Re: [Help-bash] confusion of shell's new option compat41

[MaShimiao]

On 01/17/2013 03:42 AM, Chet Ramey wrote:
> On 1/16/13 1:06 PM, Ma Shimiao wrote:
> > According to changelog and manpage, I find compat as a new option is added.
> > I have read manpage for many times. But I actually can't find out what it
> > affects.
> > And I don't understand what special character means.
> >
> > ManPage as follow:
> > compat41
> >              If set, bash, when in posix mode, treats a single quote in a dou‐
> >              ble-quoted  parameter expansion as a special character.  The sin‐
> >              gle quotes must match (an even number) and the characters between
> >              the single quotes are considered quoted.  This is the behavior of
> >              posix mode  through  version  4.1.   The  default  bash  behavior
> >              remains as in previous versions.
> >
> > Could someone give me a example shows how to use compat41?
> Look at what a bash-4.2 instance running in Posix mode does with this:
>
> echo "${HOME+'foo}"
>
> with and without compat41 enabled.
I test in Fedora16 and bash-4.2.28. there is nothing difference.

First, I wrote a script :
#!/bin/bash
shopt -s compat41
echo "${HOME+'foo}"

then, run it:
#  bash --posix compat.sh
'foo

Second, I changed the script:
#!/bin/bash
shopt -u compat41
echo "${HOME+'foo}"

then, run it:
#  bash --posix compat.sh
'foo
> The compat41 option changes how this construct is expanded.  With it
> enabled, the single quote is special: it is a quote character, must have
> an open and close quote, and results in the characters between the single
> quotes being sort-of quoted.
>
> I changed bash-4.2 posix mode to conform to a post-bash-4.1 Posix
> interpretation.  That interpretation put the burden of matching quotes on
> the application, changed single quotes to be ordinary characters in a
> double-quoted word expansion, and removed the requirement that the shell
> ensure they match.
>
> The default bash behavior doesn't change: it requires that the single
> quotes match.
>
> Chet