read -r flag not working on 5.8.1

read -r flag not working on 5.8.1

[David Milum]

[-- Attachment #1: Type: text/plain, Size: 446 bytes --]

Hello, seems like the -r (raw mode) flag which should prevent it from
interpreting backslashes is not working? My understanding is the following
example shouldn't clear the "CLEAR" part. I can also demonstrate with new
lines.

$ read -r TEST
asd\c CLEAR
$ echo $TEST
asd
$ zsh --version
zsh 5.8 (x86_64-pc-linux-gnu)

According to pacman the installed version is 5.8.1

I was also able to reproduce on my mac
zsh  5.7.1 (x86_64-apple-darwin19.0)

[-- Attachment #2: Type: text/html, Size: 616 bytes --]

Re: read -r flag not working on 5.8.1

[David Milum]

[-- Attachment #1: Type: text/plain, Size: 699 bytes --]

Disregard, and apologies for the noise. I understand now -r is not the same
as in bash. Should have clued me in when it didn't work on my mac.

On Sun, Aug 8, 2021 at 1:38 AM David Milum <david.milum.89@gmail.com> wrote:

> Hello, seems like the -r (raw mode) flag which should prevent it from
> interpreting backslashes is not working? My understanding is the following
> example shouldn't clear the "CLEAR" part. I can also demonstrate with new
> lines.
>
> $ read -r TEST
> asd\c CLEAR
> $ echo $TEST
> asd
> $ zsh --version
> zsh 5.8 (x86_64-pc-linux-gnu)
>
> According to pacman the installed version is 5.8.1
>
> I was also able to reproduce on my mac
> zsh  5.7.1 (x86_64-apple-darwin19.0)
>

[-- Attachment #2: Type: text/html, Size: 1126 bytes --]

Re: read -r flag not working on 5.8.1

[Mikael Magnusson]

On 8/8/21, David Milum <david.milum.89@gmail.com> wrote:
> Disregard, and apologies for the noise. I understand now -r is not the same
> as in bash. Should have clued me in when it didn't work on my mac.
>
> On Sun, Aug 8, 2021 at 1:38 AM David Milum <david.milum.89@gmail.com>
> wrote:
>
>> Hello, seems like the -r (raw mode) flag which should prevent it from
>> interpreting backslashes is not working? My understanding is the
>> following
>> example shouldn't clear the "CLEAR" part. I can also demonstrate with new
>> lines.
>>
>> $ read -r TEST
>> asd\c CLEAR
>> $ echo $TEST
>> asd
>> $ zsh --version
>> zsh 5.8 (x86_64-pc-linux-gnu)

Your problem is not read, but echo. Try the above with echo -E $TEST
instead and you will see the read command is fine.

-- 
Mikael Magnusson

Re: read -r flag not working on 5.8.1

[Stephane Chazelas]

2021-08-08 07:59:20 +0200, Mikael Magnusson:
[...]
> >> Hello, seems like the -r (raw mode) flag which should prevent it from
> >> interpreting backslashes is not working? My understanding is the
> >> following
> >> example shouldn't clear the "CLEAR" part. I can also demonstrate with new
> >> lines.
> >>
> >> $ read -r TEST
> >> asd\c CLEAR
> >> $ echo $TEST
> >> asd
> >> $ zsh --version
> >> zsh 5.8 (x86_64-pc-linux-gnu)
> 
> Your problem is not read, but echo. Try the above with echo -E $TEST
> instead and you will see the read command is fine.
[...]

More precisely, to print the contents of a scalar variable
verbatim followed by a newline character in zsh:

echo -E - $var # zsh only
print -r - $var # zsh
print -r -- $var # zsh
print -r - "$var" # zsh/ksh
printf '%s\n' "$var" # POSIX
echo -En "$var"$'\n' # zsh/bash and a few other echo
		     # implementations (but for bash, not if
		     # both the xpg_echo and posix options are
		     # enabled).
cat << EOF  # Bourne/POSIX
$var
EOF
cat <<< "$var" # zsh and a few other shells

See also

zmodload zsh/system
syswrite -- "$var"$'\n' ||
  syserror -p failed: $ERRNO

for a raw interface to the write() system call.

And btw, to read a line into a variable, the syntax is

IFS= read -r var

(in zsh or any other POSIX shell, though only zsh can read lines
containing NUL bytes).

See

https://unix.stackexchange.com/questions/65803/why-is-printf-better-than-echo
https://unix.stackexchange.com/questions/209123/understanding-ifs-read-r-line

-- 
Stephane