linux shell提供md5sum用于计算校验MD5值。
md5sum - compute and check MD5 message digest
md5sum [OPTION]... [FILE]...
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 character indicating type (`*' for
binary, ` ' for text), and name for each FILE.
BUGS
The MD5 algorithm should not be used any more for security related purposes. Instead, better use an
SHA-2 algorithm, implemented in the programs sha224sum(1), sha256sum(1), sha384sum(1), sha512sum(1)
MD5算法不再推荐应用于安全领域，用SHA-2代替。linux同时提供了SHA相关命令。
SEE ALSO
The full documentation for md5sum is maintained as a Texinfo manual. If the info and md5sum programs
are properly installed at your site, the command
info coreutils 'md5sum invocation'
should give you access to the complete manual.
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一般应用，直接md5sum file
~$md5sum git-ssh.png
f5c4025ae3e854eb7dc10dc9f1689f67 git-ssh.png
~$md5sum git-ssh.png | cut -d ' ' -f 1
f5c4025ae3e854eb7dc10dc9f1689f67
~$sha256sum git-ssh.png
1450b09afe9df5818de7050d9d17b360afb6c0c4a71d04cd27e59f464e28fcf0 git-ssh.png