oracular (1) break.1posix.gz

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       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


       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 .

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