对于非常大的文件或者很重要的文件，在不稳定的网络环境下，可能文件的某些字节会损坏。此时，对文件计算MD5即可以校验其完整性。比如本次的 OpenStreetMap 导出包，我的学弟反馈通过网盘下载无法解压，并建议我增加每个文件的MD5校验。
对于文件非常多的情况，需要批量计算。最简便的方法是使用git自带的md5sum进行计算。
1. 安装git并进入bash
到 https://git-scm.com/ 下载git，并安装。
安装后，右键单击网盘下载的文件夹，选择“git bash” 进入bash:
可以查看 md5sum的说明
$ md5sum --help
Usage: md5sum [OPTION]... [FILE]...
Print or check MD5 (128-bit) checksums.
With no FILE, or when FILE is -, read standard input.
-b, --binary read in binary mode (default unless reading tty stdin)
-c, --check read MD5 sums from the FILEs and check them
--tag create a BSD-style checksum
-t, --text read in text mode (default if reading tty stdin)
-z, --zero end each output line with NUL, not newline,
and disable file name escaping
The following five options are useful only when verifying checksums:
--ignore-missing don't fail or report status for missing files
--quiet don't print OK for each successfully verified file
--status don't output anything, status code shows success
--strict exit non-zero for improperly formatted checksum lines
-w, --warn warn about improperly formatted checksum lines
--help display this help and exit
--version output version information and exit
The sums are computed as described in RFC 1321. When checking, the input
should be a former output of this program. The default mode is to print a
line with checksum, a space, a character indicating input mode ('*' for binary,
' ' for text or where binary is insignificant), and name for each FILE.
Note: There is no difference between binary mode and text mode on GNU systems.
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report any translation bugs to <https://translationproject.org/team/>
Full documentation <https://www.gnu.org/software/coreutils/md5sum>
or available locally via: info '(coreutils) md5sum invocation'
2. 批量计算md5
Linux常见命令 find 能够枚举文件并批量执行指令。
执行下面的指令，可以在屏幕输出各个文件的md5：
$ find ./Arch*.* -exec md5sum {} \;
d060dd81785d957ae4e2bbd4f9ebeb4e *./ArchOSManjaro.7z.001
b7326e73452d3fbbc56a889f55aa9a14 *./ArchOSManjaro.7z.002
805c9ef68887953554c6c160c2a72eeb *./ArchOSManjaro.7z.003
#...
2cc5ab567abba1d7e3a284ec5c383d84 *./ArchOSManjaro.7z.059
$
执行下面的指令，可以在文件输出各个文件的md5：
$ find ./Arch*.* -exec md5sum {} >> md5.txt \;
3.比较两个文件是否一致
我们假设本地校验结果放在check.txt，标准校验结果放在 md5.txt，则使用下面指令比较：
$ diff --help
Usage: diff [OPTION]... FILES
Compare FILES line by line.
Mandatory arguments to long options are mandatory for short options too.
--normal output a normal diff (the default)
-q, --brief report only when files differ
-s, --report-identical-files report when two files are the same
-c, -C NUM, --context[=NUM] output NUM (default 3) lines of copied context
-u, -U NUM, --unified[=NUM] output NUM (default 3) lines of unified context
-e, --ed output an ed script
-n, --rcs output an RCS format diff
-y, --side-by-side output in two columns
-W, --width=NUM output at most NUM (default 130) print columns
--left-column output only the left column of common lines
--suppress-common-lines do not output common lines
-p, --show-c-function show which C function each change is in
-F, --show-function-line=RE show the most recent line matching RE
--label LABEL use LABEL instead of file name and timestamp
(can be repeated)
-t, --expand-tabs expand tabs to spaces in output
-T, --initial-tab make tabs line up by prepending a tab
--tabsize=NUM tab stops every NUM (default 8) print columns
--suppress-blank-empty suppress space or tab before empty output lines
-l, --paginate pass output through 'pr' to paginate it
-r, --recursive recursively compare any subdirectories found
--no-dereference don't follow symbolic links
-N, --new-file treat absent files as empty
--unidirectional-new-file treat absent first files as empty
--ignore-file-name-case ignore case when comparing file names
--no-ignore-file-name-case consider case when comparing file names
-x, --exclude=PAT exclude files that match PAT
-X, --exclude-from=FILE exclude files that match any pattern in FILE
-S, --starting-file=FILE start with FILE when comparing directories
--from-file=FILE1 compare FILE1 to all operands;
FILE1 can be a directory
--to-file=FILE2 compare all operands to FILE2;
FILE2 can be a directory
-i, --ignore-case ignore case differences in file contents
-E, --ignore-tab-expansion ignore changes due to tab expansion
-Z, --ignore-trailing-space ignore white space at line end
-b, --ignore-space-change ignore changes in the amount of white space
-w, --ignore-all-space ignore all white space
-B, --ignore-blank-lines ignore changes where lines are all blank
-I, --ignore-matching-lines=RE ignore changes where all lines match RE
-a, --text treat all files as text
--strip-trailing-cr strip trailing carriage return on input
--binary read and write data in binary mode
-D, --ifdef=NAME output merged file with '#ifdef NAME' diffs
--GTYPE-group-format=GFMT format GTYPE input groups with GFMT
--line-format=LFMT format all input lines with LFMT
--LTYPE-line-format=LFMT format LTYPE input lines with LFMT
These format options provide fine-grained control over the output
of diff, generalizing -D/--ifdef.
LTYPE is 'old', 'new', or 'unchanged'. GTYPE is LTYPE or 'changed'.
GFMT (only) may contain:
%< lines from FILE1
%> lines from FILE2
%= lines common to FILE1 and FILE2
%[-][WIDTH][.[PREC]]{doxX}LETTER printf-style spec for LETTER
LETTERs are as follows for new group, lower case for old group:
F first line number
L last line number
N number of lines = L-F+1
E F-1
M L+1
%(A=B?T:E) if A equals B then T else E
LFMT (only) may contain:
%L contents of line
%l contents of line, excluding any trailing newline
%[-][WIDTH][.[PREC]]{doxX}n printf-style spec for input line number
Both GFMT and LFMT may contain:
%% %
%c'C' the single character C
%c'\OOO' the character with octal code OOO
C the character C (other characters represent themselves)
-d, --minimal try hard to find a smaller set of changes
--horizon-lines=NUM keep NUM lines of the common prefix and suffix
--speed-large-files assume large files and many scattered small changes
--color[=WHEN] color output; WHEN is 'never', 'always', or 'auto';
plain --color means --color='auto'
--palette=PALETTE the colors to use when --color is active; PALETTE is
a colon-separated list of terminfo capabilities
--help display this help and exit
-v, --version output version information and exit
FILES are 'FILE1 FILE2' or 'DIR1 DIR2' or 'DIR FILE' or 'FILE DIR'.
If --from-file or --to-file is given, there are no restrictions on FILE(s).
If a FILE is '-', read standard input.
Exit status is 0 if inputs are the same, 1 if different, 2 if trouble.
Report bugs to: bug-diffutils@gnu.org
GNU diffutils home page: <https://www.gnu.org/software/diffutils/>
General help using GNU software: <https://www.gnu.org/gethelp/>
执行指令：
$ diff check.txt md5.txt
36c36
< 23dfa036cd5d772f01173da67ebf2634 *./ArchOSManjaro.7z.029
---
> db2ce0bc5c39fd5d8f672f478788095c *./ArchOSManjaro.7z.029
可以看到第29号文件有问题。
使用 -y 选项，可以查看完整输出（左右两列）
$ diff -y check.txt md5.txt
..
e155774f7dd158ded02d9a9aae68f5eb *./ArchOSManjaro.7z.028 e155774f7dd158ded02d9a9aae68f5eb *./ArchOSManjaro.7z.028
23dfa036cd5d772f01173da67ebf2634 *./ArchOSManjaro.7z.029 | db2ce0bc5c39fd5d8f672f478788095c *./ArchOSManjaro.7z.029
c8c32363ebd14a7eefce1cadaaa64def *./ArchOSManjaro.7z.030 c8c32363ebd14a7eefce1cadaaa64def *./ArchOSManjaro.7z.030
...
不一致的行，会用竖线“|”标记。
