Enable extended regex in assert_file_contains

README.md

@@ -739,9 +739,11 @@ path : /path/to/non-empty-file
 Fail if the given file does not contain the regex.
 ```bash
 @test 'assert_file_contains() {
-    assert_file_contains /path/to/non-empty-file regex
+    assert_file_contains /path/to/non-empty-file regex engine
 }
 ```
+`engine` is optional and can be one of `grep`, `egrep` or `pcregrep`. The specified engine must be available on the system running the tests.
+
 On failure, the path and expected regex are displayed.
 
 [Back to index](#Index-of-all-functions)

src/file.bash

@@ -543,6 +543,7 @@ assert_file_size_equals() {
 # Arguments:
 #   $1 - path
 #   $2 - regex
+#   $3 - grep engine to use (grep, egrep, pcregrep) - optional
 # Returns:
 #   0 - file contains regex
 #   1 - otherwise
@@ -551,7 +552,21 @@ assert_file_size_equals() {
 assert_file_contains() {
   local -r file="$1"
   local -r regex="$2"
-  if ! grep -q "$regex" "$file"; then
+  local -r cmd="${3:-grep}"
+
+  case "$cmd" in
+    grep|egrep|pcregrep)
+      if ! type "${cmd}" &>/dev/null; then
+        batslib_decorate "Regex engine \"${cmd}\" not available on this system" \
+          | fail
+      fi
+    ;;
+    *)
+      batslib_decorate "Regex engine \"${cmd}\" not in allow list" \
+      | fail  
+    ;;
+  esac
+  if ! "$cmd" -q "$regex" "$file"; then
     local -r rem="${BATSLIB_FILE_PATH_REM-}"
     local -r add="${BATSLIB_FILE_PATH_ADD-}"
     batslib_print_kv_single 4 'path' "${file/$rem/$add}" \