Possible Duplicate:
using bash: write bit representation of integer to file
I need to write the size of a file into a binary file. For example:
$ stat -c %s in.txt
68187
$ stat -c %s in.txt >> out.bin
Instead of writing 68187 as a string to out.bin, i want to write it as a 4 bytes integer to out.bin.
This is what I could come up with:
int=65534
printf "0: %.8x" $int | xxd -r -g0 >>file
Now depending on endianness you might want to swap the byte order:
printf "0: %.8x" $int | sed -E 's/0: (..)(..)(..)(..)/0: \4\3\2\1/' | xxd -r -g0 >>file
Example (decoded, so it's visible):
printf "0: %.8x" 65534 | sed -E 's/0: (..)(..)(..)(..)/0: \4\3\2\1/' | xxd -r -g0 | xxd
0000000: feff 0000 ....
This is for unsigned int, if the int is signed and the value is negative you have to compute the two's complement. Simple math.
printf "%.8x" 65534 | xxd -r -p
You can use the following function to convert a numeric VALUE into its corresponding character:
chr() {
printf \\$(printf '%03o' $1)
}
You have to convert the byte values individually, after each other in the correct order (endianess) for the machine/architecture that you use. So I guess, a little use of another scripting language that supports binary output would do the job best.
See if this works for you
perl -e "print pack('L',`stat -c %s in.txt`)">>out.bin
pack is quite versatile; if 'L' doesn't do what you want, see the documentation for various other formats. There's also a tutorial.