public String [] buildCommandLine (FilePath script ) {
        if (command . startsWith ( "#!" )) {
            // interpreter override
            int end = command . indexOf ( '\n' );
            if (end < 0 )   end =command . length ();
            List <String > args = new ArrayList <String >();
            args . addAll (Arrays . asList (Util . tokenize (command . substring ( 0 ,end ). trim ())));
            args . add (script . getRemote ());
            args . set ( 0 ,args . get ( 0 ). substring ( 2 ));    // trim off "#!"
            return args . toArray ( new String [args . size ()]);
        } else
            return new String [] { getDescriptor (). getShellOrDefault (script . getChannel ()), "-xe" , script . getRemote ()};
    }

#!/bin/bash +x
...
...

INVOCATION
       A login shell is one whose first character of argument zero is a -, or one started with the --login option.

       An interactive shell is one started without non-option arguments and without the -c option whose standard input
       and error are both connected to terminals (as determined by isatty (3 )), or one started with the -i option.  PS1
       is set and $- includes i if bash is interactive, allowing a shell script or a startup file to test this  state.

       The following paragraphs describe how bash executes its startup files.  If any of the files exist but cannot be
       read, bash reports an error.  Tildes are expanded in file names as described below under Tilde Expansion in the
       EXPANSION section.

       When  bash  is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it
       first reads and executes commands from the file /etc/profile, if that file exists.  After reading that file, it
       looks   for  ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from
       the first one that exists and is readable.  The --noprofile option may be used when the  shell  is  started  to
       inhibit this behavior.

       When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.

       When  an  interactive  shell  that  is  not  a  login  shell  is started, bash reads and executes commands from
       ~/.bashrc, if that file exists.  This may be inhibited by using the --norc option.  The  --rcfile  file  option
       will force bash to read and execute commands from file instead of ~/.bashrc.

       When  bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV
       in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to
       read and execute.  Bash behaves as if the following command were executed:
              if [ -n " $BA SH_ENV" ]; then . " $BA SH_ENV"; fi
       but the value of the PATH variable is not used to search for the file name.

if [ -f ~/.bashrc ]; then
  . ~/.bashrc
fi

if [ -f /etc/bashrc ]; then
  . /etc/bashrc
fi

OPTIONS
       In  addition  to  the  single-character shell options documented in the description of the set builtin command,
       bash interprets the following options when it is invoked:

       -c string If the -c option is present, then commands are read from string.  If there are  arguments  after  the
                 string, they are assigned to the positional parameters, starting with $0.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see INVOCATION below ).
       -r        If the -r option is present, the shell becomes restricted (see RESTRICTED SHELL below ).
       -s        If  the  -s  option  is present, or if no arguments remain after option processing, then commands are
                 read from the standard input.  This option allows the positional parameters to be set  when  invoking
                 an interactive shell.
       -D        A  list  of all double-quoted strings preceded by $ is printed on the standard output.  These are the
                 strings that are subject to language translation when the current locale is not  C  or  POSIX.   This
                 implies the -n option; no commands will be executed.

#!/bin/bash -ilex
...

...