Re: bin/12578: `` subshell taints PWD
Niall Smart wrote in list.freebsd-hackers: > > > I'm not sure if XPG4v2 requires command substitution to behave > > like that. At least, both Solaris' and DEC UNIX... oops... > > True64 UNIX do execute all command substitutions in a subshell > > (`pwd` does not affect the surrounding shell), and both claim > > XPG4 compliance. > > They only execute a subshell when they need to: No, it _always_ spawns a subshell. > $ echo $$ `echo $$` > 14405 14405 > $ uname -a > SunOS molotov.boi.ie 5.6 Generic_105181-05 sun4u sparc SUNW,Ultra-5_10 That doesn't prove anything, because $$ always contains the PID of the "top-level" shell, as I explained in an earlier mail. Try this one: $ echo $$ `( /bin/echo $$ )` 14762 14762 I think you agree that a subshell is spawned in that case, don't you? ;-) Regards Oliver -- Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany (Info: finger userinfo:o...@dorifer.heim3.tu-clausthal.de) "In jedem Stück Kohle wartet ein Diamant auf seine Geburt" (Terry Pratchett) To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Niall Smart wrote in list.freebsd-hackers: > > > I'm not sure if XPG4v2 requires command substitution to behave > > like that. At least, both Solaris' and DEC UNIX... oops... > > True64 UNIX do execute all command substitutions in a subshell > > (`pwd` does not affect the surrounding shell), and both claim > > XPG4 compliance. > > They only execute a subshell when they need to: No, it _always_ spawns a subshell. > $ echo $$ `echo $$` > 14405 14405 > $ uname -a > SunOS molotov.boi.ie 5.6 Generic_105181-05 sun4u sparc SUNW,Ultra-5_10 That doesn't prove anything, because $$ always contains the PID of the "top-level" shell, as I explained in an earlier mail. Try this one: $ echo $$ `( /bin/echo $$ )` 14762 14762 I think you agree that a subshell is spawned in that case, don't you? ;-) Regards Oliver -- Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany (Info: finger userinfo:[EMAIL PROTECTED]) "In jedem Stück Kohle wartet ein Diamant auf seine Geburt" (Terry Pratchett) To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
> I'm not sure if XPG4v2 requires command substitution to behave > like that. At least, both Solaris' and DEC UNIX... oops... > True64 UNIX do execute all command substitutions in a subshell > (`pwd` does not affect the surrounding shell), and both claim > XPG4 compliance. They only execute a subshell when they need to: $ echo $$ `echo $$` 14405 14405 $ uname -a SunOS molotov.boi.ie 5.6 Generic_105181-05 sun4u sparc SUNW,Ultra-5_10 Regards, Niall To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
> I'm not sure if XPG4v2 requires command substitution to behave > like that. At least, both Solaris' and DEC UNIX... oops... > True64 UNIX do execute all command substitutions in a subshell > (`pwd` does not affect the surrounding shell), and both claim > XPG4 compliance. They only execute a subshell when they need to: $ echo $$ `echo $$` 14405 14405 $ uname -a SunOS molotov.boi.ie 5.6 Generic_105181-05 sun4u sparc SUNW,Ultra-5_10 Regards, Niall To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
On Tue, 13 Jul 1999, Oliver Fromme wrote: > > But isn't that exactly what's happening here, where PWD is being tainted > > by the commands evaluated within the substitution? > > Yes, I'd call that a bug which should be fixed. > The manpage clearly says: > > "The shell expands the command substitution by executing > command in a subshell environment and replacing the command > substitution with the standard output of the command [...]" > > Alternatively, the manpage could be "fixed". ;-) The correct way to fix the problem is to bring our sh in line with posix in this respect. Someone more familiar with the spec than I could tell you for sure, however I can say with relative security that subshell processes should not taint parent shell variables. Exercising my firm grasp of the obvious, Doug -- On account of being a democracy and run by the people, we are the only nation in the world that has to keep a government four years, no matter what it does. -- Will Rogers To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Sheldon Hearn wrote in list.freebsd-hackers: > On Tue, 13 Jul 1999 18:13:42 +0200, Oliver Fromme wrote: > > > Command substitution certainly has to spawn a subshell, even > > for built-in commands, because otherwise you could modify > > parent shell variables within command substitutions. > > But isn't that exactly what's happening here, where PWD is being tainted > by the commands evaluated within the substitution? Yes, I'd call that a bug which should be fixed. The manpage clearly says: "The shell expands the command substitution by executing command in a subshell environment and replacing the command substitution with the standard output of the command [...]" Alternatively, the manpage could be "fixed". ;-) I'm not sure if XPG4v2 requires command substitution to behave like that. At least, both Solaris' and DEC UNIX... oops... True64 UNIX do execute all command substitutions in a subshell (`pwd` does not affect the surrounding shell), and both claim XPG4 compliance. Therefore I think the right thing to do is to fix FreeBSD's sh to always execute command substitutions in a subshell. Regards Oliver -- Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany (Info: finger userinfo:o...@dorifer.heim3.tu-clausthal.de) "In jedem Stück Kohle wartet ein Diamant auf seine Geburt" (Terry Pratchett) To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
On Tue, 13 Jul 1999, Oliver Fromme wrote: > > But isn't that exactly what's happening here, where PWD is being tainted > > by the commands evaluated within the substitution? > > Yes, I'd call that a bug which should be fixed. > The manpage clearly says: > > "The shell expands the command substitution by executing > command in a subshell environment and replacing the command > substitution with the standard output of the command [...]" > > Alternatively, the manpage could be "fixed". ;-) The correct way to fix the problem is to bring our sh in line with posix in this respect. Someone more familiar with the spec than I could tell you for sure, however I can say with relative security that subshell processes should not taint parent shell variables. Exercising my firm grasp of the obvious, Doug -- On account of being a democracy and run by the people, we are the only nation in the world that has to keep a government four years, no matter what it does. -- Will Rogers To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Sheldon Hearn wrote in list.freebsd-hackers: > On Tue, 13 Jul 1999 18:13:42 +0200, Oliver Fromme wrote: > > > Command substitution certainly has to spawn a subshell, even > > for built-in commands, because otherwise you could modify > > parent shell variables within command substitutions. > > But isn't that exactly what's happening here, where PWD is being tainted > by the commands evaluated within the substitution? Yes, I'd call that a bug which should be fixed. The manpage clearly says: "The shell expands the command substitution by executing command in a subshell environment and replacing the command substitution with the standard output of the command [...]" Alternatively, the manpage could be "fixed". ;-) I'm not sure if XPG4v2 requires command substitution to behave like that. At least, both Solaris' and DEC UNIX... oops... True64 UNIX do execute all command substitutions in a subshell (`pwd` does not affect the surrounding shell), and both claim XPG4 compliance. Therefore I think the right thing to do is to fix FreeBSD's sh to always execute command substitutions in a subshell. Regards Oliver -- Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany (Info: finger userinfo:[EMAIL PROTECTED]) "In jedem Stück Kohle wartet ein Diamant auf seine Geburt" (Terry Pratchett) To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
On Tue, 13 Jul 1999 18:13:42 +0200, Oliver Fromme wrote: > Command substitution certainly has to spawn a subshell, even > for built-in commands, because otherwise you could modify > parent shell variables within command substitutions. But isn't that exactly what's happening here, where PWD is being tainted by the commands evaluated within the substitution? Ciao, Sheldon. To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Niall Smart wrote in list.freebsd-hackers: > As I understand it most builtins will not spawn a new shell > when they are used in command substitution: > > niall% echo `echo $$` $$ > 20354 20354 > niall% Actually, that example doesn't prove anything. :-) $ echo `echo $$` $$ 8376 8376 $ echo `/bin/echo $$` $$ 8376 8376 $ echo `(/bin/echo $$)` $$ 8376 8376 $ echo `eval /bin/echo '$$'` $$ 8376 8376 $ echo `(eval /bin/echo '$$')` $$ 8376 8376 $ At first I thought that behaviour would be a bug, but it isn't. sh(1) says: $Expands to the process ID of the invoked shell. A subshell retains the same value of $ as its parent. I.e. $$ does not change when a subshell is spawned, but it rather inherits the value of $$ from its parent. This makes sense, because it enables you to use constructs like this in shell scripts: touch tmp.$$ chmod 600 tmp.$$ ls | grep foo | while read file; do something ... >> tmp.$$# <-- subshell! done do_more_things < tmp.$$ Command substitution certainly has to spawn a subshell, even for built-in commands, because otherwise you could modify parent shell variables within command substitutions. You can easily verify this with ktrace. ;-) Regards Oliver -- Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany (Info: finger userinfo:o...@dorifer.heim3.tu-clausthal.de) "In jedem Stück Kohle wartet ein Diamant auf seine Geburt" (Terry Pratchett) To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
On Tue, 13 Jul 1999 18:13:42 +0200, Oliver Fromme wrote: > Command substitution certainly has to spawn a subshell, even > for built-in commands, because otherwise you could modify > parent shell variables within command substitutions. But isn't that exactly what's happening here, where PWD is being tainted by the commands evaluated within the substitution? Ciao, Sheldon. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Niall Smart wrote in list.freebsd-hackers: > As I understand it most builtins will not spawn a new shell > when they are used in command substitution: > > niall% echo `echo $$` $$ > 20354 20354 > niall% Actually, that example doesn't prove anything. :-) $ echo `echo $$` $$ 8376 8376 $ echo `/bin/echo $$` $$ 8376 8376 $ echo `(/bin/echo $$)` $$ 8376 8376 $ echo `eval /bin/echo '$$'` $$ 8376 8376 $ echo `(eval /bin/echo '$$')` $$ 8376 8376 $ At first I thought that behaviour would be a bug, but it isn't. sh(1) says: $Expands to the process ID of the invoked shell. A subshell retains the same value of $ as its parent. I.e. $$ does not change when a subshell is spawned, but it rather inherits the value of $$ from its parent. This makes sense, because it enables you to use constructs like this in shell scripts: touch tmp.$$ chmod 600 tmp.$$ ls | grep foo | while read file; do something ... >> tmp.$$# <-- subshell! done do_more_things < tmp.$$ Command substitution certainly has to spawn a subshell, even for built-in commands, because otherwise you could modify parent shell variables within command substitutions. You can easily verify this with ktrace. ;-) Regards Oliver -- Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany (Info: finger userinfo:[EMAIL PROTECTED]) "In jedem Stück Kohle wartet ein Diamant auf seine Geburt" (Terry Pratchett) To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Sheldon Hearn wrote: > > On Mon, 12 Jul 1999 18:37:13 GMT, Niall Smart wrote: > > > The patch appended seems to fix this, I'd like someone familiar > > with sh to review it though, since this may be symptomatic of > > a general problem with command substitution. > > As I understand your patch, you're saying "we should fork off a child > process when the command in question is cd"? This is what I missed when > I tried ``echo .`sleep 600`.'' and assumed that the result was proof > that we always spawn a subprocess for backtick evaluation. :-( As I understand it most builtins will not spawn a new shell when they are used in command substitution: niall% echo `echo $$` $$ 20354 20354 niall% Niall To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Sheldon Hearn wrote: > > On Mon, 12 Jul 1999 18:37:13 GMT, Niall Smart wrote: > > > The patch appended seems to fix this, I'd like someone familiar > > with sh to review it though, since this may be symptomatic of > > a general problem with command substitution. > > As I understand your patch, you're saying "we should fork off a child > process when the command in question is cd"? This is what I missed when > I tried ``echo .`sleep 600`.'' and assumed that the result was proof > that we always spawn a subprocess for backtick evaluation. :-( As I understand it most builtins will not spawn a new shell when they are used in command substitution: niall% echo `echo $$` $$ 20354 20354 niall% Niall To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
On Mon, 12 Jul 1999 18:37:13 GMT, Niall Smart wrote: > The patch appended seems to fix this, I'd like someone familiar > with sh to review it though, since this may be symptomatic of > a general problem with command substitution. As I understand your patch, you're saying "we should fork off a child process when the command in question is cd"? This is what I missed when I tried ``echo .`sleep 600`.'' and assumed that the result was proof that we always spawn a subprocess for backtick evaluation. :-( Ciao, Sheldon. To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Sheldon Hearn wrote:
> cd /tmp
> echo .`cd /`.
> pwd
>
> Any takers?
The patch appended seems to fix this, I'd like someone familiar
with sh to review it though, since this may be symptomatic of
a general problem with command substitution.
> PS: And no, this is not an invitation to chat about the default shell
> for the base system. :-)
You're hinting it should be /bin/sh for root, right?
Regards,
Niall
*** eval.c~ Mon May 10 16:10:16 1999
--- eval.c Mon Jul 12 18:27:44 1999
***
*** 710,715
--- 710,716
&& ((flags & EV_EXIT) == 0 || Tflag))
|| ((flags & EV_BACKCMD) != 0
&& (cmdentry.cmdtype != CMDBUILTIN
+|| cmdentry.u.index == CDCMD
|| cmdentry.u.index == DOTCMD
|| cmdentry.u.index == EVALCMD))) {
jp = makejob(cmd, 1);
To Unsubscribe: send mail to majord...@freebsd.org
with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
On Mon, 12 Jul 1999 18:37:13 GMT, Niall Smart wrote: > The patch appended seems to fix this, I'd like someone familiar > with sh to review it though, since this may be symptomatic of > a general problem with command substitution. As I understand your patch, you're saying "we should fork off a child process when the command in question is cd"? This is what I missed when I tried ``echo .`sleep 600`.'' and assumed that the result was proof that we always spawn a subprocess for backtick evaluation. :-( Ciao, Sheldon. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Sheldon Hearn wrote:
> cd /tmp
> echo .`cd /`.
> pwd
>
> Any takers?
The patch appended seems to fix this, I'd like someone familiar
with sh to review it though, since this may be symptomatic of
a general problem with command substitution.
> PS: And no, this is not an invitation to chat about the default shell
> for the base system. :-)
You're hinting it should be /bin/sh for root, right?
Regards,
Niall
*** eval.c~ Mon May 10 16:10:16 1999
--- eval.c Mon Jul 12 18:27:44 1999
***
*** 710,715
--- 710,716
&& ((flags & EV_EXIT) == 0 || Tflag))
|| ((flags & EV_BACKCMD) != 0
&& (cmdentry.cmdtype != CMDBUILTIN
+|| cmdentry.u.index == CDCMD
|| cmdentry.u.index == DOTCMD
|| cmdentry.u.index == EVALCMD))) {
jp = makejob(cmd, 1);
To Unsubscribe: send mail to [EMAIL PROTECTED]
with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Hi folks, I'm hoping someone here is interested in tracking down a bug in our /bin/sh . Changing directory within a backtick (``) subshell in sh taints the parent's working directory. The following sample code gives the expected result for /bin/csh, but breaks for /bin/sh cd /tmp echo .`cd /`. pwd Any takers? Ciao, Sheldon. PS: And no, this is not an invitation to chat about the default shell for the base system. :-) PPS: S! PPPS: www.s.com To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
Re: bin/12578: `` subshell taints PWD
Hi folks, I'm hoping someone here is interested in tracking down a bug in our /bin/sh . Changing directory within a backtick (``) subshell in sh taints the parent's working directory. The following sample code gives the expected result for /bin/csh, but breaks for /bin/sh cd /tmp echo .`cd /`. pwd Any takers? Ciao, Sheldon. PS: And no, this is not an invitation to chat about the default shell for the base system. :-) PPS: S! PPPS: www.s.com To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
