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This article mainly introduces the Linux system diff command how to use, the article is very detailed, has a certain reference value, interested friends must read it!

In the Linux system, the diff command is mainly used to compare file differences, and the differences between files can be printed after the command is executed. It can compare the contents of two files line by line, or recursively compare the contents of a folder.

Syntax diff [- abBcdefHilnNpPqrstTuvwy] [-] [- C] [- D] [- I] [- S] [- W] [- x] [- X] [--help] [--left-column] [--suppress-common-line] [file or directory 1] [file or directory 2] parameter:-specifies how many lines of text to display. This parameter must be used with the-c or-u parameter.

The-an or-text diff preset only compares text files line by line.

-b or-ignore-space-change do not check for differences in space characters.

-B or-ignore-blank-lines does not check for blank lines.

-c shows all the text and marks the differences.

-C or-context is the same as executing the "- c -" instruction.

-d or-minimal use different algorithms to make comparisons in smaller units.

-D or ifdef the output format of this parameter can be used for preprocessor macros.

The output format of-e or-ed of this parameter can be used in the script file of ed.

The format of the-f or-forward-ed output is similar to ed's script file, but the differences are shown in the order of the original file.

-H or-speed-large-files can speed up when you compare large files.

-l or-ignore-matching-lines if the two files are different on certain lines, and both lines contain the characters or strings specified in the option, the difference between the two files is not displayed.

-I or-ignore-case do not check for case differences.

Either-l or-paginate passes the results to the pr program for paging.

-n or-rcs will display the comparison results in RCS format.

When comparing directories with-N or-new-file, if file An appears only in a directory, the preset will display:

Only in directory: if file A uses the-N parameter, diff compares file A with a blank file.

-p if the compared file is a C language program code file, the name of the function where the difference is located is displayed.

-P or-unidirectional-new-file is similar to-N, but only if the second directory contains a file that is not available in the first directory will this file be compared to a blank file.

-Q or-brief only shows whether there is a difference, not detailed information.

-r or-recursive compare files in a subdirectory.

If no difference is found in-s or-report-identical-files, the message is still displayed.

When comparing directories,-S or-starting-file starts the comparison from the specified file.

-t or-expand-tabs expands the tab character on output.

-T or-initial-tab precede each line with a tab character for alignment.

-UMAL or-unified= show differences in the contents of the file in a merged way.

-v or-version displays version information.

-w or-ignore-all-space ignores all space characters.

-W or-width specifies the column width when using the-y parameter.

-x or-exclude do not compare the files or directories specified in the options.

-X or-exclude-from you can save the file or directory type as a text file, and then specify this text file in =.

-y or-side-by-side shows the similarities and differences of the file in a side-by-side manner.

-help displays help.

When-left-column uses the-y parameter, if one line of the two files is the same, it only displays that line in the field on the left.

-suppress-common-lines shows only the difference when using the-y parameter.

Case demonstration: suppose we have two files (file1 and file2):

$cat file1 Hi, Hello, How are you? I am fine, Thank you. $cat file2 Hello, Hi, How are you? I am fine. You can see that there is a slight difference between the two files. Now, let's see how the diff command can find out the difference between the two.

Run the diff command like this:

$diff file1 file2 1d0 Hi, 4pm 5c4 I am fine. You can see that diff is followed by the names of two files as command line arguments, and it generates a difference comparison in the output. The output is not easy to understand. The reason is that it is used by computers, not for humans. However, let's decode the output step by step:

Note-in the following text, file1 and file2 will be treated as old and new files.

1d0 here, the line 1d0 means that the first line of the old file should be deleted (d) to synchronize the first line of the two files. The line that needs to be deleted in the old file is' 2a2 > Hi, where the 2a2 line means that the second line in the new file should be added to the second line in the old file. The line to be added is displayed on the next line of the output marked with'>'. 4,5c4 I am fine. Here, the line 4jre 5c4 means that the 4 to 5 lines in the old file have now been changed and need to be replaced by the fourth line in the new file. Add and delete lines with'> 'and' so, to sum up, the first parameter of the diff command is treated as an old file and the second parameter is treated as a new file.

Expressions such as 1d0, 2a2, 4jade 5c4 can be syntactically decoded to the line number or line range of the old file [the line number or line range of the new file]. The 'behavior' here can be appended, deleted, or changed to replace.

'' represents the added row.

In addition to files, the diff command can also compare two directories. Let's learn through an example.

Here is the contents of the 'new_dir' directory:

$ls new_dir/ file file2 frnd frnd1.cpp log1.txt log3.txt log5.txt file1 file name with spaces frnd1 frnd.cpp log2.txt log4.txt this is what the 'origdir'' directory contains: (translation note: the original text is and here are the contents of a directory named 'olddir', where' old_dir' should be a clerical error.)

The following is the output after the execution of the diff command: $ls orig_dir/ file1 file name with spaces frnd1 frnd.cpp log2.txt log4.txt test file2 frnd frnd1.cpp log1.txt log3.txt log5.txt

Diff new_dir/ orig_dir/ Only in new_dir/: file Only in orig_dir/: test you can see that when the diff command is used to compare the two directories, it is easy to display the missing files in the two files.

Here are some options commonly used on the command line:

1. Ignore case with-I if two files contain the same text but different case, the diff command still reports that it is different by default.

For example:

$cat file1 HI $cat file2 hi $diff file1 file2 1c1 hi you can see that the diff command reports a case difference in the output.

To remove this default behavior, use the-I option.

Here is an example:

$diff-I file1 file2 $so you can see that no output is generated, which is the default behavior when two files are the same.

two。 Using the-s option to report that two files are the same later in example 1, we see that diff will not generate a report if the files are the same. Although this default behavior is good, it can still cause a lot of confusion, especially for beginners. So, if you have a decent diff command that explicitly reports that the two files are different, use the-s command option.

Let's give an example:

$diff-is file1 file2 Files file1 and file2 are identical you can see that I added the-s option in the later example, this time the diff command will explicitly report that the two files are the same.

3. Another common way to ignore spaces with-b is that the diff report file has a different number of spaces.

Examples are as follows:

$cat file1 Hi, how are you? $cat file2 Hi, how are you? The only difference between the two files is the extra space between 'are'' and 'you'' in file2. Now, when you use the diff command to compare two files, the output is as follows:

$diff file1 file2 1c1 Hi, how are you? So you can see that the diff command reports a difference. But if you want to ignore these spaces, use the-b option.

$diff-b file1 file2 $so you can see that due to the-b option, the diff command reports that the two files are the same.

The diff command also provides more command-line options. Read man page for a complete list.

The above is all the contents of this article entitled "how to use diff commands in Linux system". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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