bash.hlp

bash帮助手册

	      If this parameter is set when bash is executing a shell  script,
	      its  value  is  interpreted as a filename containing commands to
	      initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
	      subjected	 to  parameter	expansion,  command  substitution, and
	      arithmetic expansion before being interpreted as	a  file	 name.
	      PATH is not used to search for the resultant file name.
       CDPATH The  search  path for the cd command.  This is a colon-separated
	      list of directories in which the	shell  looks  for  destination
	      directories  specified  by  the  cd  command.  A sample value is
	      ".:~:/usr".
       COLUMNS
	      Used by the select builtin command  to  determine	 the  terminal
	      width  when  printing  selection	lists.	Automatically set upon
	      receipt of a SIGWINCH.
       COMPREPLY
	      An array variable from which bash reads the possible completions
	      generated	 by  a	shell  function	 invoked  by  the programmable
	      completion facility (see Programmable Completion below).
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
	      A colon-separated list of suffixes  to  ignore  when  performing
	      filename completion (see READLINE below).	 A filename whose suf-
	      fix matches one of the entries in FIGNORE is excluded  from  the
	      list of matched filenames.  A sample value is ".o:~".
       GLOBIGNORE
	      A colon-separated list of patterns defining the set of filenames
	      to be ignored by pathname expansion.  If a filename matched by a
	      pathname	expansion  pattern also matches one of the patterns in
	      GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
	      If set to a value of ignorespace, lines which begin with a space
	      character	 are  not  entered  on	the history list.  If set to a
	      value of ignoredups, lines matching the last  history  line  are
	      not  entered.   A	 value of ignoreboth combines the two options.
	      If unset, or if set to any other value  than  those  above,  all
	      lines  read by the parser are saved on the history list, subject
	      to the value of HISTIGNORE.  This variable's function is	super-
	      seded  by	 HISTIGNORE.   The  second  and	 subsequent lines of a
	      multi-line compound command are not tested, and are added to the
	      history regardless of the value of HISTCONTROL.
       HISTFILE
	      The name of the file in which command history is saved (see HIS-
	      TORY below).  The default value is ~/.bash_history.   If	unset,
	      the  command  history  is	 not  saved  when an interactive shell
	      exits.
       HISTFILESIZE
	      The maximum number of lines contained in the history file.  When
	      this  variable  is  assigned  a value, the history file is trun-
	      cated, if necessary, to contain no  more	than  that  number  of
	      lines.   The  default  value  is	500.  The history file is also
	      truncated to this size after  writing  it	 when  an  interactive
	      shell exits.
       HISTIGNORE
	      A	 colon-separated list of patterns used to decide which command
	      lines should be saved on the  history  list.   Each  pattern  is
	      anchored	at  the	 beginning of the line and must match the com-
	      plete line (no implicit  `*'  is	appended).   Each  pattern  is
	      tested  against  the line after the checks specified by HISTCON-
	      TROL are applied.	 In  addition  to  the	normal	shell  pattern
	      matching characters, `&' matches the previous history line.  `&'
	      may be escaped using  a  backslash;  the	backslash  is  removed
	      before attempting a match.  The second and subsequent lines of a
	      multi-line compound command are not tested, and are added to the
	      history regardless of the value of HISTIGNORE.
       HISTSIZE
	      The  number  of commands to remember in the command history (see
	      HISTORY below).  The default value is 500.
       HOME   The home directory of the current user; the default argument for
	      the cd builtin command.  The value of this variable is also used
	      when performing tilde expansion.
       HOSTFILE
	      Contains the name of a file in the  same	format	as  /etc/hosts
	      that should be read when the shell needs to complete a hostname.
	      The list of possible hostname completions may be	changed	 while
	      the  shell  is  running;	the  next  time hostname completion is
	      attempted after the value is changed, bash adds the contents  of
	      the  new file to the existing list.  If HOSTFILE is set, but has
	      no value, bash attempts to read /etc/hosts to obtain the list of
	      possible	hostname  completions.	 When  HOSTFILE	 is unset, the
	      hostname list is cleared.
       IFS    The Internal Field Separator that is  used  for  word  splitting
	      after  expansion	and  to	 split	lines into words with the read
	      builtin  command.	  The  default	value  is  ``<space><tab><new-
	      line>''.
       IGNOREEOF
	      Controls the action of an interactive shell on receipt of an EOF
	      character as the sole input.  If set, the value is the number of
	      consecutive  EOF	characters  which  must	 be typed as the first
	      characters on an input line before bash exits.  If the  variable
	      exists  but  does not have a numeric value, or has no value, the
	      default value is 10.  If it does not exist,  EOF	signifies  the
	      end of input to the shell.
       INPUTRC
	      The  filename  for  the  readline	 startup  file, overriding the
	      default of ~/.inputrc (see READLINE below).
       LANG   Used to determine the  locale  category  for  any	 category  not
	      specifically selected with a variable starting with LC_.
       LC_ALL This  variable  overrides	 the  value  of LANG and any other LC_
	      variable specifying a locale category.
       LC_COLLATE
	      This variable determines the collation order used	 when  sorting
	      the  results  of pathname expansion, and determines the behavior
	      of  range	 expressions,  equivalence  classes,   and   collating
	      sequences within pathname expansion and pattern matching.
       LC_CTYPE
	      This  variable  determines  the interpretation of characters and
	      the behavior of character classes within pathname expansion  and
	      pattern matching.
       LC_MESSAGES
	      This  variable  determines  the locale used to translate double-
	      quoted strings preceded by a $.
       LC_NUMERIC
	      This variable determines the locale  category  used  for	number
	      formatting.
       LINES  Used  by	the  select  builtin  command  to determine the column
	      length for printing selection  lists.   Automatically  set  upon
	      receipt of a SIGWINCH.
       MAIL   If  this	parameter is set to a file name and the MAILPATH vari-
	      able is not set, bash informs the user of the arrival of mail in
	      the specified file.
       MAILCHECK
	      Specifies	 how  often  (in  seconds)  bash checks for mail.  The
	      default is 60 seconds.  When it is time to check for  mail,  the
	      shell  does  so  before  displaying the primary prompt.  If this
	      variable is unset, or set to  a  value  that  is	not  a	number
	      greater than or equal to zero, the shell disables mail checking.
       MAILPATH
	      A colon-separated list of file names to  be  checked  for	 mail.
	      The message to be printed when mail arrives in a particular file
	      may be specified by separating the file name  from  the  message
	      with a `?'.  When used in the text of the message, $_ expands to
	      the name of the current mailfile.	 Example:
	      MAILPATH='/var/mail/bfox?"You  have  mail":~/shell-mail?"$_  has
	      mail!"'
	      Bash  supplies  a default value for this variable, but the loca-
	      tion of the user mail files that it  uses	 is  system  dependent
	      (e.g., /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
	      the getopts builtin command (see SHELL BUILTIN COMMANDS  below).
	      OPTERR  is  initialized to 1 each time the shell is invoked or a
	      shell script is executed.
       PATH   The search path for commands.  It is a colon-separated  list  of
	      directories  in  which the shell looks for commands (see COMMAND
	      EXECUTION below).	 The default path is system-dependent, and  is
	      set  by  the administrator who installs bash.  A common value is
	      ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:.''.
       POSIXLY_CORRECT
	      If this variable is in the environment  when  bash  starts,  the
	      shell  enters posix mode before reading the startup files, as if
	      the --posix invocation option had been supplied.	If it  is  set
	      while  the  shell is running, bash enables posix mode, as if the
	      command set -o posix had been executed.
       PROMPT_COMMAND
	      If set, the value is executed as a command prior to issuing each
	      primary prompt.
       PS1    The  value  of  this parameter is expanded (see PROMPTING below)
	      and used as the primary prompt string.   The  default  value  is
	      ``\s-\v\$ ''.
       PS2    The  value of this parameter is expanded as with PS1 and used as
	      the secondary prompt string.  The default is ``> ''.
       PS3    The value of this parameter is used as the prompt for the select
	      command (see SHELL GRAMMAR above).
       PS4    The  value  of  this  parameter  is expanded as with PS1 and the
	      value is printed before each command  bash  displays  during  an
	      execution	 trace.	 The first character of PS4 is replicated mul-
	      tiple times, as necessary, to indicate multiple levels of	 indi-
	      rection.	The default is ``+ ''.
       TIMEFORMAT
	      The  value of this parameter is used as a format string specify-
	      ing how the timing information for pipelines prefixed  with  the
	      time  reserved word should be displayed.	The % character intro-
	      duces an escape sequence that is expanded to  a  time  value  or
	      other  information.  The escape sequences and their meanings are
	      as follows; the braces denote optional portions.
	      %%	A literal %.
	      %[p][l]R	The elapsed time in seconds.
	      %[p][l]U	The number of CPU seconds spent in user mode.
	      %[p][l]S	The number of CPU seconds spent in system mode.
	      %P	The CPU percentage, computed as (%U + %S) / %R.

	      The optional p is a digit specifying the precision,  the	number
	      of fractional digits after a decimal point.  A value of 0 causes
	      no decimal point or fraction to be output.  At most three places
	      after  the  decimal  point may be specified; values of p greater
	      than 3 are changed to 3.	If p is not specified, the value 3  is
	      used.

	      The  optional l specifies a longer format, including minutes, of
	      the form MMmSS.FFs.  The value of p determines  whether  or  not
	      the fraction is included.

	      If  this	variable  is not set, bash acts as if it had the value
	      $'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'.  If the value is null,  no
	      timing  information  is  displayed.  A trailing newline is added
	      when the format string is displayed.

       TMOUT  If set to a value greater than zero, TMOUT  is  treated  as  the
	      default timeout for the read builtin.  The select command termi-
	      nates if input does not arrive after TMOUT seconds when input is
	      coming  from  a terminal.	 In an interactive shell, the value is
	      interpreted as the number of seconds to  wait  for  input	 after
	      issuing  the  primary prompt.  Bash terminates after waiting for
	      that number of seconds if input does not arrive.

       auto_resume
	      This variable controls how the shell interacts with the user and
	      job  control.   If this variable is set, single word simple com-
	      mands without redirections are treated as candidates for resump-
	      tion of an existing stopped job.	There is no ambiguity allowed;
	      if there is more than one job beginning with the	string	typed,
	      the  job	most  recently	accessed  is  selected.	 The name of a
	      stopped job, in this context, is the command line used to	 start
	      it.   If	set to the value exact, the string supplied must match
	      the name of a stopped job exactly;  if  set  to  substring,  the
	      string  supplied	needs  to  match  a substring of the name of a
	      stopped job.  The substring value provides functionality	analo-
	      gous  to the %?  job identifier (see JOB CONTROL below).	If set
	      to any other value, the supplied string must be a	 prefix	 of  a
	      stopped job's name; this provides functionality analogous to the
	      % job identifier.

       histchars
	      The two or three characters which control history expansion  and
	      tokenization (see HISTORY EXPANSION below).  The first character
	      is the history expansion character, the character which  signals
	      the  start  of  a	 history  expansion, normally `!'.  The second
	      character is the quick substitution character, which is used  as
	      shorthand	 for  re-running the previous command entered, substi-
	      tuting one string for another in the command.   The  default  is
	      `^'.   The optional third character is the character which indi-
	      cates that the remainder of the line is a comment when found  as
	      the  first  character of a word, normally `#'.  The history com-
	      ment character causes history substitution to be skipped for the
	      remaining	 words on the line.  It does not necessarily cause the
	      shell parser to treat the rest of the line as a comment.

   Arrays
       Bash provides one-dimensional array variables.	Any  variable  may  be
       used as an array; the declare builtin will explicitly declare an array.
       There is no maximum limit on the size of an array, nor any  requirement
       that  members  be indexed or assigned contiguously.  Arrays are indexed
       using integers and are zero-based.

       An array is created automatically if any variable is assigned to	 using
       the  syntax  name[subscript]=value.   The  subscript  is	 treated as an