Re: NL character removed after \\ in command substitution

[Andreas Kusalananda Kähäri]

On Tue, Aug 17, 2021 at 08:32:35AM +0200, Kusalananda Kähäri wrote:
> On Tue, Aug 17, 2021 at 10:28:16AM +0800, Haojun Bao wrote:
> > Configuration Information [Automatically generated, do not change]:
> > Machine: x86_64
> > OS: linux-gnu
> > Compiler: gcc
> > Compilation CFLAGS: -g -O2
> > -fdebug-prefix-map=/build/bash-2bxm7h/bash-5.0=.
> > -fstack-protector-strong -Wformat -Werror=format-security -Wall
> > -Wno-parentheses -Wno-format-security
> > uname output: Linux bhj-pc1 5.10.0-0.bpo.5-amd64 #1 SMP Debian
> > 5.10.24-1~bpo10+1 (2021-03-29) x86_64 GNU/Linux
> > Machine Type: x86_64-pc-linux-gnu
> > 
> > Bash Version: 5.0
> > Patch Level: 3
> > Release Status: release
> > 
> > Description:
> > 
> > A bug found in parse.y, that will treat reading of COMMAND and
> > $(COMMAND) differently, despite the info manual saying that:
> > 
> > > When the old-style backquote form of substitution is used, backslash
> > > retains its literal meaning except when followed by '$', '`', or '\'.
> > > The first backquote not preceded by a backslash terminates the command
> > > substitution.  When using the '$(COMMAND)' form, all characters between
> > > the parentheses make up the command; none are treated specially.
> > 
> > It seems the NL after \\ will be removed when run as $(COMMAND) in parse.y?
> > 
> > Repeat-By:
> > 
> > This command will output $'hello \\\nworld\n':
> > 
> > cat <<EOF
> > hello \\
> > world
> > EOF
> > 
> > This command will output $'hello \\world\n' (missing the \n after \\):
> > echo "$(
> > cat <<EOF
> > hello \\
> > world
> > EOF
> > )"
> 
> 
> Consider quoting the here-document:
> 
>       cat <<'EOF'
>       hello \\
>       world
>       EOF
>       )"
> 

The initial line saying

        echo "$(

was obviously missing there (copy+paste error), sorry.


-- 
Andreas (Kusalananda) Kähäri
SciLifeLab, NBIS, ICM
Uppsala University, Sweden

.