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 escapingThe 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 exitThe 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 LFMTThese format options provide fine-grained control over the outputof 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 LETTERLETTERs are as follows for new group, lower case for old group:F  first line numberL  last line numberN  number of lines = L-F+1E  F-1M  L+1%(A=B?T:E)  if A equals B then T else ELFMT (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 numberBoth GFMT and LFMT may contain:%%  %%c'C'  the single character C%c'\OOO'  the character with octal code OOOC    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 isa colon-separated list of terminfo capabilities--help               display this help and exit-v, --version            output version information and exitFILES 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。