesn't output anything. So:
你要grep -q。那是“安静模式”；只是根据是否有任何匹配来设置状态，不输出任何内容。所以：
if who | grep -q "user000"; then things; fi
回答by DVK
You can do
你可以做
who | grep "user000" > /dev/null 2>&1
# You can use "-q" option of grep instead of redirecting to /dev/null
# if your grep support it. Mine does not.
if [ "$?" -eq "0" ]
then ...
This uses $? - a Shell variable which stores the return/exit code of the last command that was exected. grepexits with return code "0" on success and non-zero on failure (e.g. no lines found returns "1" ) - a typical arrangement for a Unix command, by the way.
这使用 $? - 一个 Shell 变量，用于存储执行的最后一个命令的返回/退出代码。grep成功退出时返回代码“0”，失败时返回非零（例如，找不到行返回“1”）——顺便说一下，这是 Unix 命令的典型安排。
回答by Paused until further notice.
If you're testing the exit code of a pipe or command in a ifor while, you can leave off the square brackets and backticks (you should use $()instead of backticks anyway):
如果你在一个测试管或命令的退出代码if或者while，可以去掉方括号和反引号（你应该使用$()反正不是反引号的）：
if who | grep "user000" > /dev/null 2>&1
then
things-to-do
fi
回答by Walter Mundt
Most answers have the right idea, but really you want to drop all output from grep, including errors. Also, a semicolon is required after the ] for an if:
大多数答案都有正确的想法，但实际上您想删除 grep 的所有输出，包括错误。此外，if 的 ] 后面需要一个分号：
if who | grep 'user000' >/dev/null 2>&1; then
do things
fi
If you are using GNU grep, you can use the -sand -qoptions instead:
如果您使用的是 GNU grep，则可以使用-s和-q选项：
if who | grep -sq 'user000'; then
do things
fi
EDIT: dropped brackets; if only needs brackets for comparison ops
编辑：删除括号；如果只需要括号进行比较操作
回答by the_mandrill
It's probably not the most elegant incantation, but I tend to use:
这可能不是最优雅的咒语，但我倾向于使用：
if [ `who | grep "user000" | wc -l` = "1" ]; then ....
