sh5.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)sh5.1	8.1	9/11/90
.TH sh5 1 
.SH Name
sh5, rsh5 \- shell, the standard/restricted command programming language
.SH Syntax
.B sh5
[\fB\-acefhiknrstuvx\fR] [\|\fIargs\fR\|]
.br
.B rsh5
[\fB\-acefhiknrstuvx\fR] [\|\fIargs\fR\|]
.SH Description
.NXB "sh5 command interpreter"
.NXR "rsh5 program"
The
.PN sh5
program is a command line interpreter and programming language
that executes commands read from a terminal
or a file.
The
.PN rsh5
program is a restricted version of the standard command interpreter
.PN sh5 . 
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\^
below
for the meaning of arguments to the shell.
This version of the shell is from System V Release 2.  For further
information about the standard Bourne shell interpreter, see 
.MS sh 1 .
.SS Definitions
.NXR "blank" "defined"
.NXR "parameter" "defined"
.NXR "name" "defined"
A blank is a tab or a space.  A name
is a sequence of letters, digits, or underscores beginning with a letter
or underscore.
A parameter
is a name, a digit, or any of the characters
.BR \(** ,
.BR @ ,
.BR # ,
.BR ? ,
.BR \- ,
.BR $ ,
and
.BR !\\^ .
.SS Commands
.NXR "simple command" "defined" 
A simple command is a sequence of nonblank
words separated by blanks.
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.
For further information, see
.MS execve 2 .
The value of a simple command is its exit status
if it terminates normally, or (octal) 200+\fIstatus\^\fP if
it terminates abnormally. For a list of status values, see
.MS signal 3 .
.PP
A pipeline is a sequence of one or more
commands separated by 
.BR |
(or, for historical compatibility, by
.BR ^ ). 
.NXR "pipeline" "defined"
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
.NXR "pipelines" "lists"
pipelines separated by
.BR ; ,
.BR & ,
.BR && ,
or
.BR || ,
and optionally terminated by
.B ;
or
.BR & .
Of these four symbols,
.B ;
and
.B &
have equal precedence,
which is lower than that of
.B &&
and
.BR || .
The symbols
.B &&
and
.B ||
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 &&
.RB (| |)
causes the
list following it to be executed only if the preceding
pipeline returns a zero (nonzero) exit status.
An arbitrary number of new-lines may appear in a
list, instead of semicolons, to delimit commands.
.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 \fIname\fP [ \fBin\fP \fIword...\fP ] \fBdo\fP \fIlist\fP \fBdone\fP
.NXR "for command (System V)"
Each time a
.B for
command is executed,
.I name\^
is set to the next
.I word\^
taken from the
.B in
.I word\^
list.
If
.BI in " word\^"
\&.\|.\|.
is omitted, then
the
.B for
command executes the \fBdo\fP \fIlist\^\fP
once for each positional parameter that is set.
For further information, see
.B Parameter Substitution
below.
Execution ends when there are no more words in the list.
.TP
\fBcase\fP \fIword\fP \fBin\fP  [ \fIpattern\fP [ | \fIpattern\fP ] ...) \fIlist\fP ;; ] ... \fBesac\fP
.NXR "case command (System V)"
.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 
except that a slash, a leading dot, or a dot immediately
following a slash need not be matched explicitly.
For further information, see
.B File Name Generation. 
.TP
\fBif\fP \fIlist\fP \fBthen\fP \fIlist\fP [ \fBelif\fP \fIlist\fP \fBthen\fP \fIlist\fP ] ...  [ \fBelse\fP \fIlist\fP ] \fBfi\fP
.NXR "if command (System V)"
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
\fBwhile\fP \fIlist\^\fP \fBdo\fP \fIlist\^\fP \fBdone\fP
.NXR "while command (SystemV)"
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.
The 
.B until
command may be used in place of
.B while
to negate
the loop termination test.
.TP
(\fIlist\^\fP)
Execute
.I list\^
in a sub-shell.
.TP
{\fIlist\^\fP;}
Simply executes
.I list\^
from current shell.
.TP
\fIname\^\fP () {\fIlist\^\fP\;}
Define a function
which is referenced by
.I name\^.
The body of the function
is the
.I list\^
of commands between
.BR { " and " } "."
Execution of functions is described below.  For further information, see
.B Execution.
.PD
.PP
The following 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 { }
.if t if  then  else  elif  f\&i  case  esac  for  while  until  do  done  {  }
.if t .RE
.SS Comments
.NXR "sh5 command interpreter" "comments"
A word beginning with
.B #
causes that word and all the following characters up to a new-line
to be ignored.
.SS Command Substitution
.NXR "sh5 command interpreter" "command substitution"
The standard output from a command enclosed in
a pair of grave accents 
.br
( \(ga\fIcommand\fP\(ga ) may be used as part 
or all of a word.
Trailing new-lines are removed.
.SS Parameter Substitution
.NXR "sh5 command interpreter" "parameter substitution"
The character
.B $
is used to introduce substitutable 
parameters.
There are two types of parameters,
positional and keyword.
If parameter is a digit, it is a positional parameter.
Positional parameters may be assigned values by
.BR set .
Keyword parameters (also known as variables)
may be assigned values by writing:
.EX
name = value [ name = value ] ...
.EE
.PP
Pattern-matching is not performed on value.
There cannot be a function and a variable with the same name.
.PP
.PD 0
.TP
\fB${\fP\fIparameter\^\fP\fB}\fP
The value, if any, of the parameter is substituted.
The braces are required only when
.I parameter\^
is followed by a letter, digit, or underscore
that is not to be interpreted as part of its name.
If
.I parameter\^
is
.B \(**
or
.BR @ ,
all the positional
parameters, starting with
.BR $1 ,
are substituted
(separated by spaces).
Parameter
.B $0
is set from argument zero when the shell
is invoked.
.TP
\fB${\fP\fIparameter\^\fP\fB:\-\fP\fIword\^\fP\fB}\fP
If
.I parameter\^
is set and is non-null, substitute its value.
Otherwise substitute
.IR word .
.TP
\fB${\fP\fIparameter\^\fP\fB:=\fP\fIword\^\fP\fB}\fP
If
.I parameter\^
is not set or is null
set it to
.IR word .
The value of the parameter is substituted.
Positional parameters may not be assigned to
in this way.
.TP
\fB${\fP\fIparameter\^\fP\fB:?\fP\fIword\^\fP\fB}\fP
If
.I parameter\^
is set and is non-null, substitute its value;
otherwise, print
.I word\^
and exit from the shell.
If
.I word\^
is omitted, the message
``parameter null or not set''
is printed.
.TP
\fB${\fP\fIparameter\^\fP\fB:+\fP\fIword\^\fP\fB}\fP
If
.I parameter\^
is set and is non-null, substitute
.IR word ;
otherwise substitute nothing.
.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,
.B pwd
is executed only if
.B d
is not set or is null:
.EX
echo ${d:\-`pwd`}
.EE
.PP
If the colon
.RB ( : )
is omitted from the above expressions, 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
.B #
The number of positional parameters in decimal.
.TP
.B \-
Flags supplied to the shell on invocation or by
the
.B set
command.
.TP
.B ?
The decimal value returned by the last synchronously executed command.
.TP
.B $
The process number of this shell.
.TP
.B !
The process number of the last background command invoked.
.PD
.RE
.PP
The following
parameters
are used by the shell:
.RS
.PD 0
.TP
.B
.SM LOGNAME
The name of the user's login account, corresponding to the login name
in the user database.
.TP
.B
.SM HOME
The default argument (home directory) for the
.MS cd 1
command.
.TP
.B
.SM PATH
The search path for commands.  For further information, see
.B Execution
below.
The user may not change
.B \s-1PATH\s+1
if executing under
.PN rsh5 .
.TP
.B
.SM CDPATH
The search path for the
.MS cd 1
command.
.TP
.B
.SM MAIL
If this parameter is set to the name of a mail file
and the 
.B \s-1MAILPATH\s+1
parameter is not set, the shell informs the user of the arrival of mail 
in the specified file.
.TP
.B
.SM MAILCHECK
This parameter specifies how often 
(in seconds) the shell
will check for the arrival of mail in the files specified by the
.B \s-1MAILPATH\s+1
or
.B \s-1MAIL\s+1
parameters.
The default value is 600 seconds (10 minutes).
If set to 0, the shell will check before each prompt.
.TP
.B
.SM MAILPATH
A colon 
.RB ( : )
separated list of file names.
If this parameter is set, the shell informs the user of the arrival of mail
in any of the specified files. 
Each file name can be followed by 
.B %
and a message that will be printed when the 
modification time changes.
The default message is
.B you have mail.
.TP
.SM
.B PS1
Primary prompt string, by default
.RB `` "$ \|" ''.
.TP
.SM
.B PS2
Secondary prompt string, by default
.RB `` "> \|" ''.
.TP
.SM
.B IFS