bash.hlp

bash帮助手册

BASH(1)								       BASH(1)



NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [file]

COPYRIGHT
       Bash is Copyright (C) 1989-2002 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 incor-
       porates useful features from the Korn and C shells (ksh and csh).

       Bash  is	 intended  to be a conformant implementation of the IEEE POSIX
       Shell and Tools specification (IEEE Working Group 1003.2).

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 ouput.	 These are the strings that  are  sub-
		 ject 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 invocation  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 file-
		 names 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.

       --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 success-
	      fully.
       --init-file file
       --rcfile file
	      Execute commands from file instead of the standard personal ini-
	      tialization  file	 ~/.bashrc  if	the  shell is interactive (see
	      INVOCATION below).

       --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).

       --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.

       --posix
	      Change  the behavior of bash where the default operation differs
	      from the POSIX 1003.2 standard  to  match	 the  standard	(posix
	      mode).

       --restricted
	      The shell becomes restricted (see RESTRICTED SHELL below).

       --rpm-requires
	      Produce the list of files that are required for the shell script
	      to run.  This implies '-n' and is subject to  the	 same  limita-
	      tions  as	 compile  time	error checking checking; Backticks, []
	      tests,  and evals are not parsed so  some	 dependencies  may  be
	      missed.  --verbose Equivalent to	-v.

       --version
	      Show  version information for this instance of bash on the stan-
	      dard 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 parame-
       ters are set to the remaining arguments.	 Bash reads and executes  com-
       mands  from this file, then exits.  Bash's exit status is the exit sta-
       tus 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.

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 output are both con-
       nected 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 Expan-
       sion in the EXPANSION section.

       When  bash is invoked as an interactive login shell, or as a non-inter-
       active shell with the --login option, it first reads and executes  com-
       mands  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 com-
       mand 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.

       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 interac-
       tive 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 exe-
       cute  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.

DEFINITIONS
       The following definitions are used throughout the rest  of  this	 docu-
       ment.
       blank  A space or tab.
       word   A	 sequence  of  characters  considered  as a single unit by the
	      shell.  Also known as a token.
       name   A word consisting only of	 alphanumeric  characters  and	under-
	      scores,  and beginning with an alphabetic character or an under-
	      score.  Also referred to as an identifier.
       metacharacter
	      A character that, when unquoted, separates words.	  One  of  the
	      following:
	      |	 & ; ( ) < > space tab
       control operator
	      A token that performs a control function.	 It is one of the fol-
	      lowing symbols:
	      || & && ; ;; ( ) | <newline>

RESERVED WORDS
       Reserved words are words that have a special meaning to the shell.  The
       following words are recognized as reserved when unquoted and either the
       first word of a simple command (see SHELL GRAMMAR below) or  the	 third
       word of a case or for command:

       !  case	do done elif else esac fi for function if in select then until
       while { } time [[ ]]

SHELL GRAMMAR
   Simple Commands
       A simple command is a sequence of optional  variable  assignments  fol-
       lowed  by  blank-separated  words and redirections, and terminated by a
       control operator.  The first word specifies the command to be executed,
       and  is	passed	as  argument  zero.  The remaining words are passed as
       arguments to the invoked command.

       The return value of a simple command is its exit status,	 or  128+n  if
       the command is terminated by signal n.

   Pipelines
       A pipeline is a sequence of one or more commands separated by the char-
       acter |.	 The format for a pipeline is:

	      [time [-p]] [ ! ] command [ | command2 ... ]

       The standard output of command is connected via a pipe to the  standard
       input  of  command2.   This connection is performed before any redirec-