Dash only reads the first character from pipe (bash reads whole line)

Dash only reads the first character from pipe (bash reads whole line)

[Gioele Barabucci]

Hello,

a 6 year old Debian bug [1] describes a problem with reading from pipes 
that is still present in the current dash version (I tested up to git 
commit 7062c78).

The following test, by the original reporter, shows the problem

 > The 'read' command seems to only read the first character and not the 
 > whole line.
 >
 > Example / comparison with bash:
 >
 > # /bin/dash
 > # sudo modprobe nf_conntrack
 > # read MAX </proc/sys/net/netfilter/nf_conntrack_max
 > # echo $MAX
 > 2
 >
 > # /bin/bash
 > # read MAX </proc/sys/net/netfilter/nf_conntrack_max
 > # echo $MAX
 > 262144

It this a known problem? Are there workarounds?

Regards,

[1] https://bugs.debian.org/547902

--
Gioele Barabucci <gioele@svario.it>

Re: Dash only reads the first character from pipe (bash reads whole line)

[Herbert Xu]

Gioele Barabucci <gioele@svario.it> wrote:
> 
> > The 'read' command seems to only read the first character and not the 
> > whole line.
> >
> > Example / comparison with bash:
> >
> > # /bin/dash
> > # sudo modprobe nf_conntrack
> > # read MAX </proc/sys/net/netfilter/nf_conntrack_max
> > # echo $MAX
> > 2
> >
> > # /bin/bash
> > # read MAX </proc/sys/net/netfilter/nf_conntrack_max
> > # echo $MAX
> > 262144
> 
> It this a known problem? Are there workarounds?

Yes it's a known problem, but arguably it's more of a kernel bug
than a dash bug (proc files cannot be read byte-by-byte).  You
can work around it using cat

MAX=$(cat /proc/.../file)

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt