oasis-root

break.1p (5628B)

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.TH BREAK "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH 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.
.\"
.SH NAME
break
\(em exit from for, while, or until loop
.SH SYNOPSIS
.LP
.nf
break \fB[\fIn\fB]\fR
.fi
.SH DESCRIPTION
If
.IR n
is specified, the
.IR break
utility shall exit from the
.IR n th
enclosing
.BR for ,
.BR while ,
or
.BR until
loop. If
.IR n
is not specified,
.IR break
shall behave as if
.IR n
was specified as 1. Execution shall continue with the command
immediately following the exited loop. The value of
.IR n
is a positive decimal integer. If
.IR 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.
.P
A loop shall enclose a
.IR break
or
.IR continue
command if the loop lexically encloses the command. A loop lexically
encloses a
.IR break
or
.IR continue
command if the command is:
.IP " *" 4
Executing in the same execution environment (see
.IR "Section 2.12" ", " "Shell Execution Environment")
as the compound-list of the loop's do-group (see
.IR "Section 2.10.2" ", " "Shell Grammar Rules"),
and
.IP " *" 4
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
.BR while
or
.BR until
loop, in the compound-list following the
.BR while
or
.BR until
reserved word), and
.IP " *" 4
Not in the body of a function whose function definition command (see
.IR "Section 2.9.5" ", " "Function Definition Command")
is contained in a compound-list associated with the loop.
.P
If
.IR 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
.IR break
or
.IR continue
command, it is unspecified whether that loop encloses the command.
.SH OPTIONS
None.
.SH OPERANDS
See the DESCRIPTION.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
None.
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
Not used.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
.IP "\00" 6
Successful completion.
.IP >0 6
The
.IR n
value was not an unsigned decimal integer greater than or equal to 1.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH EXAMPLES
.LP
.nf
for i in *
do
    if test -d "$i"
    then break
    fi
done
.fi
.P
The results of running the following example are unspecified: there
are two loops in progress when the
.IR break
command is executed, and they are in the same execution environment,
but neither loop is lexically enclosing the
.IR break
command. (There are no loops lexically enclosing the
.IR continue
commands, either.)
.LP
.nf
foo() {
    for j in 1 2; do
        echo \(aqbreak 2\(aq >/tmp/do_break
        echo "  sourcing /tmp/do_break ($j)..."
        # the behavior of the break from running the following command
        # results in unspecified behavior:
        . /tmp/do_break
.P
        do_continue() { continue 2; }
        echo "  running do_continue ($j)..."
        # the behavior of the continue in the following function call
        # results in unspecified behavior (if execution reaches this
        # point):
        do_continue
.P
        trap \(aqcontinue 2\(aq 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
.fi
.SH "RATIONALE"
In early proposals, consideration was given to expanding the syntax of
.IR break
and
.IR continue
to refer to a label associated with the appropriate loop as a
preferable alternative to the
.IR n
method. However, this volume of POSIX.1\(hy2017 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:
.sp
.RS 4
.nf
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
.fi
.P
.RE
.P
and that this might be standardized after implementation experience is
achieved.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.14" ", " "Special Built-In Utilities"
.\"
.SH 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 .
.PP
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 .