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| <CENTER><H2>Proper handling of SIGINT/SIGQUIT</H2></CENTER> |
| <img src=linie.png width="100%" alt=" "> |
| <P> |
| |
| <table border=1 cellpadding=4> |
| <tr><th valign=top align=left>Abstract: </th> |
| <td valign=top align=left> |
| In UNIX terminal sessions, you usually have a key like |
| <code>C-c</code> (Control-C) to immediately end whatever program you |
| have running in the foreground. This should work even when the program |
| you called has called other programs in turn. Everything should be |
| aborted, giving you your command prompt back, no matter how deep the |
| call stack is. |
| |
| <p>Basically, it's trivial. But the existence of interactive |
| applications that use SIGINT and/or SIGQUIT for other purposes than a |
| complete immediate abort make matters complicated, and - as was to |
| expect - left us with several ways to solve the problems. Of course, |
| existing shells and applications follow different ways. |
| |
| <P>This Web pages outlines different ways to solve the problem and |
| argues that only one of them can do everything right, although it |
| means that we have to fix some existing software. |
| |
| |
| |
| </td></tr><tr><th valign=top align=left>Intended audience: </th> |
| <td valign=top align=left>Programmers who implement programs that catch SIGINT/SIGQUIT. |
| <BR>Programmers who implements shells or shell-like programs that |
| execute batches of programs. |
| |
| <p>Users who have problems problems getting rid of runaway shell |
| scripts using <code>Control-C</code>. Or have interactive applications |
| that don't behave right when sending SIGINT. Examples are emacs'es |
| that die on Control-g or shellscript statements that sometimes are |
| executed and sometimes not, apparently not determined by the user's |
| intention. |
| |
| |
| </td></tr><tr><th valign=top align=left>Required knowledge: </th> |
| <td valign=top align=left>You have to know what it means to catch SIGINT or SIGQUIT and how |
| processes are waiting for other processes (children) they spawned. |
| |
| |
| </td></tr></table> |
| <img src=linie.png width="100%" alt=" "> |
| |
| |
| <H3>Basic concepts</H3> |
| |
| What technically happens when you press Control-C is that all programs |
| running in the foreground in your current terminal (or virtual |
| terminal) get the signal SIGINT sent. |
| |
| <p>You may change the key that triggers the signal using |
| <code>stty</code> and running programs may remap the SIGINT-sending |
| key at any time they like, without your intervention and without |
| asking you first. |
| |
| <p>The usual reaction of a running program to SIGINT is to exit. |
| However, not all program do an exit on SIGINT, programs are free to |
| use the signal for other actions or to ignore it at all. |
| |
| <p>All programs running in the foreground receive the signal. This may |
| be a nested "stack" of programs: You started a program that started |
| another and the outer is waiting for the inner to exit. This nesting |
| may be arbitrarily deep. |
| |
| <p>The innermost program is the one that decides what to do on SIGINT. |
| It may exit, do something else or do nothing. Still, when the user hit |
| SIGINT, all the outer programs are awaken, get the signal and may |
| react on it. |
| |
| <H3>What we try to achieve</H3> |
| |
| The problem is with shell scripts (or similar programs that call |
| several subprograms one after another). |
| |
| <p>Let us consider the most basic script: |
| <PRE> |
| #! /bin/sh |
| program1 |
| program2 |
| </PRE> |
| and the usual run looks like this: |
| <PRE> |
| $ sh myscript |
| [output of program1] |
| [output of program2] |
| $ |
| </PRE> |
| |
| <p>Let us assume that both programs do nothing special on SIGINT, they |
| just exit. |
| |
| <p>Now imagine the user hits C-c while a shellscript is executing its |
| first program. The following programs receive SIGINT: program1 and |
| also the shell executing the script. program1 exits. |
| |
| <p>But what should the shell do? If we say that it is only the |
| innermost's programs business to react on SIGINT, the shell will do |
| nothing special (not exit) and it will continue the execution of the |
| script and run program2. But this is wrong: The user's intention in |
| hitting C-c is to abort the whole script, to get his prompt back. If |
| he hits C-c while the first program is running, he does not want |
| program2 to be even started. |
| |
| <p>here is what would happen if the shell doesn't do anything: |
| <PRE> |
| $ sh myscript |
| [first half of program1's output] |
| C-c [users presses C-c] |
| [second half of program1's output will not be displayed] |
| [output of program2 will appear] |
| </PRE> |
| |
| |
| <p>Consider a more annoying example: |
| <pre> |
| #! /bin/sh |
| # let's assume there are 300 *.dat files |
| for file in *.dat ; do |
| dat2ascii $dat |
| done |
| </pre> |
| |
| If your shell wouldn't end if the user hits <code>C-c</code>, |
| <code>C-c</code> would just end <strong>one</strong> dat2ascii run and |
| the script would continue. Thus, you had to hit <code>C-c</code> up to |
| 300 times to end this script. |
| |
| <H3>Alternatives to do so</H3> |
| |
| <p>There are several ways to handle abortion of shell scripts when |
| SIGINT is received while a foreground child runs: |
| |
| <menu> |
| |
| <li>As just outlined, the shellscript may just continue, ignoring the |
| fact that the user hit <code>C-c</code>. That way, your shellscript - |
| including any loops - would continue and you had no chance of aborting |
| it except using the kill command after finding out the outermost |
| shell's PID. This "solution" will not be discussed further, as it is |
| obviously not desirable. |
| |
| <p><li>The shell itself exits immediately when it receives SIGINT. Not |
| only the program called will exit, but the calling (the |
| script-executing) shell. The first variant is to exit the shell (and |
| therefore discontinuing execution of the script) immediately, while |
| the background program may still be executing (remember that although |
| the shell is just waiting for the called program to exit, it is woken |
| up and may act). I will call the way of doing things the "IUE" (for |
| "immediate unconditional exit") for the rest of this document. |
| |
| <p><li>As a variant of the former, when the shell receives SIGINT |
| while it is waiting for a child to exit, the shell does not exit |
| immediately. but it remembers the fact that a SIGINT happened. After |
| the called program exits and the shell's wait ends, the shell will |
| exit itself and hence discontinue the script. I will call the way of |
| doing things the "WUE" (for "wait and unconditional exit") for the |
| rest of this document. |
| |
| <p><li>There is also a way that the calling shell can tell whether the |
| called program exited on SIGINT and if it ignored SIGINT (or used it |
| for other purposes). As in the <sl>WUE</sl> way, the shell waits for |
| the child to complete. It figures whether the program was ended on |
| SIGINT and if so, it discontinue the script. If the program did any |
| other exit, the script will be continued. I will call the way of doing |
| things the "WCE" (for "wait and cooperative exit") for the rest of |
| this document. |
| |
| </menu> |
| |
| <H3>The problem</H3> |
| |
| On first sight, all three solutions (IUE, WUE and WCE) all seem to do |
| what we want: If C-c is hit while the first program of the shell |
| script runs, the script is discontinued. The user gets his prompt back |
| immediately. So what are the difference between these way of handling |
| SIGINT? |
| |
| <p>There are programs that use the signal SIGINT for other purposes |
| than exiting. They use it as a normal keystroke. The user is expected |
| to use the key that sends SIGINT during a perfectly normal program |
| run. As a result, the user sends SIGINT in situations where he/she |
| does not want the program or the script to end. |
| |
| <p>The primary example is the emacs editor: C-g does what ESC does in |
| other applications: It cancels a partially executed or prepared |
| operation. Technically, emacs remaps the key that sends SIGINT from |
| C-c to C-g and catches SIGINT. |
| |
| <p>Remember that the SIGINT is sent to all programs running in the |
| foreground. If emacs is executing from a shell script, both emacs and |
| the shell get SIGINT. emacs is the program that decides what to do: |
| Exit on SIGINT or not. emacs decides not to exit. The problem arises |
| when the shell draws its own conclusions from receiving SIGINT without |
| consulting emacs for its opinion. |
| |
| <p>Consider this script: |
| <PRE> |
| #! /bin/sh |
| emacs /tmp/foo |
| cp /tmp/foo /home/user/mail/sent |
| </PRE> |
| |
| <p>If C-g is used in emacs, both the shell and emacs will received |
| SIGINT. Emacs will not exit, the user used C-g as a normal editing |
| keystroke, he/she does not want the script to be aborted on C-g. |
| |
| <p>The central problem is that the second command (cp) may |
| unintentionally be killed when the shell draws its own conclusion |
| about the user's intention. The innermost program is the only one to |
| judge. |
| |
| <H3>One more example</H3> |
| |
| <p>Imagine a mail session using a curses mailer in a tty. You called |
| your mailer and started to compose a message. Your mailer calls emacs. |
| <code>C-g</code> is a normal editing key in emacs. Technically it |
| sends SIGINT (it was <code>C-c</code>, but emacs remapped the key) to |
| <menu> |
| <li>emacs |
| <li>the shell between your mailer and emacs, the one from your mailers |
| system("emacs /tmp/bla.44") command |
| <li>the mailer itself |
| <li>possibly another shell if your mailer was called by a shell script |
| or from another application using system(3) |
| <li>your interactive shell (which ignores it since it is interactive |
| and hence is not relevant to this discussion) |
| </menu> |
| |
| <p>If everyone just exits on SIGINT, you will be left with nothing but |
| your login shell, without asking. |
| |
| <p>But for sure you don't want to be dropped out of your editor and |
| out of your mailer back to the commandline, having your edited data |
| and mailer status deleted. |
| |
| <p>Understand the difference: While <code>C-g</code> is used an a kind |
| of abort key in emacs, it isn't the major "abort everything" key. When |
| you use <code>C-g</code> in emacs, you want to end some internal emacs |
| command. You don't want your whole emacs and mailer session to end. |
| |
| <p>So, if the shell exits immediately if the user sends SIGINT (the |
| second of the four ways shown above), the parent of emacs would die, |
| leaving emacs without the controlling tty. The user will lose it's |
| editing session immediately and unrecoverable. If the "main" shell of |
| the operating system defaults to this behavior, every editor session |
| that is spawned from a mailer or such will break (because it is |
| usually executed by system(3), which calls /bin/sh). This was the case |
| in FreeBSD before I and Bruce Evans changed it in 1998. |
| |
| <p>If the shell recognized that SIGINT was sent and exits after the |
| current foreground process exited (the third way of the four), the |
| editor session will not be disturbed, but things will still not work |
| right. |
| |
| <H3>A further look at the alternatives</H3> |
| |
| <p>Still considering this script to examine the shell's actions in the |
| IUE, WUE and ICE way of handling SIGINT: |
| <PRE> |
| #! /bin/sh |
| emacs /tmp/foo |
| cp /tmp/foo /home/user/mail/sent |
| </PRE> |
| |
| <p>The IUE ("immediate unconditional exit") way does not work at all: |
| emacs wants to survive the SIGINT (it's a normal editing key for |
| emacs), but its parent shell unconditionally thinks "We received |
| SIGINT. Abort everything. Now.". The shell will exit even before emacs |
| exits. But this will leave emacs in an unusable state, since the death |
| of its calling shell will leave it without required resources (file |
| descriptors). This way does not work at all for shellscripts that call |
| programs that use SIGINT for other purposes than immediate exit. Even |
| for programs that exit on SIGINT, but want to do some cleanup between |
| the signal and the exit, may fail before they complete their cleanup. |
| |
| <p>It should be noted that this way has one advantage: If a child |
| blocks SIGINT and does not exit at all, this way will get control back |
| to the user's terminal. Since such programs should be banned from your |
| system anyway, I don't think that weighs against the disadvantages. |
| |
| <p>WUE ("wait and unconditional exit") is a little more clever: If C-g |
| was used in emacs, the shell will get SIGINT. It will not immediately |
| exit, but remember the fact that a SIGINT happened. When emacs ends |
| (maybe a long time after the SIGINT), it will say "Ok, a SIGINT |
| happened sometime while the child was executing, the user wants the |
| script to be discontinued". It will then exit. The cp will not be |
| executed. But that's bad. The "cp" will be executed when the emacs |
| session ended without the C-g key ever used, but it will not be |
| executed when the user used C-g at least one time. That is clearly not |
| desired. Since C-g is a normal editing key in emacs, the user expects |
| the rest of the script to behave identically no matter what keys he |
| used. |
| |
| <p>As a result, the "WUE" way is better than the "IUE" way in that it |
| does not break SIGINT-using programs completely. The emacs session |
| will end undisturbed. But it still does not support scripts where |
| other actions should be performed after a program that use SIGINT for |
| non-exit purposes. Since the behavior is basically undeterminable for |
| the user, this can lead to nasty surprises. |
| |
| <p>The "WCE" way fixes this by "asking" the called program whether it |
| exited on SIGINT or not. While emacs receives SIGINT, it does not exit |
| on it and a calling shell waiting for its exit will not be told that |
| it exited on SIGINT. (Although it receives SIGINT at some point in |
| time, the system does not enforce that emacs will exit with |
| "I-exited-on-SIGINT" status. This is under emacs' control, see below). |
| |
| <p>this still work for the normal script without SIGINT-using |
| programs:</p> |
| <PRE> |
| #! /bin/sh |
| program1 |
| program2 |
| </PRE> |
| |
| Unless program1 and program2 mess around with signal handling, the |
| system will tell the calling shell whether the programs exited |
| normally or as a result of SIGINT. |
| |
| <p>The "WCE" way then has an easy way to things right: When one called |
| program exited with "I-exited-on-SIGINT" status, it will discontinue |
| the script after this program. If the program ends without this |
| status, the next command in the script is started. |
| |
| <p>It is important to understand that a shell in "WCE" modus does not |
| need to listen to the SIGINT signal at all. Both in the |
| "emacs-then-cp" script and in the "several-normal-programs" script, it |
| will be woken up and receive SIGINT when the user hits the |
| corresponding key. But the shell does not need to react on this event |
| and it doesn't need to remember the event of any SIGINT, either. |
| Telling whether the user wants to end a script is done by asking that |
| program that has to decide, that program that interprets keystrokes |
| from the user, the innermost program. |
| |
| <H3>So everything is well with WCE?</H3> |
| |
| Well, almost. |
| |
| <p>The problem with the "WCE" modus is that there are broken programs |
| that do not properly communicate the required information up to the |
| calling program. |
| |
| <p>Unless a program messes with signal handling, the system does this |
| automatically. |
| |
| <p>There are programs that want to exit on SIGINT, but they don't let |
| the system do the automatic exit, because they want to do some |
| cleanup. To do so, they catch SIGINT, do the cleanup and then exit by |
| themselves. |
| |
| <p>And here is where the problem arises: Once they catch the signal, |
| the system will no longer communicate the "I-exited-on-SIGINT" status |
| to the calling program automatically. Even if the program exit |
| immediately in the signal handler of SIGINT. Once it catches the |
| signal, it has to take care of communicating the signal status |
| itself. |
| |
| <p>Some programs don't do this. On SIGINT, they do cleanup and exit |
| immediately, but the calling shell isn't told about the non-normal exit |
| and it will call the next program in the script. |
| |
| <p>As a result, the user hits SIGINT and while one program exits, the |
| shellscript continues. To him/her it looks like the shell fails to |
| obey to his abortion command. |
| |
| <p>Both IUE or WUE shell would not have this problem, since they |
| discontinue the script on their own. But as I said, they don't support |
| programs using SIGINT for non-exiting purposes, no matter whether |
| these programs properly communicate their signal status to the calling |
| shell or not. |
| |
| <p>Since some shell in wide use implement the WUE way (and some even |
| IUE), there is a considerable number of broken programs out there that |
| break WCE shells. The programmers just don't recognize it if their |
| shell isn't WCE. |
| |
| <H3>How to be a proper program</H3> |
| |
| <p>(Short note in advance: What you need to achieve is that |
| WIFSIGNALED(status) is true in the calling program and that |
| WTERMSIG(status) returns SIGINT.) |
| |
| <p>If you don't catch SIGINT, the system automatically does the right |
| thing for you: Your program exits and the calling program gets the |
| right "I-exited-on-SIGINT" status after waiting for your exit. |
| |
| <p>But once you catch SIGINT, you have to act. |
| |
| <p>Decide whether the SIGINT is used for exit/abort purposes and hence |
| a shellscript calling this program should discontinue. This is |
| hopefully obvious. If you just need to do some cleanup on SIGINT, but |
| then exit immediately, the answer is "yes". |
| |
| <p>If so, you have to tell the calling program about it by exiting |
| with the "I-exited-on-SIGINT" status. |
| |
| <p>There is no other way of doing this than to kill yourself with a |
| SIGINT signal. Do it by resetting the SIGINT handler to SIG_DFL, then |
| send yourself the signal. |
| |
| <PRE> |
| void sigint_handler(int sig) |
| { |
| <do some cleanup> |
| signal(SIGINT, SIG_DFL); |
| kill(getpid(), SIGINT); |
| } |
| </PRE> |
| |
| Notes: |
| |
| <MENU> |
| |
| <LI>You cannot "fake" the proper exit status by an exit(3) with a |
| special numeric value. People often assume this since the manuals for |
| shells often list some return value for exactly this. But this is just |
| a convention for your shell script. It does not work from one UNIX API |
| program to another. |
| |
| <P>All that happens is that the shell sets the "$?" variable to a |
| special numeric value for the convenience of your script, because your |
| script does not have access to the lower-lever UNIX status evaluation |
| functions. This is just an agreement between your script and the |
| executing shell, it does not have any meaning in other contexts. |
| |
| <P><LI>Do not use kill(0, SIGINT) without consulting the manul for |
| your OS implementation. I.e. on BSD, this would not send the signal to |
| the current process, but to all processes in the group. |
| |
| <P><LI>POSIX 1003.1 allows all these calls to appear in signal |
| handlers, so it is portable. |
| |
| </MENU> |
| |
| <p>In a bourne shell script, you can catch signals using the |
| <code>trap</code> command. Here, the same as for C programs apply. If |
| the intention of SIGINT is to end your program, you have to exit in a |
| way that the calling programs "sees" that you have been killed. If |
| you don't catch SIGINT, this happened automatically, but of you catch |
| SIGINT, i.e. to do cleanup work, you have to end the program by |
| killing yourself, not by calling exit. |
| |
| <p>Consider this example from FreeBSD's <code>mkdep</code>, which is a |
| bourne shell script. |
| |
| <pre> |
| TMP=_mkdep$$ |
| trap 'rm -f $TMP ; trap 2 ; kill -2 $$' 1 2 3 13 15 |
| </pre> |
| |
| Yes, you have to do it the hard way. It's even more annoying in shell |
| scripts than in C programs since you can't "pre-delete" temporary |
| files (which isn't really portable in C, though). |
| |
| <P>All this applies to programs in all languages, not only C and |
| bourne shell. Every language implementation that lets you catch SIGINT |
| should also give you the option to reset the signal and kill yourself. |
| |
| <P>It is always desirable to exit the right way, even if you don't |
| expect your usual callers to depend on it, some unusual one will come |
| along. This proper exit status will be needed for WCE and will not |
| hurt when the calling shell uses IUE or WUE. |
| |
| <H3>How to be a proper shell</H3> |
| |
| All this applies only for the script-executing case. Most shells will |
| also have interactive modes where things are different. |
| |
| <MENU> |
| |
| <LI>Do nothing special when SIGINT appears while you wait for a child. |
| You don't even have to remember that one happened. |
| |
| <P><LI>Wait for child to exit, get the exit status. Do not truncate it |
| to type char. |
| |
| <P><LI>Look at WIFSIGNALED(status) and WTERMSIG(status) to tell |
| whether the child says "I exited on SIGINT: in my opinion the user |
| wants the shellscript to be discontinued". |
| |
| <P><LI>If the latter applies, discontinue the script. |
| |
| <P><LI>Exit. But since a shellscript may in turn be called by a |
| shellscript, you need to make sure that you properly communicate the |
| discontinue intention to the calling program. As in any other program |
| (see above), do |
| |
| <PRE> |
| signal(SIGINT, SIG_DFL); |
| kill(getpid(), SIGINT); |
| </PRE> |
| |
| </MENU> |
| |
| <H3>Other remarks</H3> |
| |
| Although this web page talks about SIGINT only, almost the same issues |
| apply to SIGQUIT, including proper exiting by killing yourself after |
| catching the signal and proper reaction on the WIFSIGNALED(status) |
| value. One notable difference for SIGQUIT is that you have to make |
| sure that not the whole call tree dumps core. |
| |
| <H3>What to fight</H3> |
| |
| Make sure all programs <em>really</em> kill themselves if they react |
| to SIGINT or SIGQUIT and intend to abort their operation as a result |
| of this signal. Programs that don't use SIGINT/SIGQUIT as a |
| termination trigger - but as part of normal operation - don't kill |
| themselves, but do a normal exit instead. |
| |
| <p>Make sure people understand why you can't fake an exit-on-signal by |
| doing exit(...) using any numerical status. |
| |
| <p>Make sure you use a shell that behaves right. Especially if you |
| develop programs, since it will help seeing problems. |
| |
| <H3>Concrete examples how to fix programs:</H3> |
| <ul> |
| |
| <li>The fix for FreeBSD's |
| <A HREF="http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/time/time.c.diff?r1=1.10&r2=1.11">time(1)</A>. This fix is the best example, it's quite short and clear and |
| it fixes a case where someone tried to fake signal exit status by a |
| numerical value. And the complete program is small. |
| |
| <p><li>Fix for FreeBSD's |
| <A HREF="http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/truss/main.c.diff?r1=1.9&r2=1.10">truss(1)</A>. |
| |
| <p><li>The fix for FreeBSD's |
| <A HREF="http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/mkdep/mkdep.gcc.sh.diff?r1=1.8.2.1&r2=1.8.2.2">mkdep(1)</A>, a shell script. |
| |
| |
| <p><li>Fix for FreeBSD's make(1), <A HREF="http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/make/job.c.diff?r1=1.9&r2=1.10">part 1</A>, |
| <A HREF="http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/make/compat.c.diff?r1=1.10&r2=1.11">part 2</A>. |
| |
| </ul> |
| |
| <H3>Testsuite for shells</H3> |
| |
| I have a collection of shellscripts that test shells for the |
| behavior. See my <A HREF="download/">download dir</A> to get the newest |
| "sh-interrupt" files, either as a tarfile or as individual file for |
| online browsing. This isn't really documented, besides from the |
| comments the scripts echo. |
| |
| <H3>Appendix 1 - table of implementation choices</H3> |
| |
| <table border cellpadding=2> |
| |
| <tr valign=top> |
| <th>Method sign</th> |
| <th>Does what?</th> |
| <th>Example shells that implement it:</th> |
| <th>What happens when a shellscript called emacs, the user used |
| <code>C-g</code> and the script has additional commands in it?</th> |
| <th>What happens when a shellscript called emacs, the user did not use |
| <code>C-c</code> and the script has additional commands in it?</th> |
| <th>What happens if a non-interactive child catches SIGINT?</th> |
| <th>To behave properly, children must do what?</th> |
| </tr> |
| |
| <tr valign=top align=left> |
| <td>IUE</td> |
| <td>The shell executing a script exits immediately if it receives |
| SIGINT.</td> |
| <td>4.4BSD ash (ash), NetBSD, FreeBSD prior to 3.0/22.8</td> |
| <td>The editor session is lost and subsequent commands are not |
| executed.</td> |
| <td>The editor continues as normal and the subsequent commands are |
| executed. </td> |
| <td>The scripts ends immediately, returning to the caller even before |
| the current foreground child of the shell exits. </td> |
| <td>It doesn't matter what the child does or how it exits, even if the |
| child continues to operate, the shell returns. </td> |
| </tr> |
| |
| <tr valign=top align=left> |
| <td>WUE</td> |
| <td>If the shell executing a script received SIGINT while a foreground |
| process was running, it will exit after that child's exit.</td> |
| <td>pdksh (OpenBSD /bin/sh)</td> |
| <td>The editor continues as normal, but subsequent commands from the |
| script are not executed.</td> |
| <td>The editor continues as normal and subsequent commands are |
| executed. </td> |
| <td>The scripts returns to its caller after the current foreground |
| child exits, no matter how the child exited. </td> |
| <td>It doesn't matter how the child exits (signal status or not), but |
| if it doesn't return at all, the shell will not return. In no case |
| will further commands from the script be executed. </td> |
| </tr> |
| |
| <tr valign=top align=left> |
| <td>WCE</td> |
| <td>The shell exits if a child signaled that it was killed on a |
| signal (either it had the default handler for SIGINT or it killed |
| itself). </td> |
| <td>bash (Linux /bin/sh), most commercial /bin/sh, FreeBSD /bin/sh |
| from 3.0/2.2.8.</td> |
| <td>The editor continues as normal and subsequent commands are |
| executed. </td> |
| <td>The editor continues as normal and subsequent commands are |
| executed. </td> |
| <td>The scripts returns to its caller after the current foreground |
| child exits, but only if the child exited with signal status. If |
| the child did a normal exit (even if it received SIGINT, but catches |
| it), the script will continue. </td> |
| <td>The child must be implemented right, or the user will not be able |
| to break shell scripts reliably.</td> |
| </tr> |
| |
| </table> |
| |
| <P><img src=linie.png width="100%" alt=" "> |
| <BR>©2005 Martin Cracauer <cracauer @ cons.org> |
| <A HREF="http://www.cons.org/cracauer/">http://www.cons.org/cracauer/</A> |
| <BR>Last changed: $Date: 2005/02/11 21:44:43 $ |
| </BODY></HTML> |
