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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。
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