bash 非贪婪匹配使用 ? 用 grep
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Non greedy matching using ? with grep
提问by Sven Richter
I'm writing a bash script which analyses a html file and
I want to get the content of each single <tr>...</tr>. So my command looks like:
我正在编写一个 bash 脚本来分析一个 html 文件，我想获取每个<tr>...</tr>. 所以我的命令看起来像：
$ tr -d \012 < price.html | grep -oE '<tr>.*?</tr>'
But it seems that grepgives me the result of:
但似乎grep给了我以下结果：
$ tr -d \012 < price.html | grep -oE '<tr>.*</tr>'
How can I make .*non-greedy?
我怎样才能.*不贪婪？
回答by Chris Seymour
If you have GNU Grepyou can use -Pto make the match non-greedy:
如果你有GNU Grep你可以-P用来使匹配非贪婪：
$ tr -d \012 < price.html | grep -Po '<tr>.*?</tr>'
The -Poption enables Perl Compliant Regular Expression (PCRE)which is needed for non-greedy matching with ?as Basic Regular Expression (BRE)and Extended Regular Expression (ERE)do not support it.
该-P选项启用非贪婪匹配所需的Perl 兼容正则表达式(PCRE)，?因为基本正则表达式(BRE)和扩展正则表达式(ERE)不支持它。
If you are using -Pyou could also use look aroundsto avoid printing the tags in the match like so:
如果您正在使用，-P您还可以使用环视来避免在匹配中打印标签，如下所示：
$ tr -d \012 < price.html | grep -Po '(?<=<tr>).*?(?=</tr>)'
If you don't have GNU grepand the HTML is well formed you could just do:
如果您没有GNU grep并且 HTML 格式良好，您可以这样做：
$ tr -d \012 < price.html | grep -o '<tr>[^<]*</tr>'
Note: The above example won't work with nested tags within <tr>.
注意：上面的示例不适用于<tr>.
回答by tripleee
Non-greedy matching is not part of the Extended Regular Expression syntax supported by grep -E. Use grep -Pinstead if you have that, or switch to Perl / Python / Ruby / what have you. (Oh, and pcregrep.)
非贪婪匹配不是grep -E. grep -P如果你有，请改用，或者切换到 Perl/Python/Ruby/你有什么。（哦，还有pcregrep。）
Of course, if you really mean
当然，如果你真的想说
<tr>[^<>]*</tr>
you should say that instead; then plain old grepwill work fine.
你应该这样说；那么普通的旧的grep就可以正常工作。
You could (tediously) extend the regex to accept nested tags which are not <tr>but of course, it's better to use a proper HTML parser than spend a lot of time rediscovering why regular expressions are not the right tool for this.
您可以（乏味地）扩展正则表达式以接受嵌套标签，<tr>但当然，最好使用适当的 HTML 解析器，而不是花费大量时间重新发现为什么正则表达式不是正确的工具。
回答by ThisSuitIsBlackNot
.*?is a Perl regular expression. Change your grepto
.*?是一个 Perl 正则表达式。改变你grep的
grep -oP '<tr>.*?</tr>'
回答by Fredrik Pihl
Try perl-style-regexp
试试 perl-style-regexp
$ grep -Po '<tr>.*?</tr>' input
<tr>stuff</tr>
<tr>more stuff</tr>
