Add a 'repr' builtin for debugging.

It's a lot easier to type than:

argv.py "${a[@]}"

core/builtin.py

@@ -116,6 +116,9 @@
     "unalias": builtin_e.UNALIAS,
 
     "help": builtin_e.HELP,
+
+    # OSH only
+    "repr": builtin_e.REPR,
 }
 
 
@@ -1340,6 +1343,23 @@ def Help(argv, loader):
   return 0
 
 
+def Repr(argv, mem):
+  """Given a list of variable names, print their values.
+
+  'repr a' is a lot easier to type than 'argv.py "${a[@]}"'.
+  """
+  status = 0
+  for name in argv:
+    # TODO: Should we print flags too?
+    val = mem.GetVar(name)
+    if val.tag == value_e.Undef:
+      print('%r is not defined' % name, file=sys.stderr)
+      status = 1
+    else:
+      print('%s = %s' % (name, val))
+  return status
+
+
 def main(argv):
   # Localization: Optionally  use GNU gettext()?  For help only.  Might be
   # useful in parser error messages too.  Good thing both kinds of code are

core/cmd_exec.py

@@ -362,6 +362,9 @@ def _RunBuiltin(self, builtin_id, argv, span_id):
       loader = util.GetResourceLoader()
       status = builtin.Help(argv, loader)
 
+    elif builtin_id == builtin_e.REPR:
+      status = builtin.Repr(argv, self.mem)
+
     else:
       raise AssertionError('Unhandled builtin: %s' % builtin_id)
 

core/runtime.asdl

@@ -75,6 +75,7 @@ module runtime
   | COMMAND | TYPE | HELP
   | DECLARE | TYPESET | ALIAS | UNALIAS
   | PWD
+  | REPR
 
   -- word_eval.py: SliceParts is for ${a-} and ${a+}, Error is for ${a?}, and
   -- SliceAndAssign is for ${a=}.

spec/osh-only.test.sh

@@ -13,6 +13,19 @@ set -o debug-completion
 $SH -o debug-completion
 ## status: 0
 
+#### repr
+x=42
+repr x
+echo status=$?
+repr nonexistent
+echo status=$?
+## STDOUT:
+x = (Str s:42)
+status=0
+status=1
+## END
+
+
 #### crash dump
 rm -f $TMP/*.json
 OSH_CRASH_DUMP_DIR=$TMP $SH -c '