Improve error message when the shell can't execute a command.

Also, the exit code is now 126 when permission is denied, as specified
by POSIX.

Also: tiny tweaks to 'alias'.  Realized that we need to parse
incrementally.

core/builtin.py

@@ -999,7 +999,6 @@ def Alias(argv, aliases):

  for arg in argv:
    parts = arg.split('=', 1)
    log(' p %s', parts)
    if len(parts) == 1:
      name = parts[0]
      alias_exp = aliases.get(name)
@@ -1011,8 +1010,8 @@ def Alias(argv, aliases):
      name, alias_exp = parts
      aliases[name] = alias_exp

  print(argv)
  print(aliases)
  #print(argv)
  #log('AFTER ALIAS %s', aliases)
  return 0

core/process.py

@@ -323,14 +323,22 @@ def ExecExternalProgram(argv, environ):
  try:
    os.execvpe(argv[0], argv, environ)
  except OSError as e:
    log('Unexpected error in execvpe(%r, %r, ...): %s', argv[0], argv, e)
    util.error('%r: %s', argv[0], os.strerror(e.errno))
    # POSIX mentions 126 and 127 for two specific errors.  The rest are
    # unspecified.
    #
    # http://pubs.opengroup.org/onlinepubs/9699919799.2016edition/utilities/V3_chap02.html#tag_18_08_02

    # TODO:
    # - Make this error look better.
    # - What about permission errors?
    if e.errno == errno.EACCES:
      status = 126
    elif e.errno == errno.ENOENT:
      status = 127  # e.g. command not found should be 127.
    else:
      # dash uses 2, but we use that for parse errors.  This seems to be
      # consistent with mksh and zsh.
      status = 127

    # Command not found means 127.
    sys.exit(127)
    sys.exit(status)
  # no return

osh/cmd_parse.py

@@ -125,7 +125,10 @@ def __init__(self, w_parser, lexer, line_reader, arena, aliases=None):
    self.lexer = lexer  # for fast lookahead to (, for function defs
    self.line_reader = line_reader  # for here docs
    self.arena = arena  # for adding here doc spans
    self.aliases = aliases or {}  # aliases to expand at parse time
    if aliases is None:
      self.aliases = {}
    else:
      self.aliases = aliases  # aliases to expand at parse time

    self.Reset()

@@ -1201,6 +1204,7 @@ def ParseCommand(self):
    ok, word_str, quoted = word.StaticEval(self.cur_word)
    if ok and not quoted:
      alias_exp = self.aliases.get(word_str)
      #log('AT PARSE TIME %s', self.aliases)
      if alias_exp is not None:
        log('expand %s -> %s', word_str, alias_exp)

spec/command_.test.sh

@@ -6,3 +6,17 @@
{ which ls; }
## stdout: /bin/ls

#### Permission denied
touch $TMP/text-file
$TMP/text-file
## status: 126

#### Not a dir
$TMP/not-a-dir/text-file
## status: 127

#### Name too long
./0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789
## status: 127
## OK dash status: 2
## OK bash status: 126

test/spec.sh

@@ -371,8 +371,7 @@ command-sub() {
}

command_() {
  sh-spec spec/command_.test.sh \
    ${REF_SHELLS[@]} $OSH_LIST "$@"
  sh-spec spec/command_.test.sh ${REF_SHELLS[@]} $ZSH $OSH_LIST "$@"
}

pipeline() {