Re: magic/absurd bash interpreter/compiler ?

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From	Barry Margolin <barmar@alum.mit.edu>
Newsgroups	comp.compilers, comp.unix.shell, comp.os.linux.misc
Subject	Re: magic/absurd bash interpreter/compiler ?
Date	Fri, 28 Dec 2012 10:25:33 -0500
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glen herrmannsfeldt <gah@ugcs.caltech.edu> wrote:
> In comp.compilers Eric <eric@deptj.eu> wrote:
>
> (snip, I wrote)
> >> One problem with many unix shells is that redirection is done too early.
> >> Specifically, before an if test is done.
>
> > I am tempted to think that this is a conceptual misunderstanding, so an
> > example would be useful.
>
> From the man page for csh:
>
>   "The single-command form of if does output redirection even if the
>    expression is false and  the  command is not executed."
>
> echo false > file
> if( 1 > 2 ) echo true > file
>
> The if statement will open (and truncate) file before
> testing the condition. At least for csh, I didn't try others.
>
> -- glen
> [That's one of the many, many bugs in csh.  In posix shells such as
> sh and bash, they do what you'd expect:
>
> if [ 1 \> 2 ]; then echo true > file; fi   # doesn't create the file
> if [ 1 \> 2 ]; then echo true; fi > file   # does create it
>
> -John]

csh is so broken, it's best ignored when talking about "Unix shells" in
general.  Even more so when someone says "many Unix shells", since one
exception hardly counts as "many".

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
[Several other people wrote to agree that csh is bad news. -John]

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magic/absurd bash interpreter/compiler ? Avoid9Pdf@gmail.com - 2012-12-23 11:04 +0000
  Re: magic/absurd bash interpreter/compiler ? J G Miller <miller@yoyo.ORG> - 2012-12-24 00:28 +0000
  Re: magic/absurd bash interpreter/compiler ? "Jonathan Thornburg" <jthorn@astro.indiana.edu> - 2012-12-24 03:57 +0000
  Re: magic/absurd bash interpreter/compiler ? Eric <eric@deptj.eu> - 2012-12-24 19:13 +0000
    Re: magic/absurd bash interpreter/compiler ? Barry Margolin <barmar@alum.mit.edu> - 2012-12-24 20:48 -0500
    Re: magic/absurd bash interpreter/compiler ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-25 03:25 +0000
      Re: magic/absurd bash interpreter/compiler ? Eric <eric@deptj.eu> - 2012-12-26 12:51 +0000
        Re: magic/absurd bash interpreter/compiler ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-28 03:17 +0000
          Re: magic/absurd bash interpreter/compiler ? Barry Margolin <barmar@alum.mit.edu> - 2012-12-28 10:25 -0500

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