Hi,

I use the following code to extract an archive and a gzip from an
auto-extractible shell script.

#! /bin/sh

#-- extract binaries from $0
byte_val=`expr $FILEBYTE + 1`
tail +${byte_val}c ${CURRENTPWD}/${progname} >binaries.out 2>$NUL
[ $? -eq 0 -a -f binaries.out ] || { NO; EXIT
$BINARIES_EXTRACTION_FAILED; }

#-- extract archive for binaries.out
byte_val=`expr $GZIPBYTE + 1`
tail +${byte_val}c binaries.out >$tgzarchive 2>$NUL
[ $? -eq 0 -a -f "$tgzarchive" ] || { NO; EXIT
$BINARIES_EXTRACTION_FAILED; }

#-- extract gzip for binaries.out
head -c +$GZIPBYTE binaries.out >gzip 2>$NUL
[ $? -eq 0 -a -f gzip ] || { NO; EXIT $BINARIES_EXTRACTION_FAILED; }

The problem is that the script need to be portable on Linux and most of
Unix flavor (HP-UX, AIX, SCO, Solaris, UnixWare) and "head -c" is not
supported everywhere (not on SCO, UnixWare, Solaris).

Is it possible to reproduce the head -c behaviour with dd command (or
with another unix commands ?)

TIA and regards,

Geoffrey Kretz

igeeo76@gmail.com wrote:
> Hi,
>
> I use the following code to extract an archive and a gzip from an
> auto-extractible shell script.
>
> #! /bin/sh
>
> #-- extract binaries from $0
> byte_val=`expr $FILEBYTE + 1`
> tail +${byte_val}c ${CURRENTPWD}/${progname} >binaries.out 2>$NUL
> [ $? -eq 0 -a -f binaries.out ] || { NO; EXIT
> $BINARIES_EXTRACTION_FAILED; }
>
> #-- extract archive for binaries.out
> byte_val=`expr $GZIPBYTE + 1`
> tail +${byte_val}c binaries.out >$tgzarchive 2>$NUL
> [ $? -eq 0 -a -f "$tgzarchive" ] || { NO; EXIT
> $BINARIES_EXTRACTION_FAILED; }
>
> #-- extract gzip for binaries.out
> head -c +$GZIPBYTE binaries.out >gzip 2>$NUL
> [ $? -eq 0 -a -f gzip ] || { NO; EXIT $BINARIES_EXTRACTION_FAILED; }
>
> The problem is that the script need to be portable on Linux and most of
> Unix flavor (HP-UX, AIX, SCO, Solaris, UnixWare) and "head -c" is not
> supported everywhere (not on SCO, UnixWare, Solaris).
>
> Is it possible to reproduce the head -c behaviour with dd command (or
> with another unix commands ?)

Yes. Have you read tha man page of dd? (see "bs=..." and "count=...").

Janis

>
> TIA and regards,
>
> Geoffrey Kretz
>

On 5 Dec 2006 07:45:37 -0800, igeeo76@gmail.com
<igeeo76@gmail.com> wrote:
> Hi,
>
> I use the following code to extract an archive and a gzip from an
> auto-extractible shell script.
>
> #! /bin/sh
>
> #-- extract binaries from $0
> byte_val=`expr $FILEBYTE + 1`
> tail +${byte_val}c ${CURRENTPWD}/${progname} >binaries.out 2>$NUL
> [ $? -eq 0 -a -f binaries.out ] || { NO; EXIT
> $BINARIES_EXTRACTION_FAILED; }
>
> #-- extract archive for binaries.out
> byte_val=`expr $GZIPBYTE + 1`
> tail +${byte_val}c binaries.out >$tgzarchive 2>$NUL
> [ $? -eq 0 -a -f "$tgzarchive" ] || { NO; EXIT
> $BINARIES_EXTRACTION_FAILED; }
>
> #-- extract gzip for binaries.out
> head -c +$GZIPBYTE binaries.out >gzip 2>$NUL
> [ $? -eq 0 -a -f gzip ] || { NO; EXIT $BINARIES_EXTRACTION_FAILED; }
>
> The problem is that the script need to be portable on Linux and most of
> Unix flavor (HP-UX, AIX, SCO, Solaris, UnixWare) and "head -c" is not
> supported everywhere (not on SCO, UnixWare, Solaris).
>
> Is it possible to reproduce the head -c behaviour with dd command (or
> with another unix commands ?)
>
dd bs=$GZIPBYTE count=1 if=binaries.out of=gzip
For very large files you might need to make bs <= system RAM and
count=$((GZIPBYTE / bs))


--
When a girl marries she exchanges the attentions of many men for the
inattentions of one.
-- Helen Rowland

> dd bs=$GZIPBYTE count=1 if=binaries.out of=gzip
> For very large files you might need to make bs <= system RAM and
> count=$((GZIPBYTE / bs))
>
>
> --
> When a girl marries she exchanges the attentions of many men for the
> inattentions of one.
> -- Helen Rowland

Ok, thanks a lot. And as it doesn't use -skip, I guess that this
command is portable ?