源起

从国内的第三方网站下载了Android sutiod的zip包下载地址，为了安全起见还是得跟Android官网上的对应的zip包的SHA值做下对比。以前是经常使用md5命令的，所以理论在命令行下应该是有对应的命令行工具可以计算SHA值的。后来搜索到可以用 shasum命令来完成我的需求。
我们man一下shasum命令，注：需要注意-a参数，即计算文件散列值时可以选择具体的算法

SHASUM(1)                                                     Perl Programmers Reference Guide                                                     SHASUM(1)NAMEshasum - Print or Check SHA ChecksumsSYNOPSISUsage: shasum [OPTION]... [FILE]...Print or check SHA checksums.With no FILE, or when FILE is -, read standard input.-a, --algorithm   1 (default), 224, 256, 384, 512, 512224, 512256-b, --binary      read in binary mode-c, --check       read SHA sums from the FILEs and check them--tag         create a BSD-style checksum-t, --text        read in text mode (default)-U, --UNIVERSAL   read in Universal Newlines modeproduces same digest on Windows/Unix/Mac-0, --01          read in BITS modeASCII '0' interpreted as 0-bit,ASCII '1' interpreted as 1-bit,all other characters ignoredThe following five options are useful only when verifying checksums:--ignore-missing  don't fail or report status for missing files-q, --quiet           don't print OK for each successfully verified file-s, --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-h, --help        display this help and exit-v, --version     output version information and exitWhen verifying SHA-512/224 or SHA-512/256 checksums, indicate thealgorithm explicitly using the -a option, e.g.

实践

PS: sha256算法的散列值是256个byte，即256/8=32字节，1个字节用2位16制表示，即散列值的长度为64个字符
对比一下官网的信息，good，安全较验通过！

回顾

md5与sha256的区别

计算字符串长度

${#字符串变量}