Add Have Script ShellCheck Itself When Executing as a Unix TIL

Author: jbranchaud

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).
 
-_1630 TILs and counting..._
+_1631 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Ruby Operator Lookup](https://www.visualmode.dev/ruby-operators)
@@ -1588,6 +1588,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Grep For Files Without A Match](unix/grep-for-files-without-a-match.md)
 - [Grep For Files With Multiple Matches](unix/grep-for-files-with-multiple-matches.md)
 - [Grep For Multiple Patterns](unix/grep-for-multiple-patterns.md)
+- [Have Script ShellCheck Itself When Executing](unix/have-script-shellcheck-itself-when-executing.md)
 - [Hexdump A Compiled File](unix/hexdump-a-compiled-file.md)
 - [Ignore A Directory During ripgrep Search](unix/ignore-a-directory-during-ripgrep-search.md)
 - [Ignore The Alias When Running A Command](unix/ignore-the-alias-when-running-a-command.md)

unix/have-script-shellcheck-itself-when-executing.md

@@ -0,0 +1,60 @@
+# Have Script ShellCheck Itself When Executing
+
+The [ShellCheck](https://www.shellcheck.net/) utility can be run against bash
+scripts to check if there are any warnings or errors we should fix. It works
+great as long as we remember to run it.
+
+I wondered if I could make it easier on myself by not having to remember to run
+it. What if my bash script were to `shellcheck` itself?
+
+Here is an example script where at the beginning it looks for and runs the
+`shellcheck` utility against `$0` (the path of the script). This is kind of
+meta. As the script is executing, it has an external program run against the
+entire contents of itself. If there are any `shellcheck` issues, they get
+displayed and the program exits early.
+
+```bash
+#!/bin/bash
+
+# Exit immediately if any command fails
+set -e
+
+# Self-validation using ShellCheck
+if command -v shellcheck &> /dev/null; then
+    echo "Validating script with ShellCheck..."
+
+    # $0 refers to the script itself
+    if ! shellcheck "$0"; then
+        echo "ShellCheck found issues in the script. Exiting."
+        exit 1
+    fi
+    echo "Script validation passed."
+else
+    echo "Warning: ShellCheck not found. Skipping validation."
+fi
+
+echo "Script execution continuing..."
+
+# shellcheck warning here
+read -p "Continue with current operation? (yes/no): " CONTINUE_WITH_EXISTING
+if [[ ! "$CONTINUE_WITH_EXISTING" =~ ^[Yy][Ee][Ss]$ ]]; then
+    echo "Operation cancelled."
+    exit 1
+fi
+```
+
+This last bit of the script with the `read` command will trigger a warning from
+`shellcheck`.
+
+```bash
+$ ./check.sh
+Validating script with ShellCheck...
+
+In ./check.sh line 23:
+read -p "Continue with current operation? (yes/no): " CONTINUE_WITH_EXISTING
+^--^ SC2162 (info): read without -r will mangle backslashes.
+
+For more information:
+  https://www.shellcheck.net/wiki/SC2162 -- read without -r will mangle backs...
+ShellCheck found issues in the script. Exiting.
+```