击：写整数二进制文件 [英] Bash: write integer to binary file

问题描述

可能重复：结果
  <一href=\"http://stackoverflow.com/questions/2746707/using-bash-write-bit-re$p$psentation-of-integer-to-file\">using庆典：写位重新整数文件的presentation

Possible Duplicate:
using bash: write bit representation of integer to file

我需要一个文件的大小写入一个二进制文件。例如：

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

而不是写68187字符串out.bin的，我想写的168187在4个字节INT再presentation到out.bin。

Instead of writing "68187" string to out.bin, i want to write the 4 bytes int representation of 168187 to out.bin.

我如何转换68187至4个字节INT？

How can i convert "68187" to 4 bytes int?

推荐答案

这是我能想出的：

int=65534
printf "0: %.8x" $int | xxd -r -g0 >>file

现在根据字节序你可能希望交换的字节顺序：

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

示例（德codeD，所以它是可见的）：

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                                ....

这是对的符号的INT，如果int是的签名和的值的负的你要计算补。简单的数学。

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.

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