bash帮助文档简单学习；bash手册翻译
关于bash的四种工作方式的不同，可以参考：http://feihu.me/blog/2014/env-problem-when-ssh-executing-command-on-remote/，但是由于每个linux系统都有不同表现，只可以参考，实际还要以你当前的linux系统为准
bash的文档还是要学习的：man -a bash
BASH(1) BASH(1) NAME bash - GNU Bourne-Again SHell SYNOPSIS bash [options] [file] COPYRIGHT Bash is Copyright (C) 1989-2005 by the Free Software Foundation, Inc. DESCRIPTION Bash is an sh-compatible command language interpreter that executes commands read from the standard input or from a file. Bash also incorporates useful features from the Korn and C shells (ksh and csh).
译：Bash是个兼容sh的命令行语音解释器，可以执行来自标准输入或来自文件的命令。Bash吸收了Korn和C shells的很多特征 Bash is intended to be a conformant implementation of the Shell and Utilities portion of the IEEE POSIX specification (IEEE Standard 1003.1). Bash can be configured to be POSIX-conformant by default.
译：Bash试图把自己打造成符合POSIX（Portable Operating System Interface of UNIX）接口规范的一个工具和Shell应用。而且Bash默认情况下是可以配置成符合POSIX规范的 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:
译：除了在内置命令set的文档(man -a set)里描述的shell选项，bash还可支持以下选项 -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.
译：-c选项的作用是，读取后面字符串的内容做为命令来执行。如果字符串后面还有参数，这些参数可以通过$0/$1...的方式被字符串里的命令引用(举例：执行bash -c 'echo $1 $0' shen 申 ；输出：申 shen) -i If the -i option is present, the shell is interactive.
译：-i的作用是，是shell变为交互式shell -l Make bash act as if it had been invoked as a login shell (see INVOCATION below).
译：-l的作用是使bash变成一个login shell -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.
译： -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. [-+]O [shopt_option] shopt_option is one of the shell options accepted by the shopt builtin (see SHELL BUILTIN COMMANDS below). If shopt_option is present, -O sets the value of that option; +O unsets it. If shopt_option is not supplied, the names and values of the shell options accepted by shopt are printed on the standard output. If the invo- cation option is +O, the output is displayed in a format that may be reused as input. -- A -- signals the end of options and disables further option processing. Any arguments after the -- are treated as filenames and arguments. An argument of - is equivalent to --. Bash also interprets a number of multi-character options. These options must appear on the command line before the single-character options to be recognized. 译：bash也支持大量的多字符选项，但是前提是这些多字符选择要出现在单字符选项前面 --debugger Arrange for the debugger profile to be executed before the shell starts. Turns on extended debugging mode (see the description of the extdebug option to the shopt builtin below) and shell function tracing (see the description of the -o functrace option to the set builtin below). --dump-po-strings Equivalent to -D, but the output is in the GNU gettext po (portable object) file format. --dump-strings Equivalent to -D. --help Display a usage message on standard output and exit successfully.
--init-file file
--rcfile file
Execute commands from file instead of the standard personal initialization file ~/.bashrc if the shell is interactive (see INVOCATION below).
译：在交互式shell中，会读取~/.bashrc文件，如果有这个选项，则读取--rcfile后面的file
--login
Equivalent to -l.
--noediting
Do not use the GNU readline library to read command lines when the shell is interactive.
--noprofile
Do not read either the system-wide startup file /etc/profile or any of the personal initialization files ~/.bash_profile, ~/.bash_login, or ~/.profile. By default, bash
reads these files when it is invoked as a login shell (see INVOCATION below).
译：在login shell中，会默认读取/etc/profile，~/.bash_profile, ~/.bash_login, or ~/.profile.的内容，首先读取/etc/profile,然后只读取后面三个中的其中一个，按顺序读取找到的第一个文件。如果有此--noprofile选项，则不会读取这些文件
--norc Do not read and execute the personal initialization file ~/.bashrc if the shell is interactive. This option is on by default if the shell is invoked as sh.
译：在交互式的shell中，不要读取个人的初始化文件~/.bashrc。在使用sh时，这是默认选项。也就是说，使用sh的时候，默认是不会读取~/.bashrc文件的
--posix
Change the behavior of bash where the default operation differs from the POSIX standard to match the standard (posix mode).
--restricted
The shell becomes restricted (see RESTRICTED SHELL below).
--verbose
Equivalent to -v.
--version
Show version information for this instance of bash on the standard output and exit successfully.
ARGUMENTS
If arguments remain after option processing, and neither the -c nor the -s option has been supplied, the first argument is assumed to be the name of a file containing shell
commands. If bash is invoked in this fashion, $0 is set to the name of the file, and the positional parameters are set to the remaining arguments. Bash reads and executes
commands from this file, then exits. Bash's exit status is the exit status of the last command executed in the script. If no commands are executed, the exit status is 0. An
attempt is first made to open the file in the current directory, and, if no file is found, then the shell searches the directories in PATH for the script.
译：如果没有使用选项-c和-s,并且其他选项后面还有参数，那么第一个参数表示文件名字。即$0是文件名，$1表示第一个参数。bash执行完这个bash文件后，退出。bash的退出状态取决于脚本里的最后一条命令。如果脚本里没有任何一条
命令，退出状态为0，bash首先在当前目录找后面的脚本文件，找不到，就去PATH路径下找
INVOCATION：主要讲解了不同shell状态，如何读取环境变量
A login shell is one whose first character of argument zero is a -, or one started with the --login option.
译：login shell的判别方法是：使用--login选项或者$0值的第一个字符是‘-’
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 $- includes i if bash is interactive, allowing a shell script or a startup file to test this state.
译：交互式shell的判别方法是：使用选项-i；没有使用选项-c(标准输入和错误都传到了终端)；不含no-option的参数
The following paragraphs describe how bash executes its startup files. If any of the files exist but cannot be read, bash reports an error. Tildes are expanded in file names
as described below under Tilde Expansion in the EXPANSION section.
译：下面段落的内容描述了bash是如何执行启动文件的。如果要读取的文件存在不可读，就会报错。文件名字中的波浪号的含义在下面的章节有解释
When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if
that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that
exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.
译：在交互式的login shell或者使用--login选项的非交互的shell情形，bash首先读取存在的/etc/profile。然后在按序读取三个文件~/.bash_profile, ~/.bash_login, and ~/.profile中的第一个出现的可读文件
When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.
译：login shell退出时，如果存在文件~/.bash_logout存在，bash就会读取。但是选项--noprofile会禁止读取这些文件
When an interactive shell that is not a login shell is started, bash reads and executes commands from ~/.bashrc, if that file exists. This may be inhibited by using the --norc
option. The --rcfile file option will force bash to read and execute commands from file instead of ~/.bashrc.
译：在交互式shell非login shell中，bash会读取可读且存在的~/.bashrc。选项--norc禁止读取~/.bashrc。选项--rcfile存在的时候，则读取后面的文件
When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and
uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
but the value of the PATH variable is not used to search for the file name.
译：在非交互式shell中，bash会去寻找BASH_ENV变量，把找到的变量值作为文件名进行读取。寻找文件的时候，不会去PATH路径下寻找
If bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of sh as closely as possible, while conforming to the POSIX standard as well.
When invoked as an interactive login shell, or a non-interactive shell with the --login option, it first attempts to read and execute commands from /etc/profile and ~/.profile,
in that order. The --noprofile option may be used to inhibit this behavior. When invoked as an interactive shell with the name sh, bash looks for the variable ENV, expands
its value if it is defined, and uses the expanded value as the name of a file to read and execute. Since a shell invoked as sh does not attempt to read and execute commands
from any other startup files, the --rcfile option has no effect. A non-interactive shell invoked with the name sh does not attempt to read any other startup files. When
invoked as sh, bash enters posix mode after the startup files are read.
When bash is started in posix mode, as with the --posix command line option, it follows the POSIX standard for startup files. In this mode, interactive shells expand the ENV
variable and commands are read and executed from the file whose name is the expanded value. No other startup files are read.
Bash attempts to determine when it is being run by the remote shell daemon, usually rshd. If bash determines it is being run by rshd, it reads and executes commands from
~/.bashrc, if that file exists and is readable. It will not do this if invoked as sh. The --norc option may be used to inhibit this behavior, and the --rcfile option may be
used to force another file to be read, but rshd does not generally invoke the shell with those options or allow them to be specified.
If the shell is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supplied, no startup files are read, shell functions
are not inherited from the environment, the SHELLOPTS variable, if it appears in the environment, is ignored, and the effective user id is set to the real user id. If the -p
option is supplied at invocation, the startup behavior is the same, but the effective user id is not reset.
交互式shell
login shell
参考：
1、https://www.2cto.com/shouce/linuxman/bash.1.html
