DragonFly On-Line Manual Pages
BUILTIN(1) DragonFly General Commands Manual BUILTIN(1)
NAME
builtin, !, %, ., :, @, [, {, }, alias, alloc, bg, bind, bindkey, break,
breaksw, builtins, case, cd, chdir, command, complete, continue, default,
dirs, do, done, echo, echotc, elif, else, end, endif, endsw, esac, eval,
exec, exit, export, false, fc, fg, filetest, fi, for, foreach, getopts,
glob, goto, hash, hashstat, history, hup, if, jobid, jobs, kill, let,
limit, local, log, login, logout, ls-F, nice, nohup, notify, onintr,
popd, printenv, printf, pushd, pwd, read, readonly, rehash, repeat,
return, sched, set, setenv, settc, setty, setvar, shift, source, stop,
suspend, switch, telltc, termname, test, then, time, times, trap, true,
type, ulimit, umask, unalias, uncomplete, unhash, unlimit, unset,
unsetenv, until, wait, where, which, while, wordexp, wordexp2 - shell
built-in commands
SYNOPSIS
See the built-in command description in the appropriate shell manual
page.
DESCRIPTION
Shell builtin commands are commands that can be executed within the
running shell's process. Note that, in the case of csh(1) builtin
commands, the command is executed in a subshell if it occurs as any
component of a pipeline except the last.
If a command specified to the shell contains a slash `/', the shell will
not execute a builtin command, even if the last component of the
specified command matches the name of a builtin command. Thus, while
specifying "echo" causes a builtin command to be executed under shells
that support the echo builtin command, specifying "/bin/echo" or "./echo"
does not.
While some builtin commands may exist in more than one shell, their
operation may be different under each shell which supports them. Below
is a table which lists shell builtin commands, the standard shells that
support them and whether they exist as standalone utilities.
Only builtin commands for the csh(1) and sh(1) shells are listed here.
Consult a shell's manual page for details on the operation its builtin
commands. Beware that the sh(1) manual page, at least, calls some of
these commands "built-in commands" and some of them "reserved words".
Users of other shells may need to consult an info(1) page or other
sources of documentation.
Commands marked "No**" under External do exist externally, but are
implemented as scripts using a builtin command of the same name.
Command External csh(1) sh(1)
! No No Yes
% No Yes No
. No No Yes
: No Yes Yes
@ No Yes No
[ Yes No Yes
{ No No Yes
} No No Yes
alias No** Yes Yes
alloc No Yes No
bg No** Yes Yes
bind No No Yes
bindkey No Yes No
break No Yes Yes
breaksw No Yes No
builtin No No Yes
builtins No Yes No
case No Yes Yes
cd No** Yes Yes
chdir No Yes Yes
command No** No Yes
complete No Yes No
continue No Yes Yes
default No Yes No
dirs No Yes No
do No No Yes
done No No Yes
echo Yes Yes Yes
echotc No Yes No
elif No No Yes
else No Yes Yes
end No Yes No
endif No Yes No
endsw No Yes No
esac No No Yes
eval No Yes Yes
exec No Yes Yes
exit No Yes Yes
export No No Yes
false Yes No Yes
fc No** No Yes
fg No** Yes Yes
filetest No Yes No
fi No No Yes
for No No Yes
foreach No Yes No
getopts No** No Yes
glob No Yes No
goto No Yes No
hash No No Yes
hashstat No Yes No
history No Yes No
hup No Yes No
if No Yes Yes
jobid No No Yes
jobs No** Yes Yes
kill Yes Yes Yes
let No No Yes
limit No Yes No
local No No Yes
log No Yes No
login Yes Yes No
logout No Yes No
ls-F No Yes No
nice Yes Yes No
nohup Yes Yes No
notify No Yes No
onintr No Yes No
popd No Yes No
printenv Yes Yes No
printf Yes No Yes
pushd No Yes No
pwd Yes No Yes
read No** No Yes
readonly No No Yes
rehash No Yes No
repeat No Yes No
return No No Yes
sched No Yes No
set No Yes Yes
setenv No Yes No
settc No Yes No
setty No Yes No
setvar No No Yes
shift No Yes Yes
source No Yes No
stop No Yes No
suspend No Yes No
switch No Yes No
telltc No Yes No
termname No Yes No
test Yes No Yes
then No No Yes
time Yes Yes No
times No No Yes
trap No No Yes
true Yes No Yes
type No No Yes
ulimit No No Yes
umask No** Yes Yes
unalias No** Yes Yes
uncomplete No Yes No
unhash No Yes No
unlimit No Yes No
unset No Yes Yes
unsetenv No Yes No
until No No Yes
wait No** Yes Yes
where No Yes No
which Yes Yes No
while No Yes Yes
wordexp No No Yes
wordexp2 No No Yes
Note that the wordexp and wordexp2 commands are only meant to be used by
wordexp(3) and not by the user.
SEE ALSO
csh(1), echo(1), false(1), info(1), kill(1), login(1), nice(1), nohup(1),
printenv(1), printf(1), pwd(1), sh(1), test(1), time(1), true(1),
which(1), wordexp(3)
HISTORY
The builtin manual page first appeared in FreeBSD 3.4.
AUTHORS
This manual page was written by Sheldon Hearn <sheldonh@FreeBSD.org>.
DragonFly 5.9-DEVELOPMENT October 9, 2020 DragonFly 5.9-DEVELOPMENT
return(n) Tcl Built-In Commands return(n)
______________________________________________________________________________
NAME
return - Return from a procedure, or set return code of a script
SYNOPSIS
return ?result?
return ?-code code? ?result?
return ?option value ...? ?result?
______________________________________________________________________________
DESCRIPTION
In its simplest usage, the return command is used without options in
the body of a procedure to immediately return control to the caller of
the procedure. If a result argument is provided, its value becomes the
result of the procedure passed back to the caller. If result is not
specified then an empty string will be returned to the caller as the
result of the procedure.
The return command serves a similar function within script files that
are evaluated by the source command. When source evaluates the
contents of a file as a script, an invocation of the return command
will cause script evaluation to immediately cease, and the value result
(or an empty string) will be returned as the result of the source
command.
EXCEPTIONAL RETURN CODES
In addition to the result of a procedure, the return code of a
procedure may also be set by return through use of the -code option.
In the usual case where the -code option is not specified the procedure
will return normally. However, the -code option may be used to
generate an exceptional return from the procedure. Code may have any
of the following values:
ok (or 0) Normal return: same as if the option is omitted. The
return code of the procedure is 0 (TCL_OK).
error (or 1) Error return: the return code of the procedure is 1
(TCL_ERROR). The procedure command behaves in its calling
context as if it were the command error result. See below
for additional options.
return (or 2)
The return code of the procedure is 2 (TCL_RETURN). The
procedure command behaves in its calling context as if it
were the command return (with no arguments).
break (or 3) The return code of the procedure is 3 (TCL_BREAK). The
procedure command behaves in its calling context as if it
were the command break.
continue (or 4)
The return code of the procedure is 4 (TCL_CONTINUE). The
procedure command behaves in its calling context as if it
were the command continue.
value Value must be an integer; it will be returned as the
return code for the current procedure.
When a procedure wants to signal that it has received invalid arguments
from its caller, it may use return -code error with result set to a
suitable error message. Otherwise usage of the return -code option is
mostly limited to procedures that implement a new control structure.
The return -code command acts similarly within script files that are
evaluated by the source command. During the evaluation of the contents
of a file as a script by source, an invocation of the return -code code
command will cause the return code of source to be code.
RETURN OPTIONS
In addition to a result and a return code, evaluation of a command in
Tcl also produces a dictionary of return options. In general usage,
all option value pairs given as arguments to return become entries in
the return options dictionary, and any values at all are acceptable
except as noted below. The catch command may be used to capture all of
this information -- the return code, the result, and the return options
dictionary -- that arise from evaluation of a script.
As documented above, the -code entry in the return options dictionary
receives special treatment by Tcl. There are other return options also
recognized and treated specially by Tcl. They are:
-errorcode list
The -errorcode option receives special treatment only when the
value of the -code option is TCL_ERROR. Then the list value is
meant to be additional information about the error, presented as
a Tcl list for further processing by programs. If no -errorcode
option is provided to return when the -code error option is
provided, Tcl will set the value of the -errorcode entry in the
return options dictionary to the default value of NONE. The
-errorcode return option will also be stored in the global
variable errorCode.
-errorinfo info
The -errorinfo option receives special treatment only when the
value of the -code option is TCL_ERROR. Then info is the
initial stack trace, meant to provide to a human reader
additional information about the context in which the error
occurred. The stack trace will also be stored in the global
variable errorInfo. If no -errorinfo option is provided to
return when the -code error option is provided, Tcl will provide
its own initial stack trace value in the entry for -errorinfo.
Tcl's initial stack trace will include only the call to the
procedure, and stack unwinding will append information about
higher stack levels, but there will be no information about the
context of the error within the procedure. Typically the info
value is supplied from the value of -errorinfo in a return
options dictionary captured by the catch command (or from the
copy of that information stored in the global variable
errorInfo).
-errorstack list
The -errorstack option receives special treatment only when the |
value of the -code option is TCL_ERROR. Then list is the |
initial error stack, recording actual argument values passed to |
each proc level. The error stack will also be reachable through |
info errorstack. If no -errorstack option is provided to return |
when the -code error option is provided, Tcl will provide its |
own initial error stack in the entry for -errorstack. Tcl's |
initial error stack will include only the call to the procedure, |
and stack unwinding will append information about higher stack |
levels, but there will be no information about the context of |
the error within the procedure. Typically the list value is |
supplied from the value of -errorstack in a return options |
dictionary captured by the catch command (or from the copy of |
that information from info errorstack).
-level level
The -level and -code options work together to set the return
code to be returned by one of the commands currently being
evaluated. The level value must be a non-negative integer
representing a number of levels on the call stack. It defines
the number of levels up the stack at which the return code of a
command currently being evaluated should be code. If no -level
option is provided, the default value of level is 1, so that
return sets the return code that the current procedure returns
to its caller, 1 level up the call stack. The mechanism by
which these options work is described in more detail below.
-options options
The value options must be a valid dictionary. The entries of
that dictionary are treated as additional option value pairs for
the return command.
RETURN CODE HANDLING MECHANISMS
Return codes are used in Tcl to control program flow. A Tcl script is
a sequence of Tcl commands. So long as each command evaluation returns
a return code of TCL_OK, evaluation will continue to the next command
in the script. Any exceptional return code (non-TCL_OK) returned by a
command evaluation causes the flow on to the next command to be
interrupted. Script evaluation ceases, and the exceptional return code
from the command becomes the return code of the full script evaluation.
This is the mechanism by which errors during script evaluation cause an
interruption and unwinding of the call stack. It is also the mechanism
by which commands like break, continue, and return cause script
evaluation to terminate without evaluating all commands in sequence.
Some of Tcl's built-in commands evaluate scripts as part of their
functioning. These commands can make use of exceptional return codes
to enable special features. For example, the built-in Tcl commands
that provide loops -- such as while, for, and foreach -- evaluate a
script that is the body of the loop. If evaluation of the loop body
returns the return code of TCL_BREAK or TCL_CONTINUE, the loop command
can react in such a way as to give the break and continue commands
their documented interpretation in loops.
Procedure invocation also involves evaluation of a script, the body of
the procedure. Procedure invocation provides special treatment when
evaluation of the procedure body returns the return code TCL_RETURN.
In that circumstance, the -level entry in the return options dictionary
is decremented. If after decrementing, the value of the -level entry
is 0, then the value of the -code entry becomes the return code of the
procedure. If after decrementing, the value of the -level entry is
greater than zero, then the return code of the procedure is TCL_RETURN.
If the procedure invocation occurred during the evaluation of the body
of another procedure, the process will repeat itself up the call stack,
decrementing the value of the -level entry at each level, so that the
code will be the return code of the current command level levels up the
call stack. The source command performs the same handling of the
TCL_RETURN return code, which explains the similarity of return
invocation during a source to return invocation within a procedure.
The return code of the return command itself triggers this special
handling by procedure invocation. If return is provided the option
-level 0, then the return code of the return command itself will be the
value code of the -code option (or TCL_OK by default). Any other value
for the -level option (including the default value of 1) will cause the
return code of the return command itself to be TCL_RETURN, triggering a
return from the enclosing procedure.
EXAMPLES
First, a simple example of using return to return from a procedure,
interrupting the procedure body.
proc printOneLine {} {
puts "line 1" ;# This line will be printed.
return
puts "line 2" ;# This line will not be printed.
}
Next, an example of using return to set the value returned by the
procedure.
proc returnX {} {return X}
puts [returnX] ;# prints "X"
Next, a more complete example, using return -code error to report
invalid arguments.
proc factorial {n} {
if {![string is integer $n] || ($n < 0)} {
return -code error \
"expected non-negative integer,\
but got \"$n\""
}
if {$n < 2} {
return 1
}
set m [expr {$n - 1}]
set code [catch {factorial $m} factor]
if {$code != 0} {
return -code $code $factor
}
set product [expr {$n * $factor}]
if {$product < 0} {
return -code error \
"overflow computing factorial of $n"
}
return $product
}
Next, a procedure replacement for break.
proc myBreak {} {
return -code break
}
With the -level 0 option, return itself can serve as a replacement for
break, with the help of interp alias.
interp alias {} Break {} return -level 0 -code break
An example of using catch and return -options to re-raise a caught
error:
proc doSomething {} {
set resource [allocate]
catch {
# Long script of operations
# that might raise an error
} result options
deallocate $resource
return -options $options $result
}
Finally an example of advanced use of the return options to create a
procedure replacement for return itself:
proc myReturn {args} {
set result ""
if {[llength $args] % 2} {
set result [lindex $args end]
set args [lrange $args 0 end-1]
}
set options [dict merge {-level 1} $args]
dict incr options -level
return -options $options $result
}
SEE ALSO
break(n), catch(n), continue(n), dict(n), error(n), errorCode(n),
errorInfo(n), proc(n), source(n), throw(n), try(n)
KEYWORDS
break, catch, continue, error, exception, procedure, result, return
Tcl 8.5 return(n)