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BREAK(1P) POSIX Programmer's Manual BREAK(1P)
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.
break — exit from for, while, or until loop
break [n]
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.
None.
See the DESCRIPTION.
Not used.
None.
None.
Default.
Not used.
The standard error shall be used only for diagnostic messages.
None.
None.
0 Successful completion.
>0 The n value was not an unsigned decimal integer greater
than or equal to 1.
Default.
The following sections are informative.
None.
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 ($i)..."
foo
done
In early proposals, consideration was given to expanding the
syntax of break and continue to refer to a label associated with
the appropriate loop as a preferable alternative to the n method.
However, this volume of POSIX.1‐2017 does reserve the name space
of command names ending with a <colon>. It is anticipated that a
future implementation could take advantage of this and provide
something like:
outofloop: for i in a b c d e
do
for j in 0 1 2 3 4 5 6 7 8 9
do
if test -r "${i}${j}"
then break outofloop
fi
done
done
and that this might be standardized after implementation
experience is achieved.
None.
Section 2.14, Special Built-In Utilities
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 .
IEEE/The Open Group 2017 BREAK(1P)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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