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sha256sum:tldr:401d6
The command sha256sum --check --quiet ${filename-sha256}
is used to perform a quick check on the integrity of one or more files using the SHA-256 hash algorithm.
Here's a breakdown of each component of the command:
-
sha256sum
: This is the command used to calculate the SHA-256 hash values of files. It generates a unique 256-bit hash value for each file passed to it. -
--check
: This flag tells thesha256sum
command to read a list of SHA-256 hashes and filenames from a file (or from standard input) and check if the calculated hash of each file matches the provided hash. -
--quiet
: This flag tells thesha256sum
command to not display any output for files whose hash matches the provided hash. It only displays output for files that do not match the hash. -
${filename-sha256}
: This is a parameter expansion or substitution that is used to specify the file containing the list of SHA-256 hashes and filenames. The actual name of the file is represented byfilename
here. The-sha256
part suggests that the file is named with the.sha256
extension.
So, when you execute this command, it reads a file (specified by ${filename-sha256}
) which contains a list of filenames and corresponding SHA-256 hashes. It then calculates the SHA-256 hash of each file in the list and compares it with the provided hash. If the hashes match, it remains silent (due to --quiet
) and doesn't display any output. If the hashes don't match, it displays an error message indicating that the file has been modified or corrupted.