ksh.man

一个开放源代码的 AT&T 的 Korn Shell 的复制品, 支持大多数 ksh89 的特性。

the shell to recognize a parameter assignment.
The fourth way of setting a parameter is with the \fBexport\fP, \fBreadonly\fP
and \fBtypeset\fP commands; see their descriptions in the Command Execution
section.
Fifth, \fBfor\fP and \fBselect\fP loops set parameters as well as
the \fBgetopts\fP, \fBread\fP and \fBset \-A\fP commands.
Lastly, parameters can be assigned values using assignment operators
inside arithmetic expressions (see Arithmetic Expressions below) or
using the \fB${\fP\fIname\fP\fB=\fP\fIvalue\fP\fB}\fP form
of parameter substitution (see below).
.\"}}}
.PP
.\"{{{  environment
Parameters with the export attribute (set using the \fBexport\fP or
\fBtypeset \-x\fP commands, or by parameter assignments followed by simple
commands) are put in the environment (see \fIenviron\fP(5)) of commands
run by the shell as \fIname\fP\fB=\fP\fIvalue\fP pairs.
The order in which parameters appear in the environment of a command
is unspecified.
When the shell starts up, it extracts parameters and their values from its
environment and automatically sets the export attribute for those parameters.
.\"}}}
.\"{{{  ${name[:][-+=?]word}
.PP
Modifiers can be applied to the \fB${\fP\fIname\fP\fB}\fP form of parameter
substitution:
.IP \fB${\fP\fIname\fP\fB:-\fP\fIword\fP\fB}\fP
if \fIname\fP is set and not null, it is substituted, otherwise \fIword\fP is
substituted.
.IP \fB${\fP\fIname\fP\fB:+\fP\fIword\fP\fB}\fP
if \fIname\fP is set and not null, \fIword\fP is substituted, otherwise nothing is substituted.
.IP \fB${\fP\fIname\fP\fB:=\fP\fIword\fP\fB}\fP
if \fIname\fP is set and not null, it is substituted, otherwise it is
assigned \fIword\fP and the resulting value of \fIname\fP is substituted.
.IP \fB${\fP\fIname\fP\fB:?\fP\fIword\fP\fB}\fP
if \fIname\fP is set and not null, it is substituted, otherwise \fIword\fP
is printed on standard error (preceded by \fIname\fP:) and an error occurs
(normally causing termination of a shell script, function or \&.-script).
If word is omitted the string `parameter null or not set' is used instead.
.PP
In the above modifiers, the \fB:\fP can be omitted, in which case the
conditions only depend on \fIname\fP being set (as opposed to set and
not null).
If \fIword\fP is needed, parameter, command, arithmetic and tilde substitution
are performed on it; if \fIword\fP is not needed, it is not evaluated.
.\"}}}
.PP
The following forms of parameter substitution can also be used:
.\"{{{  ${#name}
.IP \fB${#\fP\fIname\fP\fB}\fP
The number of positional parameters if \fIname\fP is \fB*\fP, \fB@\fP or
is not specified,
or the length of the string value of parameter \fIname\fP.
.\"}}}
.\"{{{  ${#name[*]}, ${#name[@]}
.IP "\fB${#\fP\fIname\fP\fB[*]}\fP, \fB${#\fP\fIname\fP\fB[@]}\fP"
The number of elements in the array \fIname\fP.
.\"}}}
.\"{{{  ${name#pattern}, ${name##pattern}
.IP "\fB${\fP\fIname\fP\fB#\fP\fIpattern\fP\fB}\fP, \fB${\fP\fIname\fP\fB##\fP\fIpattern\fP\fB}\fP"
If \fIpattern\fP matches the beginning of the value of parameter \fIname\fP,
the matched text is deleted from the result of substitution.  A single
\fB#\fP results in the shortest match, two \fB#\fP's results in the
longest match.
.\"}}}
.\"{{{  ${name%pattern}, ${name%%pattern}
.IP "\fB${\fP\fIname\fP\fB%\fP\fIpattern\fP\fB}\fP, \fB${\fP\fIname\fP\fB%%\fP\fIpattern\fP\fB}\fP"
Like \fB${\fP..\fB#\fP..\fB}\fP substitution, but it deletes from the end of the
value.
.\"}}}
.\"{{{  special shell parameters
.PP
The following special parameters are implicitly set by the shell and cannot be
set directly using assignments:
.\"{{{  !
.IP \fB!\fP
Process id of the last background process started.  If no background
processes have been started, the parameter is not set.
.\"}}}
.\"{{{  #
.IP \fB#\fP
The number of positional parameters (\fIi.e.\fP, \fB$1\fP, \fB$2\fP,
\fIetc.\fP).
.\"}}}
.\"{{{  $
.IP \fB$\fP
The process ID of the shell, or the PID of the original shell if
it is a subshell.
.\"}}}
.\"{{{  -
.IP \fB\-\fP
The concatenation of the current single letter options
(see \fBset\fP command below for list of options).
.\"}}}
.\"{{{  ?
.IP \fB?\fP
The exit status of the last non-asynchronous command executed.
If the last command was killed by a signal, \fB$?\fP is set to 128 plus
the signal number.
.\"}}}
.\"{{{  0
.IP "\fB0\fP"
The name the shell was invoked with (\fIi.e.\fP, \fBargv[0]\fP), or the
\fBcommand-name\fP if it was invoked with the \fB\-c\fP option and the
\fBcommand-name\fP was supplied, or the \fIfile\fP argument, if it was
supplied.
If the \fBposix\fP option is not set, \fB$0\fP is the name of the current
function or script.
.\"}}}
.\"{{{  1-9
.IP "\fB1\fP ... \fB9\fP"
The first nine positional parameters that were supplied to the shell,
function or \fB.\fP-script.
Further positional parameters may be accessed using
\fB${\fP\fInumber\fP\fB}\fP.
.\"}}}
.\"{{{  *
.IP \fB*\fP
All positional parameters (except parameter 0), 
\fIi.e.\fP, \fB$1 $2 $3\fP....
If used outside of double quotes, parameters are separate words
(which are subjected to word splitting); if used within double quotes,
parameters are separated by the first character of the \fBIFS\fP parameter
(or the empty string if \fBIFS\fP is null).
.\"}}}
.\"{{{  @
.IP \fB@\fP
Same as \fB$*\fP, unless it is used inside double quotes, in which case
a separate word is generated for each positional parameter \- if there
are no positional parameters, no word is generated ("$@" can be used
to access arguments, verbatim, without loosing null arguments or
splitting arguments with spaces).
.\"}}}
.\"}}}
.\"{{{  general shell parameters
.PP
The following parameters are set and/or used by the shell:
.\"{{{  _
.ksh(
.IP "\fB_\fP \fI(underscore)\fP"
When an external command is executed by the shell, this parameter is
set in the environment of the new process to the path of the executed
command.
In interactive use, this parameter is also set in the parent shell to
the last word of the previous command.
When \fBMAILPATH\fP messages are evaluated, this parameter contains
the name of the file that changed (see \fBMAILPATH\fP parameter below).
.ksh)
.\"}}}
.\"{{{  CDPATH
.IP \fBCDPATH\fP
Search path for the \fBcd\fP built-in command.  Works the same way as
\fBPATH\fP for those directories not beginning with \fB/\fP in \fBcd\fP
commands.
Note that if CDPATH is set and does not contain \fB.\fP nor an empty path,
the current directory is not searched.
.\"}}}
.\"{{{  COLUMNS
.IP \fBCOLUMNS\fP
Set to the number of columns on the terminal or window.
Currently set to the \fBcols\fP value as reported by \fIstty\fP(1) if that
value is non-zero.
This parameter is used by the interactive line editing modes, and by
\fBselect\fP, \fBset \-o\fP and \fBkill \-l\fP commands
to format information in columns.
.\"}}}
.\"{{{  EDITOR
.ksh(
.IP \fBEDITOR\fP
If the \fBVISUAL\fP parameter is not set, this parameter controls the
command line editing mode for interactive shells.
See \fBVISUAL\fP parameter below for how this works.
.ksh)
.\"}}}
.\"{{{  ENV
.IP \fBENV\fP
If this parameter is found to be set after any profile files are
executed, the expanded value is used as a shell start-up file.  It
typically contains function and alias definitions.
.\"}}}
.\"{{{  ERRNO
.IP \fBERRNO\fP
Integer value of the shell's errno variable \(em indicates the reason
the last system call failed.
.\" todo: ERRNO variable
.sp
Not implemented yet.
.\"}}}
.\"{{{  EXECSHELL
.IP \fBEXECSHELL\fP
If set, this parameter is assumed to contain the shell that is to be
used to execute commands that \fIexecve\fP(2) fails to execute and
which do not start with a `\fB#!\fP \fIshell\fP' sequence.
.\"}}}
.\"{{{  FCEDIT
.IP \fBFCEDIT\fP
The editor used by the \fBfc\fP command (see below).
.\"}}}
.\"{{{  FPATH
.IP \fBFPATH\fP
Like \fBPATH\fP, but used when an undefined function is executed to locate
the file defining the function.
It is also searched when a command can't be found using \fBPATH\fP.
See Functions below for more information.
.\"}}}
.\"{{{  HISTFILE
.ksh(
.IP \fBHISTFILE\fP
The name of the file used to store history.
When assigned to, history is loaded from the specified file.
Also, several invocations of the
shell running on the same machine will share history if their
\fBHISTFILE\fP parameters all point at the same file.
.br
NOTE: if HISTFILE isn't set, no history file is used.  This is
different from the original Korn shell, which uses \fB$HOME/.sh_history\fP;
in future, pdksh may also use a default history file.
.ksh)
.\"}}}
.\"{{{  HISTSIZE
.ksh(
.IP \fBHISTSIZE\fP
The number of commands normally stored for history, default 128.
.ksh)
.\"}}}
.\"{{{  HOME
.IP \fBHOME\fP
The default directory for the \fBcd\fP command and the value
substituted for an unqualified \fB~\fP (see Tilde Expansion below).
.\"}}}
.\"{{{  IFS
.IP \fBIFS\fP
Internal field separator, used during substitution and by the \fBread\fP
command, to split values into distinct arguments; normally set to
space, tab and newline.  See Substitution above for details.
.br
\fBNote:\fP this parameter is not imported from the environment
when the shell is started.
.\"}}}
.\"{{{  KSH_VERSION
.ksh(
.IP \fBKSH_VERSION\fP
The version of shell and the date the version was created (readonly).
See also the version commands in Emacs Editing Mode
and Vi Editing Mode sections, below.
.ksh)
.\"}}}
.\"{{{  SH_VERSION
.sh(
.IP \fBSH_VERSION\fP
The version of shell and the date the version was created (readonly).
.sh)
.\"}}}
.\"{{{  LINENO
.IP \fBLINENO\fP
The line number of the function or shell script that is currently being
executed.
.\"}}}
.\"{{{  LINES
.IP \fBLINES\fP
Set to the number of lines on the terminal or window.
.\"Currently set to the \fBrows\fP value as reported by \fIstty\fP(1) if that
.\"value is non-zero.
.\" todo: LINES variable
.sp
Not implemented yet.
.\"}}}
.\"{{{  MAIL
.ksh(
.IP \fBMAIL\fP
If set, the user will be informed of the arrival of mail in the named
file.  This parameter is ignored if the \fBMAILPATH\fP parameter is set.
.ksh)
.\"}}}
.\"{{{  MAILCHECK
.ksh(
.IP \fBMAILCHECK\fP
How often, in seconds, the shell will check for mail in the file(s)
specified by \fBMAIL\fP or \fBMAILPATH\fP.  If 0, the shell checks
before each prompt.  The default is 600 (10 minutes).
.ksh)
.\"}}}
.\"{{{  MAILPATH
.ksh(
.IP \fBMAILPATH\fP
A list of files to be checked for mail.  The list is colon separated,
and each file may be followed by a \fB?\fP and a message to be printed
if new mail has arrived.  Command, parameter and arithmetic substitution is
performed on the message, and, during substitution, the parameter \fB$_\fP
contains the name of the file.
The default message is \fByou have mail in $_\fP.
.ksh)
.\"}}}
.\"{{{  OLDPWD
.IP \fBOLDPWD\fP
The previous working directory.
Unset if \fBcd\fP has not successfully changed directories since the
shell started, or if the shell doesn't know where it is.
.\"}}}
.\"{{{  OPTARG
.IP \fBOPTARG\fP
When using \fBgetopts\fP, it contains the argument for a parsed option,
if it requires one.
.\"}}}
.\"{{{  OPTIND
.IP \fBOPTIND\fP
The index of the last argument processed when using \fBgetopts\fP.
Assigning 1 to this parameter causes \fBgetopts\fP to
process arguments from the beginning the next time it is invoked.
.\"}}}
.\"{{{  PATH
.IP \fBPATH\fP
A colon separated list of directories that are searched when looking