threads / discuss / 14930
Subject: git-bisect: weird usage of read(1)
Hello
I found this in git bisect:
printf >&2 'Are you sure [Y/n]? '
case "$(read yesno)" in [Nn]*) exit 1 ;; esacwhich looks very weird since read(1) returns a status and not the string reads from std input.
Am I missing something ?
Thanks
-- Francis
Johannes SchindelinRe: git-bisect: weird usage of read(1)
Hi,
On Mon, 11 Aug 2008, Francis Moreau wrote:
> I found this in git bisect: > > printf >&2 'Are you sure [Y/n]? ' > case "$(read yesno)" in [Nn]*) exit 1 ;; esac > > which looks very weird since read(1) returns a status and not the > string reads from std input. > > Am I missing something ?
Yes. "$()" does not return the status, but the output.
Ciao, Dscho
Re: git-bisect: weird usage of read(1)
2008/8/11 Johannes Schindelin <Johannes.Schindelin@gmx.de>:
> Hi, > > On Mon, 11 Aug 2008, Francis Moreau wrote: > >> I found this in git bisect: >> >> printf >&2 'Are you sure [Y/n]? ' >> case "$(read yesno)" in [Nn]*) exit 1 ;; esac >> >> which looks very weird since read(1) returns a status and not the >> string reads from std input. >> >> Am I missing something ? > > Yes. "$()" does not return the status, but the output.
But there is no output, since read doesn't print anything... case "$(read yesno; echo $yesno)" in [Nn]*) could work, but looks a bit strange. read yesno; case $yesno in [Nn]*) would be the usual way to do things i think?
-- Mikael Magnusson
Re: git-bisect: weird usage of read(1)
Hello
On Mon, Aug 11, 2008 at 4:15 PM, Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> Hi, > > On Mon, 11 Aug 2008, Francis Moreau wrote: > >> I found this in git bisect: >> >> printf >&2 'Are you sure [Y/n]? ' >> case "$(read yesno)" in [Nn]*) exit 1 ;; esac >> >> which looks very weird since read(1) returns a status and not the >> string reads from std input. >>
sorry I should have said that there's a status but no output...
>> Am I missing something ? > > Yes. "$()" does not return the status, but the output. >
But what's the output in that case ?
-- Francis
Re: git-bisect: weird usage of read(1)
2008/8/11 Francis Moreau <francis.moro@gmail.com>:
> Hello > > On Mon, Aug 11, 2008 at 4:15 PM, Johannes Schindelin > <Johannes.Schindelin@gmx.de> wrote: >> Hi, >> >> On Mon, 11 Aug 2008, Francis Moreau wrote: >> >>> I found this in git bisect: >>> >>> printf >&2 'Are you sure [Y/n]? ' >>> case "$(read yesno)" in [Nn]*) exit 1 ;; esac >>> >>> which looks very weird since read(1) returns a status and not the >>> string reads from std input. >>> > > sorry I should have said that there's a status but no output... > >>> Am I missing something ? >> >> Yes. "$()" does not return the status, but the output. >> > > But what's the output in that case ?
Using cygwin+bash, I get:
$ echo $(read yesno) n
$ echo $(read yesno; echo $yesno) n n $ $(read yesno) && echo yes || echo no n yes $ $(read yesno) && echo yes || echo no y yes $ case "$(read yesno)" in [Nn]*) echo "no" ;; esac n $ case "$(read yesno)" in [Nn]*) echo "no" ;; esac y $ case "$(read yesno; echo $yesno)" in [Nn]*) echo "no" ;; esac n no $ case "$(read yesno; echo $yesno)" in [Nn]*) echo "no" ;; esac y
So
>>> case "$(read yesno)" in [Nn]*) exit 1 ;; esac
does not work as expected. Replacing this with
case "$(read yesno; echo $yesno)" in [Nn]*) exit 1 ;; esac
would work as intended, as Mikael has pointed out.
- Reece
Re: git-bisect: weird usage of read(1)
On Mon, Aug 11, 2008 at 5:59 PM, Reece Dunn <msclrhd@googlemail.com> wrote:
> $ $(read yesno) && echo yes || echo no > n > yes > $ $(read yesno) && echo yes || echo no > y > yes
funny, seeing these 2 cases I'm wondering why Bash is not complaining...
-- Francis
Re: git-bisect: weird usage of read(1)
2008/8/11 Francis Moreau <francis.moro@gmail.com>:
> On Mon, Aug 11, 2008 at 5:59 PM, Reece Dunn <msclrhd@googlemail.com> wrote: >> $ $(read yesno) && echo yes || echo no >> n >> yes >> $ $(read yesno) && echo yes || echo no >> y >> yes > > funny, seeing these 2 cases I'm wondering why Bash is not complaining...
I don't know; it could be an issue with cygwin.
I'll try it on a Linux box later and post the results then for comparison.
- Reece
Re: git-bisect: weird usage of read(1)
On Mon, Aug 11, 2008 at 6:26 PM, Reece Dunn <msclrhd@googlemail.com> wrote:
> 2008/8/11 Francis Moreau <francis.moro@gmail.com>: >> On Mon, Aug 11, 2008 at 5:59 PM, Reece Dunn <msclrhd@googlemail.com> wrote: >>> $ $(read yesno) && echo yes || echo no >>> n >>> yes >>> $ $(read yesno) && echo yes || echo no >>> y >>> yes >> >> funny, seeing these 2 cases I'm wondering why Bash is not complaining... > > I don't know; it could be an issue with cygwin. > > I'll try it on a Linux box later and post the results then for comparison. >
I got the same result on Linux...
-- Francis
Petr BaudisRe: git-bisect: weird usage of read(1)
On Mon, Aug 11, 2008 at 04:59:32PM +0100, Reece Dunn wrote:
> >> On Mon, 11 Aug 2008, Francis Moreau wrote: > >>> case "$(read yesno)" in [Nn]*) exit 1 ;; esac > > does not work as expected. Replacing this with > > case "$(read yesno; echo $yesno)" in [Nn]*) exit 1 ;; esac > > would work as intended, as Mikael has pointed out.
Wouldn't it be more elegant to
case "$(head -n 1)" in [Nn]*) exit 1 ;; esac
Petr "Pasky" Baudis
René ScharfeRe: git-bisect: weird usage of read(1)
Petr Baudis schrieb:
> On Mon, Aug 11, 2008 at 04:59:32PM +0100, Reece Dunn wrote: >>>> On Mon, 11 Aug 2008, Francis Moreau wrote: >>>>> case "$(read yesno)" in [Nn]*) exit 1 ;; esac >> does not work as expected. Replacing this with >> >> case "$(read yesno; echo $yesno)" in [Nn]*) exit 1 ;; esac >> >> would work as intended, as Mikael has pointed out. > > Wouldn't it be more elegant to > > case "$(head -n 1)" in [Nn]*) exit 1 ;; esac
Only if head is a built-in, otherwise you fork needlessly. Not that this is a performance critical part, but I wouldn't call it "elegant".
What's wrong with the following variant, already used a few lines up in the file?
read yesno case "$yesno" in [Nn]*) exit 1 ;; esac
René
Petr BaudisRe: git-bisect: weird usage of read(1)
On Mon, Aug 11, 2008 at 07:01:15PM +0200, René Scharfe wrote:
> Petr Baudis schrieb: > > On Mon, Aug 11, 2008 at 04:59:32PM +0100, Reece Dunn wrote: > >>>> On Mon, 11 Aug 2008, Francis Moreau wrote: > >>>>> case "$(read yesno)" in [Nn]*) exit 1 ;; esac > >> does not work as expected. Replacing this with > >> > >> case "$(read yesno; echo $yesno)" in [Nn]*) exit 1 ;; esac > >> > >> would work as intended, as Mikael has pointed out. > > > > Wouldn't it be more elegant to > > > > case "$(head -n 1)" in [Nn]*) exit 1 ;; esac > > Only if head is a built-in, otherwise you fork needlessly. Not that > this is a performance critical part, but I wouldn't call it "elegant".
Ok, exec head -n 1. ;) And yes, I know... I guess I've just spent too much time perl-golfing lately.
> What's wrong with the following variant, already used a few lines up in > the file? > > read yesno > case "$yesno" in [Nn]*) exit 1 ;; esac
Nothing wrong with this one, of course.
-- Petr "Pasky" Baudis The next generation of interesting software will be done on the Macintosh, not the IBM PC. -- Bill Gates
Junio C HamanoRe: git-bisect: weird usage of read(1)
René Scharfe <rene.scharfe@lsrfire.ath.cx> writes:
> Petr Baudis schrieb: >> On Mon, Aug 11, 2008 at 04:59:32PM +0100, Reece Dunn wrote: >>>>> On Mon, 11 Aug 2008, Francis Moreau wrote: >>>>>> case "$(read yesno)" in [Nn]*) exit 1 ;; esac >>> does not work as expected. Replacing this with >>> >>> case "$(read yesno; echo $yesno)" in [Nn]*) exit 1 ;; esac >>> >>> would work as intended, as Mikael has pointed out. >> >> Wouldn't it be more elegant to >> >> case "$(head -n 1)" in [Nn]*) exit 1 ;; esac > > Only if head is a built-in, otherwise you fork needlessly. Not that > this is a performance critical part, but I wouldn't call it "elegant". > > What's wrong with the following variant, already used a few lines up in > the file? > > read yesno > case "$yesno" in [Nn]*) exit 1 ;; esac
That's the right way to spell it. Sorry, I must have been too tired when I did this.
Re: git-bisect: weird usage of read(1)
On Mon, Aug 11, 2008 at 8:59 PM, Junio C Hamano <gitster@pobox.com> wrote:
> René Scharfe <rene.scharfe@lsrfire.ath.cx> writes: > >> Petr Baudis schrieb: >>> On Mon, Aug 11, 2008 at 04:59:32PM +0100, Reece Dunn wrote: >>>>>> On Mon, 11 Aug 2008, Francis Moreau wrote: >>>>>>> case "$(read yesno)" in [Nn]*) exit 1 ;; esac >>>> does not work as expected. Replacing this with >>>> >>>> case "$(read yesno; echo $yesno)" in [Nn]*) exit 1 ;; esac >>>> >>>> would work as intended, as Mikael has pointed out. >>> >>> Wouldn't it be more elegant to >>> >>> case "$(head -n 1)" in [Nn]*) exit 1 ;; esac >> >> Only if head is a built-in, otherwise you fork needlessly. Not that >> this is a performance critical part, but I wouldn't call it "elegant". >> >> What's wrong with the following variant, already used a few lines up in >> the file? >> >> read yesno >> case "$yesno" in [Nn]*) exit 1 ;; esac > > That's the right way to spell it. Sorry, I must have been too tired > when I did this. > > >
I sent a patch to fix that way already
Cheers.
-- Francis
René ScharfeRe: git-bisect: weird usage of read(1)
Francis Moreau schrieb:
> I found this in git bisect: > > printf >&2 'Are you sure [Y/n]? ' > case "$(read yesno)" in [Nn]*) exit 1 ;; esac > > which looks very weird since read(1) returns a status and not the > string reads from std input.
Good catch. You need to press Ctrl-C in order to exit, answering "no" means the same as "yes" here -- not very nice. Care to send a patch?
Thanks, René
Re: git-bisect: weird usage of read(1)
On Mon, Aug 11, 2008 at 6:18 PM, René Scharfe <rene.scharfe@lsrfire.ath.cx> wrote:
> Francis Moreau schrieb: >> I found this in git bisect: >> >> printf >&2 'Are you sure [Y/n]? ' >> case "$(read yesno)" in [Nn]*) exit 1 ;; esac >> >> which looks very weird since read(1) returns a status and not the >> string reads from std input. > > Good catch. You need to press Ctrl-C in order to exit, answering "no" > means the same as "yes" here -- not very nice. Care to send a patch? >
done.
-- Francis