java 用于反转字节顺序/更改字节序的命令行
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Command-line to reverse byte order/change endianess
提问by Alexander Torstling
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 a problem feeding the bytes to od. This is due to the fact that odalways assumes that the endianess matches the endianess of the arch that you are currently on, and I'm on a little endian machine.
我正在尝试解析一些由 Javas 编写的数据的脚本DataOutputStream#writeLong(...)。由于 java 似乎总是写大端，因此我在将字节提供给od. 这是因为od始终假设字节序与您当前所在的拱门的字节序相匹配，而我使用的是小型字节序机器。
I'm looking for an easy one-liner to reverse the byte order. Let's say that you know that the last 8 bytes of a file is a long written by the aforementioned writeLong(...)method. My current best attempt to print this long is
我正在寻找一种简单的单行来反转字节顺序。假设您知道文件的最后 8 个字节是由上述writeLong(...)方法写入的 long 。我目前打印这么长的最佳尝试是
tail -c 8 file | tac | od -t d8
, but taconly seems to work on text (fair enough). I've found some references to dd conv=swab, but this only swaps bytes in pairs, and cannot reverse these eight bytes.
，但tac似乎只适用于文本（足够公平）。我发现了一些对 的引用dd conv=swab，但这只是成对交换字节，不能反转这八个字节。
Does anyone know a good one-liner for this?
有没有人知道一个好的单线？
采纳答案by Alexander Torstling
Resorted to Perl in the end. Used a one-liner which I found at PERL One Liners:
最后求助于Perl。使用了我在PERL One Liners找到的单线：
tail -c 8 file | perl -0777e 'print scalar reverse <>' | od -t d8
The 0777separator char was a bit puzzling to me, but thispage at debian admin seems to suggest that it is a placeholder for 'no record separator', triggering a complete reverse byte-per byte.
该0777分离器字符是一个有点令人费解给我，但这个页面在Debian的管理员似乎表明，它是“无记录分隔符”占位符，引发了完整的反向字节每字节。
Other suggestions are welcome.
欢迎其他建议。
EDIT: Found another command in a comment to tac.c, which I downloaded from GNU coreutils:
编辑：在我从 GNU coreutils 下载的 tac.c 的评论中找到了另一个命令：
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
将每个 FILE 或标准输入（如果没有给出或遇到 FILE 名称“-”）复制到标准输出，记录顺序颠倒。记录由字符串的实例分隔，如果没有给出，则用换行符分隔。默认情况下，分隔符字符串附加到它在文件中跟随的记录的末尾。
选项：-b、--before 分隔符附加到文件中它前面的记录的开头。-r, --regex 分隔符是正则表达式。-s, --separator=separator 使用 SEPARATOR 作为记录分隔符。
要逐字节反转文件，请使用（在 bash、ksh 或 sh 中）： tac -r -s '.\| ' 文件
回答by Marc
You could use objcopy:
你可以使用objcopy：
$ objcopy -I binary -O binary --reverse-bytes=num inputfile.bin outputfile.bin
where num is either 2 or 4.
其中 num 是 2 或 4。
回答by pixelbeat
Note the next version of GNU coreutils (>= 8.23) will add the --endian={little,big} option to the od command
请注意下一版本的 GNU coreutils (>= 8.23) 将在 od 命令中添加 --endian={little,big} 选项
回答by Anton Chevychalov
Used dd, Luke!
用过 dd，卢克！
dd if=sourcefile of=resultfile conv=swab
回答by Brian Carcich
BASH:
巴什：
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).
为了根据 的输出样式更加健壮od，它可能需要压缩空格（在"| sed 's/ */ /g'"之后插入w8）。
回答by Mark Lakata
I came up with this Perl one-liner to convert 4-byte integers from one endianness to another:
我想出了这个 Perl one-liner 来将 4 字节整数从一个字节序转换为另一个字节序：
$ 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:
这可能在真正的 Linux 机器上运行良好，但 Cygwin 最后咬了我，将二进制文件视为文本并在每个 0x0A 字节（又名换行符）之前插入一个 0x0D（又名 CR）。但是，如果您使用管道cat -，它似乎就不管它了。这对我有用：
$ perl -e 'open F,shift; do { read(F,$a,4); print scalar reverse($a);} while(!eof(F));' bigend.bin | cat - > littlend.bin
