ksh.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.PD
.RE
A
.I pattern-list
is a list of one or more patterns separated by each other
with a
.BR \(bv .
Composite patterns can be formed with one or more of the following:
.PD 0
.RS
.TP
\fB?(\fP\fIpattern-list\^\fP\fB)\fP
Optionally matches any one of the given patterns.
.TP
\fB*(\fP\fIpattern-list\^\fP\fB)\fP
Matches zero or more occurrences of the given patterns.
.TP
\fB+(\fP\fIpattern-list\^\fP\fB)\fP
Matches one or more occurrences of the given patterns.
.TP
\fB\&@\&(\fP\fIpattern-list\^\fP\fB)\fP
Matches exactly one of the given patterns.
.TP
\fB!(\fP\fIpattern-list\^\fP\fB)\fP
Matches anything, except one of the given patterns.
.PD
.RE
.SS Quoting.
Each of the
.I metacharacters
listed above (See
.I Definitions
above)
has a special meaning to the shell
and causes termination of a word unless quoted.
A character may be
.I quoted
(that is, made to stand for itself)
by preceding
it with a
.BR \e .
The pair
.B \enew-line
is ignored.
All characters enclosed between a pair of single quote marks (\^\fB\(fm\^\(fm\fP\^),
are quoted.
A single quote cannot appear within single quotes.
Inside double quote marks
(\fB"\^"\fP),
parameter and command substitution occurs and
.B \e
quotes the characters
.BR \e ,
.BR \f(CW`\fP ,
\fB"\fP,
and
.BR $ .
The meaning of
.B "$\(**"
and
.B "$@"
is identical when not quoted or when used as a parameter assignment value
or as a file name.
However, when used as a command argument,
.B "$\(**"
is equivalent to
\fB"$1\fP\fId\fP\fB\|$2\fP\fId\fP\|.\|.\|.\fB"\fP,
where
.I d
is the first character of the
.SM
.B IFS
parameter, whereas
.B "$@"
is equivalent to
.B "$1"\|
"$2"\|
\&.\|.\|.\^.
Inside grave quote marks
.Pn ( `` )
.B \e
quotes the characters
.BR \e ,
.PN ` ,
and
.PP $ .
If the grave quotes occur within double quotes then
.BR \e
also quotes the character
\fB"\fP.
.PP
The special meaning of reserved words or aliases can be removed by quoting any
character of the reserved word.
The recognition of function names or special command names listed below
cannot be altered by quoting them.
.SS Arithmetic Evaluation.
An ability to perform integer arithmetic
is provided with the special command
.BR let .
Evaluations are performed using
.I long
arithmetic.
Constants are of the form
\*(OK\fIbase\fB#\^\fR\*(CK\fIn\^\fP
where
.I base
is a decimal number between two and thirty-six
representing the arithmetic base
and
.I n
is a number in that base.
If
.I base
is omitted
then base 10 is used.
.PP
An arithmetic expression uses the same syntax, precedence, and
associativity of
expression of the C language.
All the integral operators,
other than
.BR ++ ,
.BR \-\|\- ,
.BR ?: ,
and
.B ,
are supported.
Named parameters can be referenced by name within an arithmetic expression
without using the parameter substitution syntax.
When a named parameter is referenced, its value is evaluated as
an arithmetic expression. 
.PP
An internal integer representation of a
.I named parameter
can be specified with the
.B \-i
option of the
.B typeset
special command.
Arithmetic evaluation is performed on the value of each
assignment to a named parameter with the
.B \-i
attribute.
If you do not specify an arithmetic base,
the first assignment to the
parameter determines the arithmetic base.
This base is
used when
parameter substitution occurs.
.PP
Since many of the arithmetic operators require
quoting, an alternative form of the
.B let
command is provided.
For any command which begins with a
.BR (( ,
all the characters until a matching
.B ))
are treated as a quoted expression.
More precisely,
.BR (( .\|.\|. ))
is equivalent to
.B let
\fB"\fP\|.\|.\|.\fB"\fP.
.SS Prompting.
When used interactively,
the shell prompts with the value of
.SM
.B PS1
before reading a command.
If at any time a new-line is typed and further input is needed
to complete a command, then the secondary prompt
(that is, the value of
.BR \s-1PS2\s+1 )
is issued.
.SS Conditional Expressions.
A
.I "conditional expression"
is used with the
.B [[
compound command to test attributes of files and to compare
strings.
Word splitting and file name generation are
not performed on the words between
.B [[
and
.BR ]] .
Each expression can be constructed from one or more
of the following unary or binary expressions:
.PD 0
.TP
\fB\-a\fP \fIfile\fP
True, if
.I file
exists.
.TP
\fB\-b\fP \fIfile\fP
True, if
.I file
exists and is a block special file.
.TP
\fB\-c\fP \fIfile\fP
True, if
.I file
exists and is a character special file.
.TP
\fB\-d\fP \fIfile\fP
True, if
.I file
exists and is a directory.
.TP
\fB\-f\fP \fIfile\fP
True, if
.I file
exists and is an ordinary file.
.TP
\fB\-g\fP \fIfile\fP
True, if
.I file
exists and is has its setgid bit set.
.TP
\fB\-k\fP \fIfile\fP
True, if
.I file
exists and is has its sticky bit set.
.TP
\fB\-n\fP \fIstring\fP
True, if length of
.I string
is non-zero.
.TP
\fB\-o\fP \fIoption\fP
True, if option named
.I option
is on.
.TP
\fB\-p\fP \fIfile\fP
True, if
.I file
exists and is a fifo special file or a pipe.
.TP
\fB\-r\fP \fIfile\fP
True, if
.I file
exists and is readable by current process.
.TP
\fB\-s\fP \fIfile\fP
True, if
.I file
exists and has size greater than zero.
.TP
\fB\-t\fP \fIfildes\fP
True, if file descriptor number
.I fildes
is open and associated with a terminal device.
.TP
\fB\-u\fP \fIfile\fP
True, if
.I file
exists and is has its setuid bit set.
.TP
\fB\-w\fP \fIfile\fP
True, if
.I file
exists and is writable by current process.
.TP
\fB\-x\fP \fIfile\fP
True, if
.I file
exists and is executable by current process.
If
.I file
exists and is a directory, then the current process
has permission to search in the directory.
.TP
\fB\-z\fP \fIstring\fP
True, if length of
.I string
is zero.
.TP
\fB\-L\fP \fIfile\fP
True, if
.I file
exists and is a symbolic link.
.TP
\fB\-O\fP \fIfile\fP
True, if
.I file
exists and is owned by the effective user id of this process.
.TP
\fB\-G\fP \fIfile\fP
True, if
.I file
exists and its group matches the effective group id of this process.
.TP
\fB\-S\fP \fIfile\fP
True, if
.I file
exists and is a socket.
.TP
\fIfile1\fP \fB\-nt\fP \fIfile2\fP
True, if
.I file1
exists and is newer than
.IR file2 .
.TP
\fIfile1\fP \fB\-ot\fP \fIfile2\fP
True, if
.I file1
exists and is older than
.IR file2 .
.TP
\fIfile1\fP \fB\-ef\fP \fIfile2\fP
True, if
.I file1
and 
.I file2
exist and refer to the same file.
.TP
\fIstring\fP \fB=\fP \fIpattern\fP
True, if
.I string
matches
.IR pattern .
.TP
\fIstring\fP \fB!=\fP \fIpattern\fP
True, if
.I string
does not match
.IR pattern .
.TP
\fIstring1\fP \fB<\fP \fIstring2\fP
True, if
.I string1
comes before
.I string2
based on ASCII value of their characters.
.TP
\fIstring1\fP \fB>\fP \fIstring2\fP
True, if
.I string1
comes after
.I string2
based on ASCII value of their characters.
.TP
\fIexp1\fP \fB\-eq\fP \fIexp2\fP
True, if
.I exp1
is equal to
.IR exp2.
.TP
\fIexp1\fP \fB\-ne\fP \fIexp2\fP
True, if
.I exp1
is not equal to
.IR exp2.
.TP
\fIexp1\fP \fB\-lt\fP \fIexp2\fP
True, if
.I exp1
is less than
.IR exp2.
.TP
\fIexp1\fP \fB\-gt\fP \fIexp2\fP
True, if
.I exp1
is greater than
.IR exp2.
.TP
\fIexp1\fP \fB\-le\fP \fIexp2\fP
True, if
.I exp1
is less than or equal to
.IR exp2.
.TP
\fIexp1\fP \fB\-ge\fP \fIexp2\fP
True, if
.I exp1
is greater than or equal to
.IR exp2.
.PD
.PP
In each of the above expressions, if
.I file
is of the form
\fB/dev/fd/\fP\fIn\fP,
where
.I n
is an integer,
then the test applied to the open file whose
descriptor number is
.IR n .
.PP
A compound expression can be constructed from these primitives by
using any of the following, listed in decreasing order of precedence.
.PD 0
.TP
\fB(\fP\fIexpression\fP\fB)\fP
True, if
.I expression
is true.
Used to group expressions.
.TP
\fB!\fP \fIexpression\fP
True if
.I expression
is false.
.TP
\fIexpression1\fP \fB&&\fP \fIexpression2\fP
True, if
.I expression1
and
.I expression2
are both true.
.TP
\fIexpression1\fP \fB\(bv\(bv\fP \fIexpression2\fP
True, if either
.I expression1
or
.I expression2
is true.
.PD
.SS Input/output.
Before a command is executed, its input and output
may be redirected using a special notation interpreted by the shell.
The following may appear anywhere in a simple-command
or may precede or follow a
.I command
and are
.I not
passed on to the invoked command.
Command and parameter substitution occurs before
.I word
or
.I digit
is used except as noted below.
File name generation
occurs only if the pattern matches a single file
and blank interpretation is not performed.
.TP 14
.BI < word
Use file
.I word
as standard input (file descriptor 0).
.TP
.BI > word
Use file
.I word
as standard output (file descriptor 1).
If the file does not exist then it is created.
If the file exists, and the
.B noclobber
option is on,
this causes an error;
otherwise, it is truncated to zero length.
.TP
.BI >| word
Sames as
.BR > ,
except that it overrides the
.B noclobber
option.
.TP
.BI >> word
Use file
.I word
as standard output.
If the file exists then output is appended to it (by first seeking to the end-of-file);
otherwise, the file is created.
.TP
.BI <> word
Open file
.I word
for reading and writing
as standard input.
.TP
\fB<<\fP\*(OK\fB\-\fP\*(CK\fIword\fP
The shell input is read up to a line that is the same as
.IR word ,
or to an end-of-file.
No parameter substitution, command substitution or
file name generation is performed on
.IR word .
The resulting document,
called a
.IR here-document ,
becomes
the standard input.
If any character of
.I word
is quoted, then no interpretation
is placed upon the characters of the document;
otherwise, parameter and command substitution occurs,
.B \enew-line
is ignored,
and
.B \e
must be used to quote the characters
.BR \e ,
.BR $ ,
.Pn ` ,
and the first character of
.IR word .
If
.B \-
is appended to
.BR << ,
then all leading tabs are stripped from
.I word
and from the document.
.TP
.BI <& digit
The standard input is duplicated from file descriptor
.I digit
(see
.IR dup (2)).
Similarly for the standard output using
.BR >&
.IR digit .
.TP
.B <&\-
The standard input is closed.
Similarly for the standard output using
.BR >&\- .
.TP
.B <&p
The input from the co-process is moved to standard input.
.TP
.B >&p
The output to the co-process is moved to standard output.
.PP
If one of the above is preceded by a digit,
then the
file descriptor number referred to is that specified
by the digit
(instead of the default 0 or 1).
For example:
.RS
.PP
\&.\|.\|. \|2>&1
.RE
.PP
means file descriptor 2 is to be opened
for writing as a duplicate
of file descriptor 1.
.PP
The order in which redirections are specified is significant.
The shell evaluates each redirection in terms of the
.RI ( "file descriptor" ", " file )
association at the time of evaluation.
For example:
.RS
.PP
\&.\|.\|. \|1>\fIfname\^\fP 2>&1
.RE
.PP
first associates file descriptor 1 with file
.IR fname .
It then associates file descriptor 2 with the file associated with file
descriptor 1 (that is,
.IR fname ).
If the order of redirections were reversed, file descriptor 2 would be associated
with the terminal (assuming file descriptor 1 had been) and then file descriptor
1 would be associated with file
.IR fname .
.PP
If a command is followed by
.B &
and job control is not active,
then the default standard input
for the command
is the empty file
.BR /dev/null .
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by
input/output specifications.
.SS Environment.
The
.I environment
(see
.IR environ (7))
is a list of name-value pairs that is passed to
an executed program in the same way as a normal argument list.
The names must be
.I identifiers
and the values are character strings.
The shell interacts with the environment in several ways.
On invocation, the shell scans the environment
and creates a
parameter
for each name found,
giving it the corresponding value and marking it
.I export .
Executed commands inherit the environment.
If the user modifies the values of these
parameters
or creates new ones,
using the
.B export
or
.B typeset \-x
commands they become part of the
environment.
The environment seen by any executed command is thus composed
of any name-value pairs originally inherited by the shell,
whose values may be modified by the current shell,
plus any additions
which must be noted in
.B export