Re: Heredoc leading tab/space behaviour

[Kerin Millar]

Hi Gerold,

On Fri, 24 Jun 2022 13:53:07 +0200 (CEST)
"Ing. Gerold Broser" via Bug reports for the GNU Bourne Again SHell 
<bug-bash@gnu.org> wrote:

> Hello,
> 
> Configuration Information 1:
> 
> Machine: x86_64
> OS: linux-gnu
> Compiler: gcc -I/home/abuild/rpmbuild/BUILD/bash-4.3 
> -L/home/abuild/rpmbuild/BUILD/bash-4.3/../readline-6.3
> Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
> -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-suse-linux-gnu' 
> -DCONF_VENDOR='suse' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
> -DHAVE_CONFIG_H -I. -I. -I./include -I./lib -fmessage-length=0 
> -grecord-gcc-switches -fstack-protector -O2 -Wall -D_FORTIFY_SOURCE=2 
> -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -g 
> -D_GNU_SOURCE -DRECYCLES_PIDS -Wall -g -Wuninitialized -Wextra 
> -Wno-unprototyped-calls -Wno-switch-enum -Wno-unused-variable 
> -Wno-unused-parameter -Wno-parentheses -ftree-loop-linear -pipe -DBNC382214=0 
> -DIMPORT_FUNCTIONS_DEF=0 -fprofile-use
> uname output: Linux <...host name...> 4.12.14-122.116-default #1 SMP Tue Apr 
> 5 13:16:39 UTC 2022 (b42b08b) x86_64 x86_64 x86_64 GNU/Linux
> Machine Type: x86_64-suse-linux-gnu
> 
> Bash Version: 4.3
> Patch Level: 48
> Release Status: release
> 
> Configuration Information 2 (Win 10 Enterprise, Git Bash v2.34.1):
> 
> Machine: x86_64
> OS: msys
> Compiler: gcc
> Compilation CFLAGS: -DPROGRAM='bash.exe' -DCONF_HOSTTYPE='x86_64' 
> -DCONF_OSTYPE='msys' -DCONF_MACHTYPE='x86_64-pc-msys' -DCONF_VENDOR='pc' 
> -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H 
> -DRECYCLES_PIDS -I. -I. -I./include -I./lib -DWORDEXP_OPTION 
> -Wno-discarded-qualifiers -march=x86-64 -mtune=generic -O2 -pipe 
> -Wno-parentheses -Wno-format-security -D_STATIC_BUILD -g
> uname output: MINGW64_NT-10.0-19042 <...host name...> 3.1.7-340.x86_64 
> 2021-10-12 16:29 UTC x86_64 Msys
> Machine Type: x86_64-pc-msys
> 
> Bash Version: 4.4
> Patch Level: 23
> Release Status: release
> 
> 
> Description:
> 
> The Bash Reference Manual says about Heredoc's redirection operator '<<-':
> 
> "If the redirection operator is ‘<<-’, then all leading tab characters are 
> stripped from input lines and the line containing delimiter."
> – https://www.gnu.org/software/bash/manual/bash.html#Here-Documents
> 
> This is only half true since apparently also leading spaces are stripped from 
> input lines (while they are not from the delimiter line, and lead to an error 
> there).

They're not, though.

$ printf '%s\n' 'cat <<-EOF' $'\x20\x20foo' $'\t\tbar' EOF | bash | od -a
0000000  sp  sp   f   o   o  nl   b   a   r  nl
0000012

Note that the two space characters preceding foo are preserved, whereas the two 
leading tab characters preceding bar are not.

> 
> 
> Repeat-By:
> 
> ---- Note ----
> Unicode characters:
> - blank (U+2423) for space (U+20)
> and
> - tab (U+2B73) + 7 spaces for Tab (U+9)
> used for clarity in the following.
> --------------
> 
> heredoc-error.sh:
> 
> #!/bin/bash
> sed -f - heredoc-error.sh <<-SCRIPT
> ␣␣s/something/else/
> ⭲       s/more/else/
> ␣␣SCRIPT
> 
> $ . heredoc.sh
> bash: warning: here-document at line 2 delimited by end-of-file (wanted 
> `SCRIPT')
> sed: file - line 3: unknown command: `S'
> 
> 
> $ . heredoc-ok.sh
> #!/bin/bash
> sed -f - heredoc-ok.sh <<-SCRIPT
> ␣␣s/else/else/
> ⭲       s/else/else/
> ⭲       SCRIPT
> 
> 
> Fix:
> 
> I think it'd be convenient if Heredoc supports indentation with spaces at the 
> delimiter line, too.

One issue with this proposal is that it would violate the rules of the Shell 
Command Language, per 
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04.

-- 
Kerin Millar