BREAK
Section: POSIX Programmer's Manual (1P)
Updated: 2017
Page Index
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
break
--- exit from for, while, or until loop
SYNOPSIS
break [n]
DESCRIPTION
If
n
is specified, the
break
utility shall exit from the
nth
enclosing
for,
while,
or
until
loop. If
n
is not specified,
break
shall behave as if
n
was specified as 1. Execution shall continue with the command
immediately following the exited loop. The value of
n
is a positive decimal integer. If
n
is greater than the number of enclosing loops, the outermost enclosing
loop shall be exited. If there is no enclosing loop, the behavior is
unspecified.
A loop shall enclose a
break
or
continue
command if the loop lexically encloses the command. A loop lexically
encloses a
break
or
continue
command if the command is:
- *
-
Executing in the same execution environment (see
Section 2.12, Shell Execution Environment)
as the compound-list of the loop's do-group (see
Section 2.10.2, Shell Grammar Rules),
and
- *
-
Contained in a compound-list associated with the loop (either in the
compound-list of the loop's do-group or, if the loop is a
while
or
until
loop, in the compound-list following the
while
or
until
reserved word), and
- *
-
Not in the body of a function whose function definition command (see
Section 2.9.5, Function Definition Command)
is contained in a compound-list associated with the loop.
If
n
is greater than the number of lexically enclosing loops and there is a
non-lexically enclosing loop in progress in the same execution
environment as the
break
or
continue
command, it is unspecified whether that loop encloses the command.
OPTIONS
None.
OPERANDS
See the DESCRIPTION.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
None.
ASYNCHRONOUS EVENTS
Default.
STDOUT
Not used.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
- 0
-
Successful completion.
- >0
-
The
n
value was not an unsigned decimal integer greater than or equal to 1.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
None.
EXAMPLES
for i in *
do
if test -d "$i"
then break
fi
done
The results of running the following example are unspecified: there
are two loops in progress when the
break
command is executed, and they are in the same execution environment,
but neither loop is lexically enclosing the
break
command. (There are no loops lexically enclosing the
continue
commands, either.)
foo() {
for j in 1 2; do
echo 'break 2' >/tmp/do_break
echo " sourcing /tmp/do_break ($j)..."
# the behavior of the break from running the following command
# results in unspecified behavior:
. /tmp/do_break
do_continue() { continue 2; }
echo " running do_continue ($j)..."
# the behavior of the continue in the following function call
# results in unspecified behavior (if execution reaches this
# point):
do_continue
trap 'continue 2' USR1
echo " sending SIGUSR1 to self ($j)..."
# the behavior of the continue in the trap invoked from the
# following signal results in unspecified behavior (if
# execution reaches this point):
kill -s USR1 $$
sleep 1
done
}
for i in 1 2; do
echo "running foo ($i)..."
foo
done
RATIONALE
In early proposals, consideration was given to expanding the syntax of
break
and
continue
to refer to a label associated with the appropriate loop as a
preferable alternative to the
n
method. However, this volume of POSIX.1-2017 does reserve the name space of command names
ending with a
<colon>.
It is anticipated that a future implementation could take advantage of
this and provide something like:
-
outofloop: for i in a b c d e
do
for j in 0 1 2 3 4 5 6 7 8 9
do
if test -r "${i}${j}"
then break outofloop
fi
done
done
and that this might be standardized after implementation experience is
achieved.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.14,
Special Built-In Utilities
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .