copying files with shell built in functions?

copying files with shell built in functions?

[Dominik Vogt]

In a fit of mental derangement, my colleagues tried to exchange
the libc on a machine at run time and used 'mv' to rename the
file.  As you might imagine, they regretted that immediately :-)

Can anyone think of a way to copy or rename a file with only shell
built in functions?  (either zsh or bash)  I have tried things
like

  $ while read <options> X; do echo <options> "$X"; done < ifile > ofile

and

  $ echo $(< ifile) > ofile

(does not work because echo destroys XR and LF)

or

  $ cat <<EOF > ofile
  $(< ifile)
  EOF

(does not work because it still needs a cat and the here document
is mangled.

Bye

Dominik ^_^  ^_^

RE: copying files with shell built in functions?

[Borzenkov Andrey]

> In a fit of mental derangement, my colleagues tried to exchange
> the libc on a machine at run time and used 'mv' to rename the
> file.  As you might imagine, they regretted that immediately :-)
> 
> Can anyone think of a way to copy or rename a file with only shell
> built in functions?  (either zsh or bash)  I have tried things
> like
> 
>   $ while read <options> X; do echo <options> "$X"; done < ifile > ofile
> 
> and
> 
>   $ echo $(< ifile) > ofile
> 
> (does not work because echo destroys XR and LF)
> 
> or
> 
>   $ cat <<EOF > ofile
>   $(< ifile)
>   EOF
> 
> (does not work because it still needs a cat and the here document
> is mangled.
> 

bor@itsrm2% zmodload zsh/files
bor@itsrm2% which mv
mv: shell built-in command
bor@itsrm2% which rm
rm: shell built-in command
bor@itsrm2% man zshmodules
bor@itsrm2% echo $ZSH_VERSION
4.0.4

-andrey

Re: copying files with shell built in functions?

[Stephane CHAZELAS]

On Fri, Mar 28, 2003 at 05:59:29PM +0100, Dominik Vogt wrote:
[...]
>   $ while read <options> X; do echo <options> "$X"; done < ifile > ofile
> 
> and
> 
>   $ echo $(< ifile) > ofile

bash can't handle '\0', so forget it.

If you have zsh 4, you probably have a mapfile module.

zmodload zsh/mapfile
print -rn -- $mapfile[ifile] > ofile

Also note the zsh/files modules which provides builtin
ln/mv/chown...

If you don't have modules (or can't load them anymore because
your libc is gone), you should still be able to do :

while IFS= read -r line; do
  print -r -- $line
done < ifile > ofile

You'll probably end-up with a trailing \n, but that shouldn't
harm.

But I'm surprises you don't have at least one statically linked
ln or mv somewhere.

Here, I have a statically linked /sbin/zsh with mapfile and
files built in. That can reveal useful.

Also note the "vared mapfile[somefile]" for a text editor.

-- 
Stéphane

Re: copying files with shell built in functions?

[Zefram]

Dominik Vogt wrote:
>In a fit of mental derangement, my colleagues tried to exchange
>the libc on a machine at run time and used 'mv' to rename the
>file.  As you might imagine, they regretted that immediately :-)

This is precisely what I created the zsh/files module for.  I have the
module loaded all the time, in normal user shells as well as root shells.
I've never had this kind of situation, where the external programs
were unusable, but I've frequently been glad that the argument length
limitations of exec(2) don't apply to builtins ("rm *" in a directory
with *lots* of files).

-zefram

Re: copying files with shell built in functions?

[Bart Schaefer]

On Mar 28,  6:00pm, Zefram wrote:
}
} Dominik Vogt wrote:
} >In a fit of mental derangement, my colleagues tried to exchange
} >the libc on a machine at run time and used 'mv' to rename the
} >file.  As you might imagine, they regretted that immediately :-)
} 
} This is precisely what I created the zsh/files module for.  I have the
} module loaded all the time, in normal user shells as well as root shells.

There's no "cp" in zsh/files, though.

Probably because

zsh% >newfile <oldfile

works just fine.

Re: copying files with shell built in functions?

[Stephane CHAZELAS]

On Fri, Mar 28, 2003 at 07:03:47PM +0000, Bart Schaefer wrote:
[...]
> There's no "cp" in zsh/files, though.
> 
> Probably because
> 
> zsh% >newfile <oldfile
> 
> works just fine.

But uses more or cat that generally don't work when there's no
libc.

-- 
Stéphane

Re: copying files with shell built in functions?

[Bart Schaefer]

On Mar 28,  8:11pm, Stephane CHAZELAS wrote:
} Subject: Re: copying files with shell built in functions?
}
} On Fri, Mar 28, 2003 at 07:03:47PM +0000, Bart Schaefer wrote:
} [...]
} > zsh% >newfile <oldfile
} > 
} > works just fine.
} 
} But uses more or cat that generally don't work when there's no
} libc.

True, I forgot about that.   (It is sort of silly when the multio code
already has a `while (read()) write()' loop.)  There's always:

zsh% print -nr -- "$(<oldfile)" >newfile

or (more fun, but not necessarily less memory intensive)

zsh% zmodload zsh/mapfile
zsh% mapfile[newfile]=$mapfile[oldfile]