From c2e4a2962961b760f0fe47fa3228eafceff8e2b8 Mon Sep 17 00:00:00 2001
From: jbranchaud <jbranchaud@gmail.com>
Date: Fri, 28 Apr 2023 09:04:29 -0500
Subject: [PATCH] Add Negative Look-Ahead Search With ripgrep as a Unix TIL

---
 README.md                                     |  3 +-
 ...negative-look-ahead-search-with-ripgrep.md | 40 +++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 unix/negative-look-ahead-search-with-ripgrep.md

diff --git a/README.md b/README.md
index 26aac02..6037ac8 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1296 TILs and counting..._
+_1297 TILs and counting..._
 
 ---
 
@@ -1282,6 +1282,7 @@ _1296 TILs and counting..._
 - [List The Available JDKs](unix/list-the-available-jdks.md)
 - [List The Stack Of Remembered Directories](unix/list-the-stack-of-remembered-directories.md)
 - [Map A Domain To localhost](unix/map-a-domain-to-localhost.md)
+- [Negative Look-Ahead Search With ripgrep](unix/negative-look-ahead-search-with-ripgrep.md)
 - [Occupy A Local Port With Netcat](unix/occupy-a-local-port-with-netcat.md)
 - [Only Show The Matches](unix/only-show-the-matches.md)
 - [Open The Current Command In An Editor](unix/open-the-current-command-in-an-editor.md)
diff --git a/unix/negative-look-ahead-search-with-ripgrep.md b/unix/negative-look-ahead-search-with-ripgrep.md
new file mode 100644
index 0000000..2fc4f96
--- /dev/null
+++ b/unix/negative-look-ahead-search-with-ripgrep.md
@@ -0,0 +1,40 @@
+# Negative Look-Ahead Search With ripgrep
+
+I have a huge monorepo with a bunch of instances of the
+`NEXT_PUBLIC_SANITY_DATASET` env var that need to be updated to
+`NEXT_PUBLIC_SANITY_DATASET_ID` (notice the `_ID` appended to the end). If I do
+a basic search for `NEXT_PUBLIC_SANITY_DATASET`, I get a huge list of results
+cluttered with all the instances where this env var has already been updated.
+
+To get a list of _only_ the places where the old env var, and not the new env
+var, appear, I need to use [a regex feature called a negative
+look-ahead](https://www.regular-expressions.info/lookaround.html). That looks
+something like `PATTERN(?!NLA)` where we want to match on `PATTERN`, but not if
+it is immediately followed by `NLA`.
+
+Let's try that with [ripgrep](https://github.com/BurntSushi/ripgrep):
+
+```bash
+$ rg 'NEXT_PUBLIC_SANITY_DATASET(?!_ID)' --hidden --glob '!node_modules/**' --glob '!.git/**'
+regex parse error:
+    NEXT_PUBLIC_SANITY_DATASET(?!_ID)
+                              ^^^
+error: look-around, including look-ahead and look-behind, is not supported
+
+Consider enabling PCRE2 with the --pcre2 flag, which can handle backreferences
+and look-around.
+```
+
+It doesn't work as is, but the error message helpfully tells me that I need to
+include the `--pcre2` flag for look-ahead to work.
+
+Let's try that again:
+
+```bash
+❯ rg --pcre2 'NEXT_PUBLIC_SANITY_DATASET(?!_ID)' --hidden --glob '!node_modules/**' --glob '!.git/**'
+apps/testing-javascript/.env.development
+37:NEXT_PUBLIC_SANITY_DATASET=production
+...
+```
+
+That works!