dash & IFS

dash & IFS

[n8dandy]

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Good morning,

Few days ago, I noticed something strange with dash and IFS. It was
verified with the following versions :

- 0.5.10.2 on Voidlinux
- 0.5.10.2 on Debian Buster
- 0.5.8 on Ubuntu 18.04.2 LTS (Bionic Beaver)

Here the issue :

$ ls
file.sign  file1  file2  other.sign  whileifs*
$ cat whileifs
#!/bin/dash

find . -type f | sort -d | while IFS=$'\n' read -r F; do
	printf "%s\n" "$F"
done
$ ./whileifs
./file1
./file2
./file.sig
./other.sig
./whileifs

file.sig and other.sig are returned instead of file.sign and other.sign.

Here the result with bash :
$ bash whileifs
./file1
./file2
./file.sign
./other.sign
./whileifs

Here the result with mksh :
$ mksh whileifs
./file1
./file2
./file.sign
./other.sign
./whileifs

Here the result with lksh :
$ lksh whileifs
./file1
./file2
./file.sign
./other.sign
./whileifs

Here the result with busybox ash (1.31.0) :
$ /tmp/busybox-x86_64 ash whileifs
./file1
./file2
./file.sign
./other.sign
./whileifs

I attached the test directory. Can you reproduce it ?

Sincerely
Y


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Re: dash & IFS

[Harald van Dijk]

On 23/03/2020 08:20, n8dandy wrote:
> Good morning,
> 
> Few days ago, I noticed something strange with dash and IFS. It was
> verified with the following versions :
> 
> - 0.5.10.2 on Voidlinux
> - 0.5.10.2 on Debian Buster
> - 0.5.8 on Ubuntu 18.04.2 LTS (Bionic Beaver)
> 
> Here the issue :
> 
> $ ls
> file.sign  file1  file2  other.sign  whileifs*
> $ cat whileifs
> #!/bin/dash
> 
> find . -type f | sort -d | while IFS=$'\n' read -r F; do
> 	printf "%s\n" "$F"
> done

This isn't about IFS, this is just because dash does not support the use 
of $'\n' to indicate a newline. In dash, $'\n' is equivalent to '$\n' 
(in the same way that x'y' is equivalent to 'xy' in all shells). To 
portably get a string consisting of a single newline, either put a 
literal newline in your source:

   nl='
   '

or use command substitutions:

   nl=$(printf '\n.'); nl=${nl%.}

Currently, $'...' is not part of POSIX (although it has been accepted 
for the next version), and dash tends not to add new features that are 
not part of the standard.

Cheers,
Harald van Dijk

Re: dash & IFS

[n8dandy]

On Monday, 23 March 2020 09:44, Harald van Dijk <harald@gigawatt.nl> wrote:

> On 23/03/2020 08:20, n8dandy wrote:
> This isn't about IFS, this is just because dash does not support the use
> of $'\n' to indicate a newline. In dash, $'\n' is equivalent to '$\n'
> (in the same way that x'y' is equivalent to 'xy' in all shells). To
> portably get a string consisting of a single newline, either put a
> literal newline in your source:
>
> nl='
> '
>
> or use command substitutions:
>
> nl=$(printf '\n.'); nl=${nl%.}
>
> Currently, $'...' is not part of POSIX (although it has been accepted
> for the next version), and dash tends not to add new features that are
> not part of the standard.

Thanks for your help. Even if $'...' is not POSIX, I thought dash already
supports it. I'll stick with IFS= instead.

Sincerely