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GNU Core-utils

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6.4 md5sum: Print or check message-digests

md5sum computes a 128-bit checksum (or fingerprint or message-digest) for each specified file. If a file is specified as `-' or if no files are given md5sum computes the checksum for the standard input. md5sum can also determine whether a file and checksum are consistent. Synopses:

 
md5sum [option]... [file]...
md5sum [option]... --check [file]

For each file, `md5sum' outputs the MD5 checksum, a flag indicating a binary or text input file, and the filename. If file is omitted or specified as `-', standard input is read.

The program accepts the following options. Also see 2. Common options.

`-b'
`--binary'
Treat all input files as binary. This option has no effect on Unix systems, since they don't distinguish between binary and text files. This option is useful on systems that have different internal and external character representations. On MS-DOS and MS-Windows, this is the default.

`-c'
`--check'
Read filenames and checksum information from the single file (or from stdin if no file was specified) and report whether each named file and the corresponding checksum data are consistent. The input to this mode of md5sum is usually the output of a prior, checksum-generating run of `md5sum'. Each valid line of input consists of an MD5 checksum, a binary/text flag, and then a filename. Binary files are marked with `*', text with ` '. For each such line, md5sum reads the named file and computes its MD5 checksum. Then, if the computed message digest does not match the one on the line with the filename, the file is noted as having failed the test. Otherwise, the file passes the test. By default, for each valid line, one line is written to standard output indicating whether the named file passed the test. After all checks have been performed, if there were any failures, a warning is issued to standard error. Use the `--status' option to inhibit that output. If any listed file cannot be opened or read, if any valid line has an MD5 checksum inconsistent with the associated file, or if no valid line is found, md5sum exits with nonzero status. Otherwise, it exits successfully.

`--status'
This option is useful only when verifying checksums. When verifying checksums, don't generate the default one-line-per-file diagnostic and don't output the warning summarizing any failures. Failures to open or read a file still evoke individual diagnostics to standard error. If all listed files are readable and are consistent with the associated MD5 checksums, exit successfully. Otherwise exit with a status code indicating there was a failure.

`-t'
`--text'
Treat all input files as text files. This is the reverse of `--binary'.

`-w'
`--warn'
When verifying checksums, warn about improperly formatted MD5 checksum lines. This option is useful only if all but a few lines in the checked input are valid.


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