{"id":22,"date":"2008-12-25T22:46:57","date_gmt":"2008-12-26T02:46:57","guid":{"rendered":"http:\/\/adamrosenfield.com\/blog\/?p=22"},"modified":"2008-12-25T22:46:57","modified_gmt":"2008-12-26T02:46:57","slug":"not-your-average-regex-find-and-replace","status":"publish","type":"post","link":"http:\/\/adamrosenfield.com\/blog\/2008\/12\/25\/not-your-average-regex-find-and-replace\/","title":{"rendered":"Not your average regex find-and-replace"},"content":{"rendered":"

I was reading through some of the Coding Horror<\/a> archives, and came across this post<\/a> examining Microsoft Visual Studio’s use of regular expressions in its find-and-replace dialog. Visual Studio has support for all of the usual regex constructs but throws in a lot of its own quirky constructs too. I suppose they could be useful if you learned to use them.<\/p>\n

But this post isn’t about Visual Studio. Jeff’s post contained an intriguing link to Steve Yegge’s blog<\/a>, where Steve goes over some of the new features in Emacs 22. And despite my being a long-time emacs user, I was pleasantly surprised to learn that you can use elisp with find-and-replace<\/b>. <\/p>\n

Now at first, this may not seem like a big deal. You can do a lot with a plain vanilla find-and-replace (M-x replace-string<\/code> and M-x query-replace<\/code> (also bound to M-%<\/code>)), and regex find-and-replaces (M-x replace-regexp<\/code> and M-x query-replace-regexp<\/code> (also bound to C-M-%<\/code>)) are damn powerful. But sometimes, when a sed script won’t do, an elisp find-and-replace can save you a lot of pain.<\/p>\n

To do an elisp find-and-replace, do a regular replace-regexp<\/code>, and set the replacement expression to \\,<\/code> (backslash-comma) followed by an elisp expression. You can use backreferences \\1<\/code> through \\9<\/code> as string variables, and you can use \\#<\/code> as an integer variable that is the total number of replacements made so far.<\/p>\n

Steve has a number of great examples<\/a> which I’m not going to repeat here, so I encourage you to go over there and eat ’em up.<\/p>\n

I was eager to try them out, and seeing as how Emacs 22 is over two and half years old<\/a>, I figured my current Emacs install would be up-to-date. Not so – my MacBook was still running Emacs 21.2.1, which came installed when I bought it in 2006. Fortunately, with MacPorts<\/a> installed (HIGHLY<\/b> recommended for anyone running OS X), upgrading was almost<\/em> as easy as running<\/p>\n

sudo port install emacs<\/code><\/p>\n

I did install<\/code> instead of upgrade<\/code> because my emacs install was the default one that came installed and I hadn’t migrated it into MacPorts yet. I said it was almost<\/em> that easy because after it installed and I went to run it, the old Emacs 21 ran instead, even though the MacPorts binaries directory \/opt\/local\/bin<\/code> precedes \/usr\/bin<\/code> in my $PATH. It turns out that bash uses a hash table<\/a>, of which I was previously unaware, to cache where frequently used commands are located to avoid searching your $PATH frequently. To fix this, just run hash -d emacs<\/code> to delete its binding for emacs (or hash -r<\/code> to clear the entire table), and you’re good to go!<\/p>\n","protected":false},"excerpt":{"rendered":"

I was reading through some of the Coding Horror archives, and came across this post examining Microsoft Visual Studio’s use of regular expressions in its find-and-replace dialog. Visual Studio has support for all of the usual regex constructs but throws in a lot of its own quirky constructs too. I suppose they could be useful […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12],"tags":[],"class_list":["post-22","post","type-post","status-publish","format-standard","hentry","category-tools"],"_links":{"self":[{"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/posts\/22","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/comments?post=22"}],"version-history":[{"count":0,"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/posts\/22\/revisions"}],"wp:attachment":[{"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/media?parent=22"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/categories?post=22"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/adamrosenfield.com\/blog\/wp-json\/wp\/v2\/tags?post=22"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}