grep: add executables attribute and determine_version method (#47438)

var/spack/repos/builtin/packages/grep/package.py

@@ -2,6 +2,8 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import re
+
 from spack.package import *
 
 
@@ -14,6 +16,8 @@ class Grep(AutotoolsPackage):
 
     license("GPL-3.0-or-later")
 
+    executables = ["^grep$"]
+
     version("3.11", sha256="1db2aedde89d0dea42b16d9528f894c8d15dae4e190b59aecc78f5a951276eab")
     version("3.10", sha256="24efa5b595fb5a7100879b51b8868a0bb87a71c183d02c4c602633b88af6855b")
     version("3.9", sha256="abcd11409ee23d4caf35feb422e53bbac867014cfeed313bb5f488aca170b599")
@@ -29,6 +33,14 @@ class Grep(AutotoolsPackage):
     depends_on("pcre2", when="@3.8:+pcre")
     depends_on("pcre", when="@:3.7+pcre")
 
+    @classmethod
+    def determine_version(cls, exe):
+        output = Executable(exe)("--version", output=str, error=str)
+        # Example output:
+        #     grep (GNU grep) 3.11
+        match = re.search(r"^grep \(GNU grep\) ([0-9.]+)", output)
+        return match.group(1) if match else None
+
     def configure_args(self):
         args = []