ksh.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\"
.ds OK [\|
.ds CK \|]
.\".de P
.TH ksh 1
.SH Name
ksh, rksh \- KornShell, a
standard/restricted command and programming language
.SH Syntax
.B ksh
[
.B \(+-aefhikmnoprstuvx
] [
.B \(+-o
option ] .\|.\|.
[
.B \-c
string ]
[ arg .\|.\|. ]
.br
.B rksh
[
.B \(+-aefhikmnoprstuvx
] [
.B \(+-o
option ] .\|.\|.
[
.B \-c
string ]
[ arg .\|.\|. ]
.SH Description
The 
.PN ksh
shell is a command and programming language
that executes commands read from a terminal
or a file.
The rksh
shell is a restricted version of the 
command interpreter
.IR ksh ;
it is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
See
.B Invocation
for the meaning of arguments to the shell.
.SS Definitions
A metacharacter is one of the following characters:
.RS
.PP
\fB;   &   (   )   \(bv   <   >   new-line   space   tab\fP
.RE
.PP
A blank is a
.B tab
or a
.BR space .
An identifier
is a sequence of letters, digits, or underscores
starting with a letter or underscore.
Identifiers are used as names for
functions and `named parameters'.
A word is a sequence of
characters separated by one or more non-quoted
metacharacters.
.PP
A command
is a sequence of characters in the syntax
of the shell language.
The shell reads each command and
carries out the desired action either directly or by invoking
separate utilities.
A special command is a command that is carried out by the
shell without creating a separate process.
Except for documented
side effects, most special commands can be implemented as separate
utilities.
.SS Commands
A simple-command is a sequence of blank
separated words
which may be preceded by a parameter assignment list.
See
.B Environment
below.
The first word specifies the name of the command to
be executed.
Except as specified below,
the remaining words are passed as arguments
to the invoked command.
The command name is passed as argument 0
(see
.MS exec 2 ).
The value of a simple-command is its exit status
if it terminates normally, or (octal) 200+\fIstatus\^\fP if
it terminates abnormally (see
.MS signal 2
for a list of
status values).
.PP
A pipeline
is a sequence of one or more
commands
separated by
.BR \(bv .
The standard output of each command but the last
is connected by a
.MS pipe 2
to the standard input of the next command.
Each command is run as a separate process;
the shell waits for the last command to terminate.
The exit status of a pipeline is the exit
status of the last command.
.PP
A list
is a sequence of one or more
pipelines
separated by
.BR ; ,
.BR & ,
.BR && ,
or
.BR \(bv\|\(bv ,
and optionally terminated by
.BR ; ,
.BR & ,
or
.BR \(bv& .
Of these five symbols,
.BR ; ,
.BR & ,
and
.BR \(bv&
have equal precedence,
which is lower than that of
.B &&
and
.BR \(bv\|\(bv .
The symbols
.B &&
and
.B \(bv\|\(bv
also have equal precedence.
A semicolon
.RB ( ; )
causes sequential execution of the preceding pipeline; an ampersand
.RB ( & )
causes asynchronous execution of the preceding pipeline (that is, the shell does
not wait for that pipeline to finish).  The symbol
.B \(bv&
causes asynchronous execution of the preceding command or pipeline
with a two-way pipe established to the parent shell.
The standard input and output of the spawned command
can be written to and read from by the parent Shell
using the
.B \-p
option of the special commands read and print described later.  The symbol
.B &&
.RB (\| \(bv\|\(bv )
causes the list following it to be executed only if the preceding pipeline
returns a zero (non-zero) value.
An arbitrary number of new-lines may appear in a
list, instead of a semicolon,
to delimit a command.
.PP
A command
is either a simple-command
or one of the following.
Unless otherwise stated,
the value returned by a command is that of the
last simple-command executed in the command.
.TP
\fBfor\fP \fIidentifier\^\fP \*(OK \fBin\fP \fIword\^\fP .\|.\|. \*(CK \fB;do\fP \fIlist\^\fP \fB;done\fP
Each time a
.B for
command is executed, 
.I identifier 
is set to the next 
.I word 
taken from the
.B in
.I word list.
If
.B in 
.I word
\&.\|.\|.
is omitted, then the
.B for
command executes the \fBdo\fP \fIlist\^\fP once for each positional parameter
that is set
(see
.B "Parameter Substitution"\fR).
Execution ends when there are no more words in the list.
.TP
\fBselect\fP \fIidentifier\^\fP \*(OK \fBin\fP \fIword\^\fP .\|.\|. \*(CK \fB;do\fP \fIlist\^\fP \fB;done\fP
A
.B select
command prints on standard error (file descriptor 2), the set of
.IR word s,
each preceded by a number.
If
.BI in " word"
\&.\|.\|.
is omitted, then the positional parameters are used instead
(see
.B "Parameter Substitution"
below).
The PS3 prompt is printed
and a line is read from the standard input.
If this line consists of the number
of one of the listed
.IR word s,
then the value of the parameter
.I identifier
is set to the
.I word
corresponding to this number.
If this line is empty the selection list is
printed again.
Otherwise the value of the parameter
.I identifier
is set to null.  The contents of the line read from standard input is
saved in the parameter REPLY.  The
.I list
is executed for each selection until a
break or end-of-file is encountered.
.TP
\fBcase\fP \fIword\^\fP \fBin\fP \*(OK \*(OK\fB(\fP\*(CK\fIpattern\^\fP \*(OK \(bv \fIpattern\^\fP \*(CK .\|.\|. \fB)\fP \fIlist\^\fP \fB;;\fP \*(CK .\|.\|. \fBesac\fP
A
.B case
command executes the
.I list
associated with the first
.I pattern
that matches
.IR word .
The form of the patterns is
the same as that used for
file-name generation (see
.B "File Name Generation"
below).
.TP
\fBif\fP \fIlist\^\fP \fB;then\fP \fIlist\^\fP \*(OK \
\fBelif\fP \fIlist\^\fP \fB;then\fP \fIlist\^\fP \*(CK .\|.\|. \
\*(OK \fB;else\fP \fIlist\^\fP \*(CK \fB;f\&i\fP
The
.I list
following \fBif\fP is executed and,
if it
returns a zero exit status, the
.I list
following the first
.B then
is executed.  Otherwise, the
.I list
following \fBelif\fP
is executed and, if its value is zero, the
.I list
following the next
.B then
is executed.  Failing that, the
.B else
.I list
is executed.  If no
.B else
.I list
or
.B then
.I list
is executed, then the
.B if
command returns a zero exit status.
.TP
.PD 0
\fBwhile\fP \fIlist\^\fP \fB;do\fP \fIlist\^\fP \fB;done\fP
.TP
\fBuntil\fP \fIlist\^\fP \fB;do\fP \fIlist\^\fP \fB;done\fP
.PD
A
.B while
command repeatedly executes the
.B while
.I list
and, if the exit status of the last command in the list is zero, executes
the
.B do
.IR list ;
otherwise the loop terminates.
If no commands in the
.B do
.I list
are executed, then the
.B while
command returns a zero exit status;
.B until
may be used in place of
.B while
to negate
the loop termination test.
.TP
\fB(\fP\fIlist\^\fP\fB)\fP
Execute
.I list
in a separate environment.
Note, that if two adjacent open parentheses are
needed for nesting, a space must be inserted to avoid
arithmetic evaluation as described below.
.TP
\fB{ \fP\fIlist\^\fP\fB;}\fP
The 
.I list
is simply executed.
Note that unlike the metacharacters
.B (
and
.BR ) ,
.br
.B {
and
.B }
are `reserved words' and must at the beginning of a line or after a
.B ;
in order to be recognized.
.TP
\fB[[\fP\fIexpression\^\fP\fB]]\fP
Evaluates
.I expression
and returns a zero exit status when
.I expression
is true.
See
.B "Conditional Expressions"
for a description of
.IR expression.
.TP
.PD 0
\fBfunction\fP \fIidentifier\^\fP \fB{\fP \fIlist\^\fP \fB;}\fP
.TP
\fIidentifier\^\fP \fB() {\fP \fIlist\^\fP \fB;}\fP
.PD
Define a function which is referenced by
.IR identifier .
The body of the function is the
.I list
of commands between
.B {
and
.BR } .
(See
.B Functions
below).
.TP
\fBtime \fP\fIpipeline\^\fP
.br
The
.I pipeline
is executed and the elapsed time as well as
the user and system time are printed on standard error.
.PP
The following reserved words
are only recognized as the first word of a command
and when not quoted:
.if t .RS
.PP
.B
.if n if then else elif fi case esac for while until do done { } function select time [[ ]]
.if t if   then   else   elif   fi   case   esac   for   while   until   do   done   {   }   function   select   time  [[  ]]
.if t .RE
.SS Comments
A word beginning with
.B #
causes that word and all the following characters up to a new-line
to be ignored.
.SS Aliasing
The first word of each command is replaced by the text of an
alias if an alias for this word has been defined.  The
first character of an alias
name can be any non-special printable character,
but the rest of the characters
must be the same as for a valid identifier.
The replacement string can contain any
valid Shell script
including the metacharacters listed above.
The first word of each command in the
replaced text,
other than
any that are in the process of being replaced,
will be tested for aliases.
If the last character of the alias value is a blank
then the word following the alias will also be checked for alias
substitution.
Aliases can be used to redefine special
builtin commands but cannot be used to redefine
the reserved words listed above.
Aliases can be created, listed, and exported with the
.PN alias
command and can be removed with the
.PN unalias
command.
Exported aliases remain in effect for
scripts invoked by name,
but must be reinitialized for separate invocations
of the Shell (See
.B Invocation
below).
.PP
Aliasing is performed when
scripts are read,
not while they are executed.
Therefore,
for an alias to take effect
the alias definition command has to be executed before
the command which references the alias is read.
.PP
Aliases are frequently used as a short hand for full path
names.
An option to the aliasing facility allows the value of the alias
to be automatically set to the full pathname of
the corresponding command.  These aliases are called
tracked aliases.  The value of a tracked
alias is defined the first time the corresponding command
is looked up and becomes undefined each time
the PATH variable is reset.  These aliases remain
tracked so that the next
subsequent reference will redefine the value.
Several tracked aliases are compiled into the shell.
The
.B \-h
option of the
.PN set
command makes each referenced command name
into a tracked alias.
.PP
The following
`exported aliases'
are compiled into the shell
but can be unset or redefined:
.RS 5
.PD 0
.TP
.B "autoload=\(fmtypeset \-fu\(fm"
.TP
.B "false=\(fmlet 0\(fm"
.TP
.B "functions=\(fmtypeset \-f\(fm"
.TP
.B "hash=\(fmalias \-t\(fm"
.TP
.B "history=\(fmfc \-l\(fm"
.TP
.B "integer=\(fmtypeset \-i\(fm"
.TP
.B "nohup=\(fmnohup \(fm"
.TP
.B "r=\(fmfc \-e \-\(fm"
.TP
.B "true=\(fm:\(fm"
.TP
.B "type=\(fmwhence \-v\(fm"
.PD
.RE
.SS Tilde Substitution
After alias substitution is performed, each word
is checked to see if it begins with an unquoted
.BR \(ap .
If it does, then the word up to a
.B /
is checked to see if it matches a user name in the
.PN /etc/passwd
file.
If a match is found, the
.B \(ap
and the matched login name is replaced by the
login directory of the matched user.
This is called a
`tilde substitution'.
If no match is found, the original text is left unchanged.
A
.B \(ap
by itself, or in front of a
.BR / ,
is replaced by the value of the HOME parameter.
A
.B \(ap
followed by a
.B +
or
.B \-
is replaced by $PWD and $OLDPWD respectively.
.PP
In addition, tilde substitution is attempted when
the value of a `variable assignment parameter'
begins with a
.BR \(ap .
.SS Command Substitution
The standard output from a command enclosed in
parentheses preceded by a dollar sign (
.B $(\|)
)
or a pair of grave accents
.Pn ( `` )
may be used as part or all
of a word;
trailing new-lines are removed.
In the second (archaic) form, the string between the quotes is processed
for special quoting characters before the command is executed. (See
.BR Quoting ).
The command substitution
\^\fB$(\^cat file\^)\fP\^
can be replaced by the equivalent but faster
\^\fB$(\^<file\^)\fP\^.
Command substitution of most special commands
that do not perform input/output redirection are
carried out without creating a separate process.
.PP
An arithmetic expression enclosed in double
parenthesis preceded by a dollar sign (
.B $((\|))
)
is replaced by the value of the arithmetic expression
within the double parenthesis.
.SS Process Substitution.
This feature is only available on
versions of the operating system that support the
.PN /dev/fd
directory for naming open files.
Each command argument of the form
\fB<(\fP\fIlist\^\fP\fB)\fP
or
\fB>(\fP\fIlist\^\fP\fB)\fP
will run process
.I list
asynchronously connected to some file in
.PN /dev/fd .
The name of this file will become the argument to the command.
If the form with
.B >
is selected then writing on this file will provide input for
.IR list .
If
.B <
is used,
then the file passed as an argument will contain the output of the
.I list
process.
For example,
.RS
.PP
\fBpaste <(cut \-f1\fP \fIfile1\fP\fB) <(cut \-f3\fP \fIfile2\fB) | tee >(\fP\fIprocess1\fP\fB) >(\fP\fIprocess2\fP\fB)\fP
.RE
.PP
.BR cut s
fields 1 and 3 from
the files
.I file1
and
.I file2
respectively,
.BR paste s
the results together, and sends it to the processes
.I process1
and
.IR process2 ,
as well as putting it onto the standard output.
Note that the file, which is passed as an argument to the command,
is a system
.PN pipe 
so programs that expect to
.PN lseek
on the file will not work.
.SS Parameter Substitution
A parameter is an identifier,
one or more digits,
or any of the characters
.BR \(** ,
.BR @ ,
.BR # ,
.BR ? ,
.BR \- ,
.BR $ ,
and
.BR !\\^ .
A `named parameter' (a parameter denoted by an identifier)
has a value and zero or more attributes.
Named parameters can be assigned values and attributes
by using the
.PN typeset
special command.
The attributes supported by the Shell are described
later with the
.PN typeset
special command.
Exported parameters pass values and attributes to
the environment.
.PP
The shell supports a one-dimensional array facility.
An element of an array parameter is referenced by a
subscript.
A subscript is denoted by a
.BR [ ,
followed by an
`arithmetic expression'
(see 
.B Arithmetic Evaluation)
followed by a
.BR ] .
To assign values to an array, use
\fBset \-A\fP \fIname\fP  \fIvalue\fP .\|.\|. .
The value of all
subscripts must be in the
range of