[root@localhost ~]# cat ~/.bash_profile
# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/bin

export PATH
lshell="login shell will see this message"
echo $lshell
[root@localhost ~]# bash --login
login shell will see this message
[root@localhost ~]# exit
logout
[root@localhost ~]# bash --noprofile
[root@localhost ~]#

shell.c文件部分内容：

struct {
  char *name;
  int *value;
  int type;
} long_args[] = {
  { "debug", &debugging, Int },
  { "norc", &no_rc, Int },
  { "noprofile", &no_profile, Int },
  { "rcfile", (int *)&bashrc_file, Charp},
  { "version", &do_version, Int},
  { "quiet", &quiet, Int},
  { "login", &make_login_shell, Int},
  { "nolineediting", &no_line_editing, Int},
  { "nobraceexpansion", &no_brace_expansion, Int},
  { (char *)NULL, (int *)0x0, 0 }
};

main (argc, argv, env)

  if (!locally_skip_execution)
    {
      if (login_shell)
    maybe_execute_file ("/etc/profile");

      if (login_shell && !no_profile)  //如果加了bash --noprofile选项则不执行下面的脚本
    {
      /* If we are doing the .bash_profile, then don't do the .bashrc. */
      no_rc++;

      if (act_like_sh)
        maybe_execute_file ("~/.profile");
      else
        {
          if (maybe_execute_file ("~/.bash_profile") == 0)
        if (maybe_execute_file ("~/.bash_login") == 0)
          maybe_execute_file ("~/.profile");
        }

      /* I turn on the restrictions afterwards because it is explictly
         stated in the POSIX spec that PATH cannot be set in a restricted
         shell, except in .profile. */
      if (*++(argv[0]) == 'r')
        {
          set_var_read_only ("PATH");
          restricted++;
        }
    }

  /* If user supplied the "-login" flag, then set and invert LOGIN_SHELL. */
  if (make_login_shell)
    login_shell = -++login_shell;

如果加了bash --login则make_login_shell为1，login_shell为1。

lshell="login shell can see this message "
echo $lshell
[root@localhost ~]# cat /etc/profile |grep lshell
lshell="login shell can see this message "
echo $lshell
[root@localhost ~]# exit
logout
[root@localhost ~]# bash --login
login shell can see this message
login shell will see this message    //这里说明login shell会执行/etc/profile和~/.bash_profile文件。（如果存在的话，具体看上面）
[root@localhost ~]# exit
logout
You have new mail in /var/spool/mail/root
[root@localhost ~]# bash
[root@localhost ~]#

[root@RCD ~]# bash --noprofile
[root@RCD ~]# exit
exit
You have new mail in /var/spool/mail/root
[root@RCD ~]# bash --noprofile --login
bash-4.1# pwd
/root
bash-4.1#

看来~/.bash_profile可以设置用户名和主机和所在的目录。