--- title: codemod + sed slug: codemod-sed published_at: 2020-03-20 17:46:19 +0000 updated_at: 2026-03-04 20:14:57 +0000 summary: description: How to make wide sweeping changes to a codebase with codemod or sed. https://github.com/facebook/codemod https://www.gnu.org/software/sed/manual/html_node/Addresses-overview.html tags: [sed, codemod, refactoring] views: 100 author: CJ Avilla url: https://www.cjav.dev/videos/codemod-sed youtube_url: https://www.youtube.com/watch?v=_ogopzhnOo8 youtube_id: _ogopzhnOo8 embed_url: https://www.youtube.com/embed/_ogopzhnOo8 thumbnail_url: https://i.ytimg.com/vi/_ogopzhnOo8/hqdefault.jpg type: video --- # codemod + sed *Published: March 20, 2020* *Views: 100* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=_ogopzhnOo8) [![codemod + sed](https://i.ytimg.com/vi/_ogopzhnOo8/hqdefault.jpg)](https://www.youtube.com/watch?v=_ogopzhnOo8) ## Description How to make wide sweeping changes to a codebase with codemod or sed. https://github.com/facebook/codemod https://www.gnu.org/software/sed/manual/html_node/Addresses-overview.html ## Transcript so I recently was working on a I'm working on a project to auto-generate striped net and something I wanted to do as part of that Auto generation was go through and remove all of the comments that were in the entities and in some of the service files and the there's a term it's like often thrown around an industry call where people say they've code modded or like made a codemod to the codebase and this is generally just like wide sweeping reef actors where they're making major changes across the codebase and so I had never done one of these before I'd used said a couple of times but I wasn't really sure what people were talking about when they said they were doing code mods and so the first thing that I thought you know you know the naively what you might do is just like open up the file that you're going to edit so in this case if we pull up one of the files that I want to remove comments for mmm here you'll see that like for instance this is one of the comments I wanted to remove the reason I'm doing this is because when I auto generate it's really hard to generate the comments so I want to just kind of like remove all the comments Auto generate the code look at the diff and see where the auto generation is failing compared to what's on master and that's a little easier if I don't have any comments so you might think okay I can just go in and like quickly remove all the comments but there's hundreds of files and so that wasn't gonna be something that you could do pretty easily even with vim like I could write some sort of macro or something to quickly go through and make that modification per file but I I really want to like get comfortable with tools to make these wide sweeping changes across the codebase so I found this tool called code mod by Facebook which is a Python package let's see it's a it's a Python package that you can pip install and then you can execute it like this you call code mod - D give it a directory and the extensions of the files that you want to change and then like a starting regular expression and ending regular expression so I I went and tried to use this they say code - M - D maybe source strife net entities and then the first argument that you pass is the code that you're going from so everything that's like starts with triple slash dot star and then replace it with just an empty string so I try to use this code mod thing and that's basically just copying the command that they have in the readme but this ends up deleting everything because the match is multi-line and so I'm not like checking to the end of the line I'm just checking like everything but this is kind of cool it walks you through an interactive prompt to see if you want to accept the change or not kind of like when you're doing a git patch that's interactive so that didn't work exactly it turns out that this - M is to apply this regular expression multi-line so if I remove that then I just get the one-line change so that looks great I'm just saying like okay just remove slash slash slash with summary yes I want to accept that yes I want to accept that yes okay so this looks like it's going well it's removing the right stuff so you can say a to accept all changes so there's a capital a and hit enter and just quickly runs through and applies all of those changes removing removing all of those lines so then if I look at the diff here I can see that the comments were removed but there's still white space like newline white space or not even not even newline just like white space at the beginning because I didn't as my regular expression didn't match like from the beginning of the line all the white space but even if I even if I modify my even if I modify my regular expression to match that in the beginning where I say like from the start of the line any white space up to the let's see let's stash that and then run this thing again and then apply all changes it will match from the beginning of the line but because I'm still replacing with empty string it doesn't actually replace those new lines so I'm still adding new they don't have the white space at the beginning but it's not deleting the line so I decided this probably wasn't gonna work and I wanted to use something else instead and so that seems like a really good tool and it would apply really well as long as you don't want to delete lines or maybe there's another way to do it I just I couldn't figure it out quickly and so the the tool that I reached for next was said which is a stream editor that you can use to inline edit files so the first step was to like just kind of mess around was said to figure out what I wanted it to do so you can use said - II - do you you can't you can pass - II a couple different times and - II is the the actual edit that you want to make and if you use - I that makes it an inline change and you can pass an extension for like the temporary files that it will make if you pass empty string it won't make temporary files that's totally cool so we say like - I empty empty string and then - II with the change we want to make so in this case we want to do something like find all of the find all of the comments and then do /d - delete delete the line and then we pass in the file so I just wanted to test it out on one file so we can say like striped net and then entities accounts account see s let's see if it if that worked okay so the regular expression was unterminated maybe this is supposed to be this way okay so then if we check yeah so this correctly deleted all of the comments so that's looking good so the next thing that I want to do is I want to try applying this to all the files that are in the entities and services directory so what I what I started out with was using fine dot and then like maybe looking for the expression that was in the files and then that didn't that didn't work super great and there was something about the way that the of files was being printed out that I couldn't pipe it into said for some reason so instead I ended up using a grep yeah so grep - RL with this slash slash slash to find all of the files that have these three lines in striped net in either my entities or services directories with the star so this you can use these Curly's to expand the blob out to include the source directory strike net directory and then both children entities and services and then I'm piping that into said with X args so X args is a way to take the list of files that's printed out from grep here and passing those as a the final argument to said so now I'm saying X args said - I empty empty string so it doesn't create temporary files and then - II this is the command to make the change and so when I run that now it has successfully modified all of these files here to remove the comments from all files so as part of autogen we'll probably go back and add all of the comments later once we have which we can get from the spec that I'm using to generate but initially when I'm trying to figure out just like the the fundamentals for how do you render certain properties on certain classes it's much easier to just work without the comments so remove the comments build an integration branch and then sort of like Auto generate and compare with the integration branch that doesn't have the comments so this was kind of helpful and I wanted to share just in case anyone else is curious about how to do like wide sweep being code mods or you know changes was said so using using said with using grep was said here was the was the tool that I think is pretty powerful and I hope it's hope it's useful alright see ya --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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