Byte operations

[Matesax]

Hi,
in BASH script I need to write (append) dword aligned string (that's stored in variable - UTF-8 - aligned by zero char) to one file. And also append two integer variables into this file - with word alignment. (word (2 bytes) + word = dword => I need dword (4 bytes) aligned record) How can I make this in easy way? (dword dword dword dword ... word word dword dword dword ... word word dword ...) (blab lah\0 0xA2B5 0xC4D8 lore m\ ip sum\0 0x1852 ...)
Thank you.

 

[ryanvade]

some form of awk I would think.

 

[Matesax]

OK - I have:

printf %.4x numberHere | xxd -r -p >> FileTable

BUT - how can I write in Little Endian - only manualy? (AA55 as 55AA)
($((43605 & 255)) and $((43605 >> 8)) looks very horrible)
Thank you.

OK - result:

writeInteger()
{
    printf %.4x $(((($1 & 255) << 8) | ($1 >> 8))) | xxd -r -p >> $temp/FileTable
}

...

    writeInteger $total
    writeInteger $count

    fileName=`basename $1`
    echo -n $fileName >> $temp/FileTable
    align=$((`echo -n $fileName | wc -c` % 4))

    if [ $align -gt 0 ]
    then
        truncate -s +$((4 - $align)) $temp/FileTable
    fi

It works, but I think, that it can be better...

Simple output:

06 00 04 00 65 64 69 74 2E 62 69 6E 0A 00 03 00 66 69 6C 65 6D 61 6E 2E 62 69 6E 00 0D 00 08 00 68 61 6E 67 6D 61 6E 2E 62 69 6E 00 15 00 02 00 6B 65 79 62 6F 61 72 64 2E 62 69 6E 17 00 02 00 6D 6F 6E 69 74 6F 72 2E 62 69 6E 00 19 00 01 00 73 65 72 69 61 6C 2E 62 69 6E 00 00 1A 00 02 00 76 69 65 77 65 72 2E 62 69 6E 00 00 1C 00 AA 03 74 65 73 74 2E 62 6D 70

 

[DevynCJohnson]

I do not know Perl, but it may offer better commands for this task.

 

[Matesax]

Yes!

writeIntegers()
{
    perl <<END
    open FS, '>>', "$temp/FileTable" or die "Unable to open: $!";
    print FS pack('v', $1), pack('v', $2);
    close FS;
END
}

...

perl <<END
    open FS, '+<', "$fs" or die "Unable to open: $!";
    seek FS, 689, 0;
    print FS pack('s<', $total), pack('s<', $count);
    close FS;
END