BREAK(1)                   POSIX Programmer's Manual                  BREAK(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 .



IEEE/The Open Group                  2017                             BREAK(1)
