sh5.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

searched for
.IR arg .
The
.MS cd 1
command may not be executed by
.PN rsh5 .
.br
.ne 2.1v
.TP
\fBecho\fP [ \fIarg\fP... ]
.NXR "echo command (System V)"
Echo arguments. See
.MS echo 1sh5 
for usage and description.
.TP
\fBeval\fP [ \fIarg\fP... ]
.NXR "eval command (System V)"
The arguments are read as input
to the shell
and the resulting command(s) executed.
.TP
\fBexec\fP [ \fIarg\fP... ]
.NXR "exec command (System V)"
The command specified by
the arguments is executed in place of this shell
without creating a new process.
Input/output arguments may appear and, if no other
arguments are given, cause the shell
input/output to be modified.
.TP
\fBexit\fP [ \fIn\fP ] 
.NXR "exit command (System V)"
Causes a shell to exit
with the exit status specified by
.IR n .
If
.I n\^
is omitted the exit status is that of the last command executed
(an end-of-file will also cause the shell to exit.)
.TP
\fBexport\fP [ \fIname\fP... ]
.NXR "export command (System V)"
Each given
.I name 
is marked for automatic export to the environment
of subsequently-executed commands.
If no arguments are given, a list of all
names that are exported in this shell is printed.
Function names may 
.I not
be exported.
.TP
\fBhash\fP [ \fB\-r\fP ] [ \fIname\fP... ] 
.NXR "hash command (System V)"
For each 
.IR name\^ ,
the location in the search path of the command specified by 
.I name\^
is determined and remembered by the shell.
The 
.B \-r
option causes the shell to forget all remembered locations.
If no arguments are given, information about remembered commands is
presented.
\fIHits\fP is the number of times a command has been invoked by the shell process.
\fICost\fP is a measure of the work required to locate a
command in the search path.  There are certain situations 
which require that the stored location
of a command be recalculated.
Commands for which this will be done are indicated by an asterisk (\fB*\fR)
adjacent to the \fIhits\fR information.
\fICost\fR will be incremented when the recalculation is done.
.TP
\fBpwd\fP
.NXR "pwd command (System V)"
Print the current working directory.
For use and description, see 
.MS pwd 1 .
.TP
\fBread\fP [ \fIname\fP... ] 
.NXR "read command (System V)"
One line is read from the standard input and
the first
word is assigned to the first
.IR name ,
the second word
to the second
.IR name ,
etc., with leftover words assigned to the last
.IR name .
The return code is 0 unless an end-of-file is encountered.
.TP
\fBreadonly\fP [ \fIname\fP... ] 
.NXR "readonly command (System V)"
The given
.IR name s
are marked
.I readonly\^
and
the values of the these
.IR name s
may not be changed
by subsequent assignment.
If no arguments are given, a list
of all
.I readonly\^
names is printed.
.TP
\fBreturn\fP [ \fIn\fP ]
.NXR "return command (System V)"
Causes a function to exit with the return value specified by
.IR n .
If
.I n 
is omitted, the return status is that of the last command executed.
.TP
\fBset\fP [ \fB\-\-aefhkntuvx\fP [ \fIarg\fP... ] ] 
.NXR "set command (System V)"
.RS
.TP
.B \-a
Mark variables which are modified or created for export.
.TP
.B \-e
Exit immediately if a command
exits with a nonzero exit status.
.TP
.B \-f
Disable file name generation
.TP
.B \-h
Locate and remember function commands as functions are defined 
(function commands are normally located when the function is executed).
.TP
.B \-k
All keyword arguments are placed in the environment for a command,
not just those that precede the command name.
.TP
.B \-n
Read commands but do not execute them.
.TP
.B \-t
Exit after reading and executing one command.
.TP
.B \-u
Treat unset variables as an error when substituting.
.TP
.B \-v
Print shell input lines as they are read.
.TP
.B \-x
Print commands and their arguments as they are executed.
.TP
.B \-\-
Do not change any of the flags; useful in setting
.B $1
to
.BR \- .
.PP
Using
.B \+
rather than
.B \-
causes these flags to be turned off.
These flags can also be used upon invocation of the shell.
The current set of flags may be found in
.BR $\- .
The remaining arguments are positional
parameters and are assigned, in order, to
.BR $1 ,
.BR $2 ,
\&.\|.\|.\|.
If no arguments are given the values
of all names are printed.
.RE
.TP
\fBshift\fP [ \fIn\fP ] 
.NXR "shift command (System V)"
.br
The positional parameters from
.B $n+1
\&.\|.\|.
are renamed
.B $1
\&.\|.\|.\|.
If
.I n\^
is not given, it is assumed to be 1.
.TP
\fBtest\fP
.NXR "test command (System V)"
.br
Evaluate conditional expressions. 
For usage and description, see 
.MS test 1sh5 .
.TP
\fBtimes\fP
.NXR "times command (System V)"
.br
Print the accumulated user and system times for processes
run from the shell.
.TP
\fBtrap\fP [ \fIarg\fP ] [ \fIn\fP... ] 
.NXR "trap command (System V)"
The command
.I arg\^
is to be read and executed when the shell
receives signal(s)
.IR n .
Note that
.I arg\^
is scanned once when
the trap is set and once when the trap
is taken.
Trap commands are executed in order of signal number.
Any attempt to set a trap on a signal that
was ignored on entry to the current shell
is ineffective.
An attempt to trap on signal 11 (memory fault) produces an error.
If
.I arg\^
is absent all trap(s)
.I n\^
are reset
to their original values.
If
.I arg\^
is the null
string this signal is ignored by the shell and by the commands
it invokes.
If
.I n\^
is 0 the command
.I arg\^
is executed
on exit from the shell.
The
.B trap
command
with no arguments prints a list
of commands associated with each signal number.
.TP
\fBtype\fP [ \fIname\^\fP... ] 
.NXR "type command (System V)"
For each
.IR name ,
indicate how it would be interpreted if used as a command name.
.TP
\fBulimit\fP [ \fB\-fp\fP ] [ \fIn\fP ] 
.NXR "ulimit command (System V)"
imposes a size limit of
.I n\^
.RS
.TP
.B \-f
imposes a size limit of 
.I n
blocks on files written by child processes (files of any size may be read).
With no argument, the current limit is printed.
.TP
.B \-p
changes the pipe size to
.I n
(\s-1UNIX\s+1/\s-1RT\s+1 only).
.PP
If no option is given,
.B \-f
is assumed.
.RE
.TP
\fBumask\fP [ \fInnn\fP ] 
.NXR "umask command (System V)"
The user file-creation mask is set to
.I nnn\^.
For further information, see
.MS umask 2 .
If
.I nnn\^
is omitted, the current value of the mask is printed.
.TP
\fBunset\fP [ \fIname\fP... ] 
.NXR "unset command (System V)"
For each 
.IR name , 
remove the corresponding variable or function.
The variables 
\fB\s-1PATH\s+1\fP, \fB\s-1PS1\s+1\fP, \fB\s-1PS2\s+1\fP, \fB\s-1MAILCHECK\s+1\fP and \fB\s-1IFS\s+1\fP
cannot be unset.
.TP
\fBwait\fP [ \fIn\fP ] 
.NXR "wait command (System V)"
Wait for the specified process and report its termination status.
If
.I n\^
is not given all currently active child processes are waited for
and the return code is zero.
.PD
.PP
.SS Invocation
.NXR "sh5 command interpreter" "invoking"
If the shell is invoked through
.MS execve 2
and the first character of argument zero
is
.BR \- ,
commands are initially read from
.B /etc/profile
and from
.BR \s-1$HOME\s+1/.profile ,
if such files exist.
Thereafter, commands are read as described below, which
is also the case when the shell is invoked as
.BR /bin/sh5 .
The flags below are interpreted by the shell on invocation only. Note
that unless the 
.B \-c
or
.B \-s
flag is specified, the first argument is assumed to be the
name of a file containing commands, and the remaining
arguments are passed as positional parameters
to that command file:
.PP
.PD 0
.TP 10
.BI \-c "\| string\^"
If the
.B \-c
flag is present
commands are read from
.IR string .
.TP
.B \-s
If the
.B \-s
flag is present or if no
arguments remain
commands are read from the standard input.
Any remaining arguments specify the positional parameters.
Shell output (except for 
.IR "Special Commands\^" )
is written to file descriptor 2.
.TP
.B \-i
If the
.B \-i
flag is present or
if the shell input and output are attached to a terminal,
this shell is
.IR interactive .
In this case \s-1TERMINATE\s+1 is ignored (so that \fBkill 0\fP
does not kill an interactive shell) and \s-1INTERRUPT\s+1 is caught and ignored
(so that
.B wait
is interruptible).
In all cases, \s-1QUIT\s+1 is ignored by the shell.
.TP
.B \-r
If the
.B \-r
flag is present the shell is a restricted shell.
.PD
.PP
The remaining flags and arguments are described under the
.B set
command above.
.SS Rsh5 Only
.NXR "rsh5 program" "restricted"
The
.PN rsh5
shell is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
The actions of
.PN rsh5
are identical to those of
.PN sh5,
except that the following are disallowed:
.RS
.PD 0
.PP
changing directory, see
.MS cd 1,
.br
setting the value of
.SM
.BR $PATH\*S,
.br
specifying path or
command names containing
.BR / ,
.br
redirecting output
.RB ( >
and
.BR >> ).
.PD
.RE
.PP
The restrictions above are enforced
after \fB.profile\fP is interpreted.
.PP
When a command to be executed is found to be a shell procedure,
.PN rsh5
invokes
.PN sh5
to execute it.
Thus, it is possible to provide to the end-user shell procedures 
that have access to the full power of
the standard shell,
while imposing a limited menu of commands.
This scheme assumes that the end-user does not have write and
execute permissions in the same directory.
.PP
The net effect of these rules is that the writer of the
.B .profile
has complete control over user actions,
by performing guaranteed setup actions
and leaving the user in an appropriate directory
(probably
not
the login directory).
.PP
The system administrator often sets up a directory
of commands
(/usr/rbin )
that can be safely invoked by
.PN rsh5.
Some systems also provide a restricted editor,
.PN red ,
see
.MS ed 1.
.SH Exit Status
.NXR "sh5 command interpreter" "exit status"
Errors detected by the shell, such as syntax errors,
cause the shell
to return a nonzero exit status.
If the shell is being used noninteractively
execution of the shell file is abandoned.
Otherwise, the shell returns the exit status of
the last command executed (see also the
.B exit
command above).
.SH Restrictions
.NXR "sh5 command interpreter" "restricted"
If a command is executed, and a command with the same name is 
installed in a directory in the search path before the directory where the
original command was found, the shell will continue to 
.I exec\^
the original command.
Use the 
.B hash
command to correct this situation.
.PP
If you move the current directory or one above it, 
.B pwd\^
may not give the correct response.
Use the 
.PN cd\^
command with a full path name
to correct this situation.
.PP
If you startup a shell using 
.MS execve 2  
with an 'r' in the 
.I argv[0]
string, the System V shell goes into restricted mode.
.SH Files
/etc/profile
.br
\s-1$HOME\s+1/\fB.\fPprofile
.br
/tmp/sh\(**
.br
/dev/null
.SH See Also
cd(1), echo(1sh5),
login(1), printenv(1), pwd(1), sh(1), test(1sh5)
dup(2), execve(2), fork(2), pipe(2), 
ulimit(2), umask(2), wait(2), signal(3), a.out(5), environ(7) 
.NXE "sh5 command interpreter"