my-first-regex.md (2106B)
1 +++ 2 title = "My First RegEx" 3 date = 2021-01-21 4 +++ 5 6 `(?<=\.\/IssuerIcons\/).*(?=\.png)` 7 <!-- more --> 8 9 ## What it does 10 11 Let's break it apart piece by piece. It's meant to return the filename 12 from a given path in a specific format. When given 13 `./IssuerIcons/Example.png`, the script should return `Example`. 14 15 The first section is a positive lookbehind: `(?<=\.\/IssuerIcons\/)`. 16 This asserts that the selected portion must by preceeded by 17 `./IssuerIcons/`. 18 19 The section section is a pattern match: `.*`. This matches all 20 characters, excluding newlines, of any length. 21 22 The third and final section is a positive lookforward: `(?=\.png)`. 23 This asserts that the selected portion must be followed by `.png`. 24 25 ## Background 26 27 Yesterday, I wrote my first regular expression. I've always regarded 28 regex as an arcane art of true shell wizards – and for the most part, 29 I still do. Now though, I've gotten a glimpse of their world. 30 31 I wrote this expression for [Tofu][tofu], an open-source 2FA app for 32 iOS. I had been thinking of making more "issuer icons" for the app 33 when I noticed that the icons were all designed in one Sketch file. 34 This could become a problem if two people were to edit the file at 35 one time, so I suggested a [solution][issue]. 36 37 The author got back to me with another idea: ditch Sketch altogether, 38 and replace it with a shell script that generates icons from a 39 directory of `png`s. I [wrote it][pr]. I've since refined it, with 40 help from [ThinkChaos][tc], to make it independent of any preceding 41 directories using `sed`: `sed -E 's:.+/(.+)\.png:\1:'`. 42 43 It was a really fun experience – I've never written bash before! It 44 reminded me a lot of Drew DeVault's post [Become shell literate][sl]. 45 I work primarily from my terminal, and am slowly working my way up to 46 true mastery – I'm nowhere near close, but this was a step in the right 47 direction. 48 49 [tofu]: https://www.tofuauth.com/ 50 [issue]: https://github.com/calleerlandsson/Tofu/issues/52 51 [pr]: https://github.com/calleerlandsson/Tofu/pull/60 52 [sl]: https://drewdevault.com/2020/12/12/Shell-literacy.html 53 [tc]: https://github.com/ThinkChaos