Sha1sum

sha1sum is a computer program that calculates and verifies SHA-1 hashes. It is commonly used to verify the integrity of files. It (or a variant) is installed by default in most Unix-like operating systems. Variants include shasum (which permits SHA-1 through SHA-512 hash functions to be selected manually), sha224sum, sha256sum, sha384sum and sha512sum, which use a specific SHA-2 hash function, and sha3sum (which permits SHA-3 through SHA3-512, SHAKE, RawSHAKE and Keccak functions to be selected manually). Versions for Microsoft Windows also exist, and the ActivePerl distribution includes a perl implementation of shasum. On FreeBSD this utility is called sha512 and contains additional features.

The SHA-1 variants are proven vulnerable to collision attacks, and users should use for example a SHA-2 variant such as sha256sum instead to prevent tampering by an adversary.

It is included in GNU Core Utilities, Busybox and Toybox.

Several source code management systems, including Git, Mercurial, Monotone, and Fossil, use the sha1sum of various types of content (file content, directory trees, ancestry information, etc.) to uniquely identify them.

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