具有前瞻模式的 grep 命令不选择任何内容 [英] grep command with a lookahead pattern does not select anything

问题描述

我试图使用以下 grep 命令:

I was trying to use the following grep command:

grep '(.*)(?=(png|html|jpg|js|css)(?:s*))(png|html|jpg|js|css.*s)' file

文件包含以下内容:

 http://manage.bostonglobe.com/GiftTheGlobe/LandingPage.html
 https://manage.bostonglobe.com/cs/mc/login.aspx?p1=BGFooter
 https://www.bostonglobe.com/bgcs
 /newsletters?p1=BGFooter_Newsletters
 https://bostonglobe.custhelp.com/app/home?p1=BGFooter
 https://bostonglobe.custhelp.com/app/answers/list?p1=BGFooter
 /tools/help/stafflist?p1=BGFooter
 https://www.bostonglobemedia.com/
 https://manage.bostonglobe.com/Order/newspaper/Newspaper.aspx
 https://www.facebook.com/globe
 https://twitter.com/#!/BostonGlobe
 https://plus.google.com/108227564341535363126/about
 https://epaper.bostonglobe.com/launch.aspx?pbid=2c60291d-c20c-4780-9829-     b3d9a12687cf
 http://nieonline.com/bostonglobe/
 https://secure.pqarchiver.com/boston-sub/no_default.html?ss=1&url=%2Fboston-sub%2Fadvancedsearch.html
 /tools/help/privacy?p1=BGFooter
 /tools/help/terms-service?p1=BGFooter
 /termsofpurchase?p1=BGFooter
 https://www.bostonglobemedia.com/careers
 /css/globe-print.css?v=19256I1935
 //meter.bostonglobe.com/css/style.css
 /css/globe-print.css?v=19256I1935
 //cdn.blueconic.net/bostonglobemedia.js
 /js/lib/rwd-images.js,lib/respond.min.js,lib/modernizr.custom.min.js,globe-          define.js,globe-controller.js?v=19256I1935
 data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==
 /js/lib/jquery.js,lib/lo-dash-custom-2.4.1.js,lib/a9.js,lib/pb.js,dist/ad-     init.js,globe-newsletter.js,globe-profile-page.js,dist/globe-topic-nav.js,dist/rakuten.js?v=19256I1935
 //dc8xl0ndzn2cb.cloudfront.net/js/bostonglobe/v0/keywee.min.js

出于某种原因，它没有从该文件中选择任何内容，我尝试了不同的标志，但似乎无法弄清楚出了什么问题

For some reason it doesn't select anything from that file, Ive tried different flags but cant seem to figure out whats wrong

推荐答案

您正在将 PCRE 正则表达式与 POSIX BRE 引擎一起使用，该引擎是默认的 grep 引擎.

You are using a PCRE regex with the POSIX BRE engine that is default grep engine.

要使这些模式起作用，您应该使用 -P 选项(在 GNU grep 中可用):

To make those patterns work, you should use -P option (available in GNU grep):

grep -P 'YOUR_PCRE_PATTERN'
     ^^

要开发和测试 PCRE 模式，通常推荐使用众所周知的 regex101.com.

To develop and test PCRE patterns, a well-known regex101.com is usually recommended.

请注意，在 Mac OS 上，您可以安装GNU grep 通过 brew.

Note that on Mac OS, you may install GNU grep via brew.

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