Use plain sh for the pre-commit script

Bash is currently a dependency of pre-commit. It is only used in the
pre-commit script, and the only bash-specific feature that is used is a
single array.

Use the `args` array instead, which works on plain sh (e.g.: POSIX sh).
This change drops bash as a runtime dependency.

Tested with busybox sh(ash) and OpenBSD's sh(ksh).

pre_commit/commands/install_uninstall.py

@@ -94,17 +94,10 @@ def _install_hook_script(
         before, rest = contents.split(TEMPLATE_START)
         _, after = rest.split(TEMPLATE_END)
 
-        # on windows always use `/bin/sh` since `bash` might not be on PATH
-        # though we use bash-specific features `sh` on windows is actually
-        # bash in "POSIXLY_CORRECT" mode which still supports the features we
-        # use: subshells / arrays
-        if sys.platform == 'win32':  # pragma: win32 cover
-            hook_file.write('#!/bin/sh\n')
-
         hook_file.write(before + TEMPLATE_START)
         hook_file.write(f'INSTALL_PYTHON={shlex.quote(sys.executable)}\n')
         args_s = shlex.join(args)
-        hook_file.write(f'ARGS=({args_s})\n')
+        hook_file.write(f"ARGS='{args_s}'\n")
         hook_file.write(TEMPLATE_END + after)
     make_executable(hook_path)
 

pre_commit/resources/hook-tmpl

@@ -1,19 +1,20 @@
-#!/usr/bin/env bash
+#!/bin/sh
 # File generated by pre-commit: https://pre-commit.com
 # ID: 138fd403232d2ddd5efb44317e38bf03
 
 # start templated
 INSTALL_PYTHON=''
-ARGS=(hook-impl)
+ARGS="hook-impl"
 # end templated
 
 HERE="$(cd "$(dirname "$0")" && pwd)"
-ARGS+=(--hook-dir "$HERE" -- "$@")
+set -- $ARGS --hook-dir "$HERE" -- "$@"
 
 if [ -x "$INSTALL_PYTHON" ]; then
-    exec "$INSTALL_PYTHON" -mpre_commit "${ARGS[@]}"
+    exec "$INSTALL_PYTHON" -mpre_commit "$@"
+
 elif command -v pre-commit > /dev/null; then
-    exec pre-commit "${ARGS[@]}"
+    exec pre-commit "$@"
 else
     echo '`pre-commit` not found.  Did you forget to activate your virtualenv?' 1>&2
     exit 1