Shell learns 48 days----file checksum match

File Checksum Matching

If you suspect that there may be many files with the same Nevin , instead of comparing all ranks comparisons with cmp or diff , The amount of time that is spent will increase as the number of files increases to the sub-party .

This is possible with file checksum ( achieve approximately linear performance Span style= "Font-family:times New Roman". There are many tools available to calculate the checksum of a file and a string includes sum,cksum, checksum, message digest tool md5 md5sum, Security hashing algorithm tool sha,shalsum,sha256, sha384.

Case :

$echo-N "Hello" | md5sum | Cut-d '-f1

5d41402abc4b2a76b9719d911017c592

Parse : gets The MD5 of the string Hell .

md5sum: Show or check MD5 (128-bit) checksum , if no file option , or file is "-" is read from the standard input .

Echo-n: do not print line breaks

Cut:cut is used to cut columns or fields from a standard input or text file . Cut text to paste it into a text file .-D specify domain spaces and Tab key different field separators .-f1 represents the first domain .

The validator is used to generate a checksum key from the file and then use this check password to verify the integrity of the file . General documents can be distributed over the network with different locations . for a variety of reasons , data has the potential to lose several bits during the transfer process , resulting in file corruption .

So I need to use some test methods to determine if there are errors in the received file . we can verify the original file and the received file .

By comparing the results of both checks , It is possible to verify that the received file is correct . validation is important for writing backup scripts or system maintenance scripts .

verify with md5sum or shalsum

The most well-known and most widely used tests and techniques are md5sum and shalsum. they use the response algorithm for file content to generate validation results .

In order to calculate md5sum, use the following command :

$MD 5sum F1

42A6AB275D6AE3A62AB448FB44DFFB8A F1

Analysis : The resulting result is a three-character hexadecimal string followed by a file name .

Redirect the output checksum to a file , and then use this MD5 file to verify the integrity of the data :

Md5sum f1>f1. MD5

You can follow the following method to permanently vera the file when data integrity :

$MD 5sum-c F1.MD5

F1: OK

Analysis : If a determination is present , The document is undamaged .

Shalsum is another common test algorithm . he generates a length from the given input file + hexadecimal string of characters . its usage and md5sum very similar .

Multiple files can be verified

&md5sum F1 F2 > File.md5

$cat FILE.MD5

42A6AB275D6AE3A62AB448FB44DFFB8A F1

42a6ab275d6ae3a62ab448fb44dffb8a F2

Parse : The output will contain an inspection result string for a single file in each row .

You can verify data integrity with the generated files in the following ways :

$MD 5sum-c FILE.MD5

F1: OK

F2: OK

Analysis : This command outputs a message that the check results match

Verifying a directory

Validating a directory means that we need to evaluate all the files in the directory recursively .

He can use command md5deep or shaldeep to achieve . First , need to install Md5deep package ensures that these commands can be found . Use the following :

$MD 5DEEP-RL DIRECTORY_PATH>DIRECTORY.MD5

Analysis : the-r option represents the use of a recursive method , and the-l ( lowercase letter l) uses relative paths . output absolute path by default .

Use the following command to verify :

$MD 5sum-c DIRCETORY.MD5

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Shell learns 48 days----file checksum match