ksh.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

or
.B typeset \-x
commands.
.PP
The environment for any
.I simple-command
or function
may be augmented by prefixing it with one or more parameter assignments.
A parameter assignment argument is a word of the form
.IR identifier=value .
Thus:
.RS
.PP
\s-1TERM\s+1=450 \|cmd \|args				and
.br
(export \|\s-1TERM\s+1; \|\s-1TERM\s+1=450; \|cmd \|args)
.RE
.PP
are equivalent (as far as the above execution of
.I cmd
is concerned).
.PP
If the
.B \-k
flag is set,
.I all
parameter assignment arguments are placed in the environment,
even if they occur after the command name.
The following
first prints
.B "a=b c"
and then
.BR c:
.PP
.RS
.nf
echo \|a=b \|c
set \|\-k
echo \|a=b \|c
.fi
.RE
This feature is intended for use with scripts written
for early versions of the shell and its use in new scripts
is strongly discouraged.
It is likely to disappear someday.
.SS Functions.
.PP
The
.B function
reserved word, described in the
.I Commands
section above,
is used to define shell functions.
Shell functions are read in and stored internally.
Alias names are resolved when the function is read.
Functions are executed like commands with the arguments
passed as positional parameters.
(See
.I Execution
below).
.PP
Functions execute in the same process as the caller and
share all files
and present working directory with the
caller.
Traps caught by the caller are reset to their default action
inside the function.
A trap condition that is not caught or ignored by the
function causes the function to terminate and the condition
to be passed on to the caller.
A trap on
.SM
.B EXIT
set inside a function
is executed after the function completes in the environment
of the caller.
Ordinarily,
variables are shared between the calling program
and the function.
However,
the
.B typeset
special command used within a function
defines local variables whose scope includes
the current function and
all functions it calls.
.PP
The special command
.B return
is used to return
from function calls.
Errors within functions return control to the caller.
.PP
Function identifiers
can be listed with the
.B \-f
or
.B +f
option of the
.B typeset
special command.
The text of functions will also
be listed with
.BR \-f .
Function can be undefined with the
.B \-f
option of the
.B unset
special command.
.PP
Ordinarily,
functions are unset when the shell executes a shell script.
The
.B \-xf
option of the
.B typeset
command allows a function to be exported
to scripts that are executed without a separate
invocation of the shell.
Functions that need to be defined across separate
invocations of the shell should be specified in the
.SM
ENV
file with the 
.B \-xf
option of
.B typeset
.SS Jobs.
.PP
If the
.B monitor
option of the
.B set
command is turned on,
an interactive shell associates a \fIjob\fR with each pipeline.
It keeps
a table of current jobs, printed by the
.B jobs
command, and assigns them small integer numbers.
When a job is started asynchronously with
.BR & ,
the shell prints a line which looks
like:
.PP
.DT
	[1] 1234
.PP
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process id was 1234.
.PP
This paragraph and the next require features that are
not in all versions of the UNIX operating system and may not apply.
If you are running a job and wish to do something else you may hit the key
\fB^Z\fR (control-Z) which sends a STOP signal to the current job.
The shell will then normally indicate that the job has been `Stopped',
and print another prompt.
You can then manipulate the state of this job,
putting it in the background with the
.B bg
command, or run some other
commands and then eventually bring the job back into the foreground with
the foreground command
.BR fg .
A \fB^Z\fR takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.
.PP
A job being run in the background will stop if it tries to read
from the terminal.
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command ``stty tostop''.
If you set this
tty option, then background jobs will stop when they try to produce
output like they do when they try to read input.
.PP
There are several ways to refer to jobs in the shell.
A job can be referred to by the process id of any process of the job
or by one of the following:
.PD 0
.TP
.BI % number
The job with the given number.
.TP
.BI % string
Any job whose command line begins with
.IR string .
.TP
.BI %? string
Any job whose command line contains
.IR string .
.TP
.BI %%
Current job.
.TP
.BI %+
Equivalent to
.BR %% .
.TP
.BI %\-
Previous job.
.PD
.PP
This shell learns immediately whenever a process changes state.
It normally informs you whenever a job becomes blocked so that
no further progress is possible, but only just before it prints
a prompt.
This is done so that it does not otherwise disturb your work.
.PP
When the monitor mode is on, each background job that completes
triggers any trap set for
.BR CHLD .
.PP
When you try to leave the shell while jobs are running or stopped, you will
be warned that `You have stopped(running) jobs.'
You may use the
.B jobs
command to see what they are.
If you do this or immediately try to
exit again, the shell will not warn you a second time, and the stopped
jobs will be terminated.
.SS Signals.
The \s-1INT\s+1 and \s-1QUIT\s+1 signals for an invoked
command are ignored if the command is followed by
.B &
and job
.B monitor
option is not active.
Otherwise, signals have the values
inherited by the shell from its parent
(but see also
the
.B trap
command below).
.SS Execution.
Each time a command is executed, the above substitutions
are carried out.
If the command name matches one
of the
.I "Special Commands"
listed below,
it is executed within the
current shell process.
Next, the command name is checked to see if
it matches one of the user defined functions.
If it does,
the positional parameters are saved
and then reset to the arguments of the
.I function
call.
When the
.I function
completes or issues a
.BR return ,
the positional parameter list is restored
and any trap set on
.SM
.B EXIT
within the function is executed.
The value of a
.I function
is the value of the last command executed.
A function is also executed in the
current shell process.
If a command name is not a
.I "special command"
or a user defined
.IR function ,
a process is created and
an attempt is made to execute the command via
.IR exec (2).
.PP
The shell parameter
.SM PATH
defines the search path for
the directory containing the command.
Alternative directory names are separated by
a colon
.RB ( : ).
The default path is
.B /bin:/usr/bin:
(specifying
.BR /bin ,
.BR /usr/bin ,
and the current directory
in that order).
The current directory can be specified by
two or more adjacent colons, or by a colon
at the beginning or end of the path list.
If the command name contains a \fB/\fP then the search path
is not used.
Otherwise, each directory in the path is
searched for an executable file.
If the file has execute permission but is not a
directory or an
.B a.out
file,
it is assumed to be a file containing shell commands.
A sub-shell is spawned to read it.
All non-exported aliases,
functions,
and named parameters are removed in this case.
If the shell command
file doesn't have read permission,
or if the
.I setuid
and/or
.I setgid
bits are set on the file,
then the shell executes an agent whose job it is to
set up the permissions and execute the shell with the
shell command file passed down as an open file.
A parenthesized command is executed in
a sub-shell without removing non-exported quantities.
.SS Command Re-entry.
The text of the last
.SM
HISTSIZE
(default 128)
commands entered from a terminal device
is saved in a
.I history
file.
The file
.B \s-1$HOME\s+1/.sh_history
is used if the
.SM
HISTFILE
variable is not set
or is not writable.
A shell can access the commands of
all
.I interactive
shells which use the same named
.SM
.BR HISTFILE .
The special command
.B fc
is used to list or
edit a portion of this file.
The portion of the file to be edited or listed can be selected by
number or by giving the first character or
characters of the command.
A single command or range of commands can be specified.
If you do not specify an editor program as
an argument to
.B fc
then the value of the parameter
.SM
.B FCEDIT
is used.
If
.SM
.B FCEDIT
is not defined then
.B /bin/ed
is used.
The edited command(s) is printed and re-executed upon
leaving the editor.
The editor name
.B \-
is used to skip the editing phase and
to re-execute the command.
In this case a substitution parameter of the form
\fIold\fP\fB=\fP\fInew\fP
can be used to modify the command before execution.
For example, if
.B r
is aliased to
.B \(fmfc \-e \-\(fm
then typing
`\fBr bad=good c\fP'
will re-execute the most recent command which starts with the letter
.BR c ,
replacing the first occurrence of the string
.B bad
with the string
.BR good .
.SS In-line Editing Options
Normally, each command line entered from a terminal device is simply
typed followed by a new-line (`RETURN' or `LINE\ FEED').
If either the
.BR emacs ,
.BR gmacs ,
or
.B vi
option is active, the user can edit the command line.
To be in either of these edit modes
.B set
the corresponding
option.
An editing option is automatically selected each time the
.SM
.B VISUAL
or
.SM
.B EDITOR
variable is assigned a value ending in either of these
option names.
.PP
The editing features require that the user's terminal
accept `RETURN' as carriage return without line feed
and that a space (`\ ') must overwrite the current character on
the screen.
ADM terminal users should set the "space - advance"
switch to `space'.
Hewlett-Packard series 2621 terminal users should set the straps to
`bcGHxZ\ etX'.
.PP
The editing modes implement a concept where the user is looking through a
window at the current line.
The window width is the value of
.SM
.B COLUMNS
if it is defined, otherwise 80.
If the line is longer than the window width minus two, a mark is
displayed at the end of the window to notify the user.
As the cursor moves and reaches the window boundaries the window will be
centered about the cursor.
The mark is a
.BR > " (<" ,
.BR * )
if the line extends on the
right (left, both) side(s) of the window.
.PP
The search commands in each edit mode provide access to the history file.
Only strings are matched, not patterns, although a leading
.B ^
in the string restricts the match
to begin at the first character in the line.
.SS Emacs Editing Mode
This mode is entered by enabling either the
.I emacs
or
.I gmacs
option.
The only difference between these two modes is the way
they handle
.BR ^T .
To edit, the user
moves the cursor to the point needing correction and
then inserts or deletes characters or words as needed.
All the editing commands are control characters or escape
sequences.
The notation for control characters is caret (
.B ^
) followed
by the character.
For example,
.B ^F
is the notation for control
.BR F .
This is entered by depressing `f' while holding down the
`CTRL' (control) key.
The `SHIFT' key is
.I not
depressed.
(The notation
.B ^?
indicates the DEL (delete) key.)
.PP
The notation for escape sequences is
.B M-
followed by a
character.
For example,
.B M-f
(pronounced Meta f)
is entered by depressing ESC
(ascii
.BR 033 )
followed by `f'.
.RB ( M-F
would be the notation for ESC followed by `SHIFT' (capital) `F'.)
.PP
All edit commands
operate from any place on the line
(not just at the beginning).
Neither the "RETURN" nor the "LINE FEED" key is
entered after edit commands except when noted.
.PP
.PD 0
.TP 10
.BI ^F
Move cursor forward (right) one character.
.PP
.TP 10
.BI M-f
Move cursor forward one word.
(The emacs editor's idea of a word is a string of characters
consisting of only letters, digits and underscores.)
.PP
.TP 10
.BI ^B
Move cursor backward (left) one character.
.PP
.TP 10
.BI M-b
Move cursor backward one word.
.PP
.TP 10
.BI ^A
Move cursor to start of line.
.PP
.TP 10
.BI ^E
Move cursor to end of line.
.PP
.TP 10
.BI ^] char
Move cursor forward to character
.I char
on current line.
.PP
.TP 10
.BI M-^] char
Move cursor back to character
.I char
on current line.
.PP
.TP 10
.BI ^X^X
Interchange the cursor and mark.
.PP
.TP 10
.I erase
(User defined erase character as defined
by the
.IR stty (1)
command, usually
.B ^H
or
.BR # .)
Delete previous character.
.PP
.TP 10
.BI ^D
Delete current character.
.PP
.TP 10
.BI M-d
Delete current word.
.PP
.TP 10
.BI M-^H
(Meta-backspace) Delete previous word.
.PP
.TP 10
.BI M-h
Delete previous word.
.PP
.TP 10
.BI M-^?
(Meta-DEL) Delete previous word (if your interrupt character is
.B ^?
(DEL, the default) then this command will not work).
.PP
.TP 10
.BI ^T
Transpose current character with next character in
.I emacs
mode.
Transpose two previous characters in
.I gmacs
mode.
.PP
.TP 10
.BI ^C
Capitalize current character.
.PP
.TP 10
.BI M-c
Capitalize current word.
.PP
.TP 10
.BI M-l
Change the current word to lower case.
.PP
.TP 10
.BI ^K
Delete from the cursor to the end of the line.
If preceded by a numerical parameter whose value is less than the
current cursor position, then delete from given position
up to the cursor.
If preceded by a numerical parameter whose value is greater than the
current cursor position, then delete from cursor up to
given cursor position.
.PP
.TP 10
.BI ^W
Kill from the cursor to the mark.
.PP
.TP 10
.BI M-p
Push the region from the cursor to the mark on the stack.
.PP
.TP 10
.I kill
(User defined kill character as defined
by the stty command, usually
.B ^G
or
.BR @ .)
Kill the entire current line.
If two
.I kill
characters are entered in succession, all
kill characters from then on cause a line feed
(useful when using paper terminals).
.PP