Using the cmp Command (with examples)
The cmp command is a useful tool for comparing two files byte by byte. It can help identify differences between files and provide information about the first difference encountered. This article will explore different use cases of the cmp command and provide code examples to illustrate the functionality of each case.
Use Case 1: Output char and line number of the first difference between two files
The first use case involves comparing two files and outputting the character and line numbers of the first difference encountered. This can be achieved with the following command:
cmp path/to/file1 path/to/file2
Motivation: This use case is helpful when you need to quickly identify the location of the first difference between two files. By providing the character and line numbers, you can easily navigate to the specific location and investigate the discrepancy.
Explanation: The cmp command is followed by the paths to the two files that you want to compare. When executed, it will scan through the files byte by byte until a difference is found. Once a difference is detected, the command will output the character and line numbers where the difference occurred.
Example Output:
path/to/file1 path/to/file2 differ: char 102, line 3
In this example, the first difference between file1 and file2 was found at character 102 on line 3.
Use Case 2: Output info of the first difference: char, line number, bytes, and values
The second use case involves obtaining more detailed information about the first difference between two files, including the characters, line numbers, bytes, and their corresponding values. This can be achieved with the --print-bytes option:
cmp --print-bytes path/to/file1 path/to/file2
Motivation: Sometimes it is necessary to have a more comprehensive understanding of the differences between two files. By including information about the bytes and their values in the output, you can gain deeper insights into the discrepancies.
Explanation: In this use case, the --print-bytes option is added to the cmp command. By using this option, the command will not only output the character and line numbers of the first difference but also provide additional information about the bytes and their values at that location.
Example Output:
path/to/file1 path/to/file2 differ: char 102, line 3, byte 4, value 0xA2 (file1) != 0xFE (file2)
In this example, the first difference between file1 and file2 occurred at character 102 on line 3. The byte at that position had a value of 0xA2 in file1 and 0xFE in file2.
Use Case 3: Output the byte numbers and values of every difference
The third use case involves comparing two files and obtaining a complete overview of all the differences, including the byte numbers and their corresponding values. This can be achieved with the --verbose option:
cmp --verbose path/to/file1 path/to/file2
Motivation: When comparing large files or multiple files, it can be beneficial to have a complete report of all the differences. By including the byte numbers and values in the output, you can quickly identify patterns or recurring discrepancies.
Explanation: In this use case, the --verbose option is added to the cmp command. This option enables the command to output the byte numbers and values of every difference encountered between the two files.
Example Output:
46 0xA2 0xFE
81 0x10 0x18
104 0xC0 0x80
...
In this example, the output displays a list of byte numbers and their corresponding values that differ between file1 and file2. Each line represents a difference at a specific byte number, with the value in file1 on the left and the value in file2 on the right.
Use Case 4: Compare files but output nothing, yield only the exit status
The fourth use case involves comparing two files but suppressing any output from the cmp command, only returning the exit status. This can be achieved with the --quiet option:
cmp --quiet path/to/file1 path/to/file2
Motivation: Sometimes it is only necessary to determine whether two files are identical or different, without requiring any additional information about the differences. By using the --quiet option, you can obtain a simple yes or no answer.
Explanation: In this use case, the --quiet option is added to the cmp command. With this option, the command will compare the two files and return the exit status only. If the files are identical, the exit status will be 0. If there are differences, the exit status will be 1.
Example Output:
(exit status) 1
In this example, the exit status of the cmp command is 1, indicating that there are differences between file1 and file2.
Conclusion
The cmp command provides a simple and effective way to compare two files byte by byte. By utilizing different options, it offers several use cases that cater to different needs. Whether you require detailed information about the first difference or a simple confirmation of file equivalence, the cmp command is a versatile tool to have in your arsenal.
