Add Check If A File Has Changed In A Script as a Git TIL

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).
 
-_1670 TILs and counting..._
+_1672 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -83,6 +83,7 @@ If you've learned something here, support my efforts writing daily TILs by
 * [SQLite](#sqlite)
 * [Streaming](#streaming)
 * [Tailwind CSS](#tailwind-css)
+* [Taskfile](#taskfile)
 * [tmux](#tmux)
 * [TypeScript](#typescript)
 * [Unix](#unix)
@@ -320,6 +321,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Caching Credentials](git/caching-credentials.md)
 - [Change The Start Point Of A Branch](git/change-the-start-point-of-a-branch.md)
 - [Check How A File Is Being Ignored](git/check-how-a-file-is-being-ignored.md)
+- [Check If A File Has Changed In A Script](git/check-if-a-file-has-changed-in-a-script.md)
 - [Checking Commit Ancestry](git/checking-commit-ancestry.md)
 - [Checkout Old Version Of A File](git/checkout-old-version-of-a-file.md)
 - [Checkout Previous Branch](git/checkout-previous-branch.md)
@@ -1494,6 +1496,10 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Specify Paths For Purging Unused CSS](tailwind/specify-paths-for-purging-unused-css.md)
 - [Use Tailwind Typography Prose In Dark Mode](tailwind/use-tailwind-typography-prose-in-dark-mode.md)
 
+### Taskfile
+
+- [Run A Task If It Meets Criteria](taskfile/run-a-task-if-it-meets-criteria.md)
+
 ### tmux
 
 - [Access Past Copy Buffer History](tmux/access-past-copy-buffer-history.md)

Taskfile.yml

@@ -51,7 +51,7 @@ tasks:
       - git commit -m "Update notes - $(date '+%Y-%m-%d %H:%M')"
       - git push
     status:
-      - git add NOTES.md && git diff --cached --quiet
+      - git diff --exit-code NOTES.md
     silent: false
 
   notes:status:

git/check-if-a-file-has-changed-in-a-script.md

@@ -0,0 +1,38 @@
+# Check If A File Has Changed In A Script
+
+If I'm at the command line and I want to check if a file has changed, I can run
+`git diff` and see what has changed. If I want to be more specific, I can run
+`git diff README.md` to see if there are changes to that specific file.
+
+If I'm trying to do this check in a script though, I want the command to clearly
+tell the script _Yes_ or _No_. Usually a script looks for an exit code to
+determine what path to take. But as long as `git diff` runs successfully,
+regardless of whether or not their are changes, it is going to have an
+affirmative exit code of `0`.
+
+This is why `git diff` offers the `--exit-code` flag.
+
+> Make the program exit with codes similar to diff(1). That is, it exits with 1
+> if there were differences and 0 means no differences.
+
+With that in mind, we can wire up a script with `git diff` that takes different
+paths depending on whether or not there are changes.
+
+```bash
+if ! git diff --exit-code README.md; then
+  echo "README.md has changes"
+else
+  echo "README.md is clean"
+fi
+```
+
+We can take this a step further and instead use the `--quiet` flag.
+
+> Disable all output of the program. Implies --exit-code. Disables execution of
+> external diff helpers whose exit code is not trusted
+
+This exhibits the same behavior as `--exit-code` and goes the additional step of
+silencing diff output and disabling execution of external diff helpers like
+`delta`.
+
+See `man git-diff` for more details.

taskfile/run-a-task-if-it-meets-criteria.md

@@ -0,0 +1,31 @@
+# Run A Task If It Meets Criteria
+
+The [Taskfile `status`
+directive](https://taskfile.dev/docs/guide#limiting-when-tasks-run) can be used
+to tell a task when it needs to run. If it doesn't need to run, it can be
+skipped over. The idea being that we're making a status check to see if we're
+up-to-date or need to run the task.
+
+For instance, here is a `status` check that determines if there are changes to
+commit and push. If there are changes to `NOTES.md`, then we are out-of-date and
+need to run the `cmds` that make up the task.
+
+```yaml
+  notes:push:
+    desc: Commit and push changes to notes submodule
+    dir: '{{.NOTES_DIR}}'
+    cmds:
+      - git add NOTES.md
+      - git commit -m "Update notes - $(date '+%Y-%m-%d %H:%M')"
+      - git push
+    status:
+      - git diff --exit-code NOTES.md
+    silent: false
+```
+
+This is useful because I don't want the `git add`, `git commit`, and `git push`
+commands to run when there is nothing to do.
+
+Note: this is different from the `preconditions` directive. Instead of
+short-circuiting a sequence of tasks, this will either run or skip the task and
+move on to the next one.