Update cheatsheets

git-grep

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# git-grep
+
+> Find strings inside files anywhere in a repository's history.
+> Accepts a lot of the same flags as regular `grep`.
+> More information: <https://git-scm.com/docs/git-grep>.
+
+- Search for a string in tracked files:
+
+`git grep {{search_string}}`
+
+- Search for a string in files matching a pattern in tracked files:
+
+`git grep {{search_string}} -- {{file_glob_pattern}}`
+
+- Search for a string in tracked files, including submodules:
+
+`git grep --recurse-submodules {{search_string}}`
+
+- Search for a string at a specific point in history:
+
+`git grep {{search_string}} {{HEAD~2}}`
+
+- Search for a string across all branches:
+
+`git grep {{search_string}} $(git rev-list --all)`