multifile grep: perform greps in series

Passing a very long argument list to git-grep can cause it to fail;
indeed, it's possible for the list of paths passed by git-secrets to
either grep or git-grep to exceed the maximum number of arguments
allowed in a user's environment (`getconf ARG_MAX`). Instead, let xargs
check that the number of arguments won't exceed the system limit.

Signed-off-by: Emily Shaffer <[email protected]>

Author: nasamuffin

git-secrets

@@ -111,18 +111,61 @@ scan_history() {
 git_grep() {
   local options="$1"; shift
   local files=("${@}") combined_patterns=$(load_combined_patterns)
+  local status=0
 
   [ -z "${combined_patterns}" ] && return 1
-  GREP_OPTIONS= LC_ALL=C git grep -nwHEI ${options} "${combined_patterns}" -- "${files[@]}"
+
+  if [ ${#files[@]} -eq 0 ]; then
+    GREP_OPTIONS= LC_ALL=C git grep -nwHEI ${options} "${combined_patterns}"
+    return $?
+  fi
+
+  # let xargs watch for system limit on arg count for us
+  printf "%s\n" "${files[@]}" |
+    GREP_OPTIONS= LC_ALL=C xargs -d'\n' sh -c \
+      'git grep "$@"; rc=$?; if [ $rc -eq 1 ]; then exit 0; else exit 1; fi' - \
+	-nwHEI "${options}" "${combined_patterns}" --
+  status=$?
+
+  # xargs returns 0 if all invocations returned 0, and we inverted the output
+  if [ $status -eq 0 ]; then
+    return 1
+  else
+    return 0
+  fi
 }
 
 # Performs a regular grep, taking into account patterns and recursion.
 # Note: this function returns 1 on success, 0 on error.
 regular_grep() {
   local files=("${@}") patterns=$(load_patterns) action='skip'
+  local status=0
   [ -z "${patterns}" ] && return 1
   [ ${RECURSIVE} -eq 1 ] && action="recurse"
-  GREP_OPTIONS= LC_ALL=C grep -d "${action}" -nwHEI "${patterns}" "${files[@]}"
+
+  if [ "${files[@]}" = "-" ]; then
+    GREP_OPTIONS= LC_ALL=C grep -d "${action}" -nwHEI "${patterns}" -
+    return $?
+  fi
+
+  # let xargs watch for system limit on arg count for us
+  printf "%s\n" "${files[@]}" |
+    GREP_OPTIONS= LC_ALL=C xargs -d'\n' sh -c \
+      'grep "$@"; rc=$?; if [ $rc -eq 2 ]; then exit 255; elif [ $rc -eq 1 ]; \
+       then exit 0; else exit 1; fi' - \
+      -d "${action}" -nwHEI "${patterns}"
+  status=$?
+
+  # xargs returns 0 if all invocations returned 0, and we inverted the output
+  if [ $status -eq 0 ]; then
+    return 1
+  # we fudged the output of grep to return 255 on error instead of 2; xargs
+  # reports a 255 as 124
+  elif [ $status -eq 124 ]; then
+    return 2
+  else
+    return 0
+  fi
 }
 
 # Process the given status ($1) and output variables ($2).