sha1sum – Compute & Check Secure Hash Algorithm Std 1 message digest.
sha1sum computes a 160-bit checksum/fingerprint/message-digest for each specified file. `sha1sum’ can also determine whether a file & checksum are consistent. The sums are computed as described in FIPS-180-1.
$ sha1sum file — Compute and print the MD5 checksum of that file.
$ sha1sum -c input.txt — Read checksum and filename from the file and validate checksums.
$ sha1sum -w -c input.txt — Same as above and warn if the checksums format is wrong in the file.
$ sha1sum –status -c input.txt — Indicate the status in exit status code.
Read: man sha1sum
Format of input.txt :