ksh.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

0 through 1023.
Arrays need not be declared.
Any reference to a named parameter
with a valid subscript is
legal and an array will be created if necessary.
Referencing an array without a subscript
is equivalent to referencing the element zero.
.PP
The
.I value
of a
.IR name d 
parameter may also be assigned by writing:
.RS
.PP
.IB name = value\^\|
\*(OK
.IB name = value
\*(CK .\|.\|.
.RE
.PP
.PD 0
If the integer attribute,
.BR \-i ,
is set for
.I name
the
.I value
is subject to arithmetic evaluation as described below.
.PP
Positional parameters,
parameters denoted by a number,
may be assigned values with the
.PN set
special command.  Parameter $0
is set from argument zero when the shell
is invoked.
.PP
The character
.B $
is used to introduce substitutable
.IR parameters .
.TP
\fB${\fP\fIparameter\^\fP\fB}\fP
The shell
reads all the characters from
.B ${
to the matching
.B }
as part of the same word even if it contains
braces or metacharacters.
The value, if any, of the parameter is substituted.
The braces are required when
.I parameter
is followed by a letter, digit, or underscore
that is not to be interpreted as part of its name
or when a named parameter is subscripted.
If
.I parameter
is one or more digits then it is a positional parameter.
A positional parameter of more than one digit must be
enclosed in braces.
If
.I parameter
is
.BR \(**
or
.BR @ ,
then all the positional
parameters, starting with
.BR $1 ,
are substituted
(separated by a field separator character).
If an array
.I identifier
with subscript
.B \(**
or
.B @
is used,
then the value
for each of the
elements
is substituted
(separated by a field separator character).
.TP
\fB${#\fP\fIparameter\^\fP\fB}\fP
If
.I parameter
is
.B \(**
or
.BR @ ,
the number of positional parameters is substituted.
Otherwise, the length of the value of the
.I parameter
is substituted.
.TP
\fB${#\fP\fIidentifier\fP\fB[*]}\fP
The number of elements in the array
.I identifier
is substituted.
.TP
\fB${\fP\fIparameter\^\fP\fB:\-\fP\fIword\^\fP\fB}\fP
If
.I parameter
is set and is non-null then substitute its value;
otherwise substitute
.IR word .
.TP
\fB${\fP\fIparameter\^\fP\fB:=\fP\fIword\^\fP\fB}\fP
If
.I parameter
is not set or is null then set it to
.IR word ;
the value of the parameter is then substituted.
Positional parameters may not be assigned to
in this way.
.TP
\fB${\fP\fIparameter\^\fP\fB:?\fP\fIword\^\fP\fB}\fP
If
.I parameter
is set and is non-null then substitute its value;
otherwise, print
.I word
and exit from the shell.
If
.I word
is omitted then a standard message is printed.
.TP
\fB${\fP\fIparameter\^\fP\fB:+\fP\fIword\^\fP\fB}\fP
If
.I parameter
is set and is non-null then substitute
.IR word ;
otherwise substitute nothing.
.TP
.PD 0
\fB${\fP\fIparameter\^\fP\fB#\fP\fIpattern\^\fP\fB}\fP
.TP
\fB${\fP\fIparameter\^\fP\fB##\fP\fIpattern\^\fP\fB}\fP
.PD
If
the Shell
.I pattern
matches the beginning of the value of
.IR parameter ,
then the value of
this substitution is the value of the
.I parameter
with the matched portion deleted;
otherwise the value of this
.I parameter
is substituted.
In the first form the smallest matching pattern is deleted and in the
second form the largest matching pattern is deleted.
.TP
.PD 0
\fB${\fP\fIparameter\^\fP\fB%\fP\fIpattern\^\fP\fB}\fP
.TP
\fB${\fP\fIparameter\^\fP\fB%%\fP\fIpattern\^\fP\fB}\fP
.PD
If
the Shell
.I pattern
matches the end of the value of
.IR parameter ,
then the value of
this substitution is the value of the
.I parameter
with the matched part deleted;
otherwise substitute the value of
.IR parameter .
In the first form the smallest matching pattern is deleted and in the
second form the largest matching pattern is deleted.
.PD
.PP
In the above,
.I word
is not evaluated unless it is
to be used as the substituted string,
so that, in the following example,
.PN pwd
is executed only if
.B d
is not set or is null:
.RS
.PP
.B "echo \|${d:\-\^$(\^pwd\^)\^}"
.RE
.PP
If the colon (
.B : )
is omitted from the above expressions,
then the shell only checks whether
.I parameter
is set or not.
.PP
The following parameters are automatically set by the shell:
.RS
.PD 0
.TP 10
.B #
The number of positional parameters in decimal.
.TP
.B \-
Flags supplied to the shell on invocation or by
the
.PN set
command.
.TP
.B ?
The decimal value returned by the last executed command.
.TP
.B $
The process number of this shell.
.TP
.B _
Initially, the value
.B _
is an absolute pathname of the shell or script being executed
as passed in the
.IR environment .
Subsequently it is assigned the last argument of the previous command.
This parameter is not set for commands which are asynchronous.
file when checking for mail.
.TP
.B !
The process number of the last background command invoked.
.TP
.SM ERRNO
The value of errno as set by the most recently failed system call.
This value
is system dependent and is intended for debugging purposes.
.TP
.SM LINENO
The line number of the current line within the script or
function being executed.
.TP
.SM OLDPWD
The previous working directory set by the
.PN cd
command.
.TP
.SM OPTARG
The value of the last option argument processed by the
.PN getopts
special command.
.TP
.SM OPTIND
The index of the last option argument processed by the
.PN getopts
special command.
.TP
.SM PPID
The process number of the parent of the shell.
.TP
.SM PWD
The present working directory set by the
.PN cd
command.
.TP
.SM RANDOM
Each time this parameter is referenced, a random integer,
uniformly distributed between 0 and 32767, is generated.
The sequence of random numbers can be initialized by assigning
a numeric value to
RANDOM.
.TP
.SM REPLY
This parameter is set by the
.B select
statement and by
the
.B read
special command when no arguments are supplied.
.TP
.SM SECONDS
Each time this parameter is referenced, the number of
seconds since shell invocation is returned.
If this parameter is
assigned a value, then the value returned upon reference will
be the value that was assigned plus the number of seconds since the assignment.
.PD
.RE
.PP
The following parameters are used by the shell:
.RS
.PD 0
.TP
.SM CDPATH
The search path for the
.PN cd
command.
.TP
.SM COLUMNS
If this variable is set,
the value is used to define the width of the edit window
for the shell edit modes and for printing
.B select
lists.
.TP
.SM EDITOR
If the value of this variable ends in
.IR emacs ,
.IR gmacs ,
or
.I vi
and the
.SM VISUAL
variable is not set,
then the corresponding option
(see Special Command
.B set
below)
will be turned on.
.TP
.SM ENV
If this parameter is set, then
parameter substitution is performed on
the value to generate
the pathname of the script that will be
executed when the
.I shell
is invoked.
(See
.I Invocation
below.)
This file is typically used for
.I alias
and
.I function
definitions.
.TP
.SM FCEDIT
The default editor name for the
.B fc
command.
.TP
.SM FPATH
The search path for function definitions.
This path is searched when a function with the
.B \-u
attribute is referenced and when a command is not found.
If an executable file is found, then it is read and executed
in the current environment.
.TP
.SM IFS
Internal field separators,
normally
.BR space ,
.BR tab ,
and
.B new-line
that is used to separate command words which result from
command or parameter substitution
and for separating words with the special command
.BR read .
The first character of the
.SM IFS
parameter is used to separate arguments for the
.B "$\(**"
substitution (See
.I Quoting
below).
.TP
.SM
HISTFILE
If this parameter is set when the shell is invoked, then
the value is the pathname of the file that will be
used to store the command history.
(See
.I "Command re-entry"
below.)
.TP
.SM HISTSIZE
If this parameter is set when the shell is invoked, then
the number of previously entered commands that
are accessible by this shell
will be greater than or equal to this number.
The default is 128.
.TP
.SM HOME
The default argument (home directory) for the
.B cd
command.
.TP
.SM LINES
If this variable is set,
the value is used to determine the column length for printing
.B select
lists.
Select lists will print vertically until about two-thirds of
.SM LINES
lines are filled.
.TP
.SM LOGNAME
The name of the user's login account, corresponding to the login name
in the user database.
.TP
.SM MAIL
If this parameter is set to the name of a mail file
.I and
the
.SM MAILPATH
parameter is not set,
then the shell informs the user of arrival of mail
in the specified file.
.TP
.SM MAILCHECK
This variable specifies how often (in seconds) the
shell will check for changes in the modification time
of any of the files specified by the
.SM MAILPATH
or
.SM MAIL
parameters.
The default value is 600 seconds.
When the time has elapsed
the shell will check before issuing the next prompt.
.TP
.SM MAILPATH
A colon (
.B :
)
separated list of file names.
If this parameter is set
then the shell informs the user of
any modifications to the specified files
that have occurred within the last
.SM MAILCHECK
seconds.
Each file name can be followed by a
.B ?
and a message that will be printed.
The message will undergo parameter substitution
with the parameter,
.B $_
defined as the name of the file that has changed.
The default message is
.I you have mail in $_.
.TP
.SM PATH
The search path for commands (see
.I Execution
below).
The user may not change
.B \s-1PATH\s+1
if executing under
.PN rksh
(except in
.I .profile
).
.TP
.SM PS1
The value of this parameter is expanded for parameter
substitution to define the
primary prompt string which by default is
.RB `` "$ \|" ''.
The character
.B !
in the primary prompt string is replaced by the
.I command
number (see
.I Command Re-entry
below).
.TP
.SM PS2
Secondary prompt string, by default
.RB `` "> \|" ''.
.TP
.SM PS3
Selection prompt string
used within a
.B select
loop, by default
.RB `` "#? \|" ''.
.TP
.SM PS4
The value of this parameter is expanded for parameter
substitution and precedes each line of an execution trace.
If omitted, the execution trace prompt is
.RB `` "+ \|" ''.
.TP
.SM SHELL
The pathname of the
.I shell
is kept in the environment.
At invocation, if the basename of this variable matches the pattern
.BR *r*sh ,
then the shell becomes restricted.
.TP
.SM TMOUT
If set to a value greater than zero,
the shell will terminate if a command is not entered within
the prescribed number of seconds after issuing the
.SM PS1
prompt.
(Note that the shell can be compiled with a maximum bound
for this value which cannot be exceeded.)
.TP
.SM VISUAL
If the value of this variable ends in
.IR emacs ,
.IR gmacs ,
or
.I vi
then the corresponding option
(see Special Command
.B set
below)
will be turned on.
.PD
.RE
.PP
The shell gives default values to
\fB\s-1PATH\s+1\fP, \fB\s-1PS1\s+1\fP, \fB\s-1PS2\s+1\fP, \fB\s-1MAILCHECK\s+1\fP,
\fB\s-1TMOUT\s+1\fP and \fB\s-1IFS\s+1\fP,
while
.SM HOME,
.SM SHELL
.SM ENV
and
.SM MAIL
are
not set at all by the shell (although
.SM HOME
.I is
set by
.IR login (1)).
On some systems
.SM MAIL
and
.SM SHELL
are also
set by
.IR login (1)).
.SS Blank Interpretation.
After parameter and command substitution,
the results of substitutions are scanned for the field separator
characters (
those found in
.SM
.B IFS
)
and split into distinct arguments where such characters are found.
Explicit null arguments (\^\fB"\^"\fP or \fB\*\(fm\^\*\(fm\fP\^) are retained.
Implicit null arguments
(those resulting from
.I parameters
that have no values) are removed.
.SS File Name Generation.
Following substitution, each command
.I word
is scanned for
the characters
.BR \(** ,
.BR ? ,
and
.B \*(OK
unless the
.B \-f
option has been
.BR set .
If one of these characters appears
then the word is regarded as a
.IR pattern .
The word is replaced with lexicographically sorted file names that match the pattern.
If no file name is found that matches the pattern, then
the word is left unchanged.
When a
.I pattern
is used for file name generation,
the character
.B .
at the start of a file name
or immediately following a
.BR / ,
as well as the character
.B /
itself,
must be matched explicitly.
In other instances of pattern matching the
.B /
and
.B .
are not treated specially.
.PP
.PD 0
.RS
.TP
.B \(**
Matches any string, including the null string.
.TP
.B ?
Matches any single character.
.TP
.BR \*(OK \^.\|.\|.\^ \*(CK
Matches any one of the enclosed characters.
A pair of characters separated by
.B \-
matches any
character lexically between the pair, inclusive.
If the first character following the opening "[ \|"
is a "! \|" then any character not enclosed is matched.
A
.B \-
can be included in the character set by putting it as the
first or last character.