Command-line to reverse byte order/change endianess

Question

I\'m hacking around in some scripts trying to parse some data written by Javas DataOutputStream#writeLong(...). Since java always seems to write big endian, I have

Answer 1

Resorted to Perl in the end. Used a one-liner which I found at PERL One Liners:

tail -c 8 file | perl -0777e 'print scalar reverse <>' | od -t d8

The 0777 separator char was a bit puzzling to me, but this page at debian admin seems to suggest that it is a placeholder for 'no record separator', triggering a complete reverse byte-per byte.

Other suggestions are welcome.

EDIT: Found another command in a comment to tac.c, which I downloaded from GNU coreutils:

Copy each FILE, or the standard input if none are given or when a FILE name of "-" is encountered, to the standard output with the order of the records reversed. The records are separated by instances of a string, or a newline if none is given. By default, the separator string is attached to the end of the record that it follows in the file.

Options: -b, --before The separator is attached to the beginning of the record that it precedes in the file. -r, --regex The separator is a regular expression. -s, --separator=separator Use SEPARATOR as the record separator.

To reverse a file byte by byte, use (in bash, ksh, or sh): tac -r -s '.\| ' file

Answer 2

Used dd, Luke!

dd if=sourcefile of=resultfile conv=swab

Answer 3

I came up with this Perl one-liner to convert 4-byte integers from one endianness to another:

$ perl -e 'open F,shift; do { read(F,$a,4); print scalar reverse($a);} while(!eof(F));' bigend.bin > littlend.bin

That probably works fine on real Linux machines, but Cygwin bit me in the end, treating the binary file as text and inserting a 0x0D (aka CR) before each 0x0A byte (aka newline). But if you pipe to cat -, it seems to leave it alone. This works for me:

$ perl -e 'open F,shift; do { read(F,$a,4); print scalar reverse($a);} while(!eof(F));' bigend.bin | cat - > littlend.bin

Answer 4

You could use objcopy:

$ objcopy -I binary -O binary --reverse-bytes=num inputfile.bin outputfile.bin

where num is either 2 or 4.

Answer 5

BASH:

od -b -v -w8 | while read pfx b8 ; do [ "$b8" ] && echo -n 12345678 | tr 87654321 \\${b8// /\\} ; done

To be a bit more robust depending on the output style of od, it may need to compress spaces ( insert "| sed 's/ */ /g'" after the w8).

Answer 6

Note the next version of GNU coreutils (>= 8.23) will add the --endian={little,big} option to the od command