Merging files in linux

Linux merge command

On Unix-like operating systems, the merge command performs a three-way file merge.

The merge process analyzes three files: a base version, and two conflicting modified versions. It attempts to automatically combine both sets of modifications, based on the shared base version, into a single merged file. If automatic merge is not possible, it facilitates manual merging.

This page describes the GNU/Linux version of merge.

Description

merge is part of the RCS version control package. It is used to perform a three-way file merge.

merge analyzes three files — an original file, and two modified versions of the original — and compares them, line-by-line, attempting to resolve the differences between the two sets of modifications to create a single, unified file which represents both sets of changes.

Depending on the differences between the two sets of changes, this may be an automatic process or may require user input.

If neither set of changes conflicts with the other, merge can usually figure out what to do on its own. But if the two sets of changes conflict — for example, if the same line of text is worded differently in both modified files — merge shows the conflict in the resulting merged file.

How merging works

merge incorporates all changes that lead from file2 to file3 into file1. The result ordinarily goes into file1.

Suppose file2 is the original, and both file1 and file3 are modifications of file2. Then merge combines both changes.

A conflict occurs if both file1 and file3 have changes in a common segment of lines. If a conflict is found, merge normally outputs a warning and brackets the conflict with » >>>>>>» lines. For instance, a typical conflict looks like this:

If there are conflicts, the user should edit the result and delete one of the alternatives.

Syntax

Options

-A	Output conflicts using the -A style of diff3(1) (if supported by diff3). This merges all changes leading from file2 to file3 into file1, and generates the most verbose output.
-E, -e	These options specify conflict styles that generate less information than -A. See diff3(1) for details. The default is -E. With -e, merge does not warn about conflicts.
-L label	This option may be given up to three times, and specifies labels to be used in place of the corresponding file names in conflict reports. That is, merge -L x -L y -L z a b c generates output that looks like it came from files x, y, and z instead of from files a, b, and c.
-p	Send results to standard output instead of overwriting file1.
-q	Quiet mode. Do not warn about conflicts.
-V	Print RCS’s version number.

Examples

Let’s say we have a file named orig.txt with the following contents.

. and a file named mod1.txt, which is a modified version of orig.txt:

. and a file named mod2.txt, which is also a modified version of orig.txt:

. and we run merge as follows:

It analyzes all three files, write to mod1.txt, and display the following warning:

This means the merge was successful, but we should be aware that there was a conflict. If we open mod1.txt — which by default is the file where the merge is written — we find that it now contains the following text:

It is up to us to decide which «Oranges are. » line to keep (or to combine them in our own way), and make the edit to the file manually.

Related commands

diff — Identify the differences between two files.

Источник

how to merge multiple files into one single file in linux

Many a times you may have multiple files that needs to merged into one single file. It could be that you previously split a single file into multiple files, and want to just merge them back or you have several log files that you want merged into one. Whatever the reason, it is very easy to merge multiple text files into a single file in Linux.

The command in Linux to concatenate or merge multiple files into one file is called cat. The cat command by default will concatenate and print out multiple files to the standard output. You can redirect the standard output to a file using the ‘>‘ operator to save the output to disk or file system.

Another useful utility to merge files is called join that can join lines of two files based on common fields. It can however work only on two files at a time, and I have found it to be quite cumbersome to use. We will cover mostly the cat command in this post.

Merge Multiple files into One in Order

The cat command takes a list of file names as its argument. The order in which the file names are specified in the command line dictates the order in which the files are merged or combined. So, if you have several files named file1.txt, file2.txt, file3.txt etc…

bash$ cat file1.txt file2.txt file3.txt file4.txt > ./mergedfile.txt

The above command will append the contents of file2.txt to the end of file1.txt. The content of file3.txt is appended to the end of merged contents of file1.txt and file2.txt and so on…and the entire merged file is saved with the name mergedfile.txt in the current working directory.

Many a time, you might have an inordinately large number of files which makes it harder to type in all the file names. The cat command accepts regular expressions as input file names, which means you can use them to reduce the number of arguments.

bash$ cat file*.txt my*.txt > mergedfile.txt

This will merge all the files in the current directory that start with the name file and has a txt extension followed by the files that start with my and has a txt extension. You have to be careful about using regular expressions, if you want to preserve the order of files. If you get the regular expression wrong, it will affect the exact order in which the files are merged.

A quick and easy way to make sure the files get merged in the exact order you want, is to use the output of another file listing program such as ls or find and pipe it to the cat command. First execute the find command with the regular expression and verify the file order…

bash$ find . -name «file*.txt» -o -name «my*.txt»

This will print the files in order such that you can verify it to be correct or modify it to match what you want. You can then pipe that output into the cat command.

bash$ find . -name «file*.txt» -o -name «my*.txt» | xargs cat > ./mergedfile.txt

When you merge multiple files into one file using regular expressions to match them, especially when it is piped and where the output file is not very obvious, make sure that the regular expression does not match the filename of the merged file. In the case that it does match, usually the cat command is pretty good at error-ing out with the message “input file is output file”. But it helps to be careful to start with.

Merge Two Files at Arbitrary Location

Sometimes you might want to merge two files, but at a particular location within the content of a file. This is more like the process of inserting contents of one file into an another at a particular position in the file.

If the file sizes are small and manageable, then vi is a great editor tool to do this. Otherwise the option is to split the file first and then merge the resulting files in order. The easiest way is to split the file is based on the line numbers, exactly at where you want to insert the other file.

bash$ split -l 1234 file1.txt

You can split the file into any number of output files depending on your requirement. The above example will split the file file1.txt to chunks of 1234 lines. It is quite possible that you might end up with more than two files, named xaa, xab, xac etc..You can merge all of it back using the same cat command as mentioned earlier.

bash$ cat xaa file2.txt xa

The above command will merge the files in order with the contents of file2.txt in between the contents of xaa and xab.

Another use case is when you need to merge only specific parts of certain files depending on some condition. This is especially useful for me when I have to analyze several large log files, but am only interested in certain messages or lines. So, I will need to extract the important log messages based on some criteria from several log files and save them in a different file while also maintaining or preserving the order of the messages.

Though you can do this using cat and grep commands, you can do it with just the grep command as well.

bash$ grep -h «[Error]» logfile*.log > onlyerrors.log

The above will extract all the lines that match the pattern [Error] and save it to another file. You will have to make sure that the log files are in order when using the regular expression to match them, as mentioned earlier in the post.

Источник

Merging files in Linux

I am using Cygwin to merge multiple files. However, I wanted to know if my approach is correct or not. This is both a question and a discussion 🙂

First, a little info about the files I have:

1. Both the files have ASCII as well as NON ASCII Characters.
2. File1 has 7899097 lines in it and a size of

70.9 Mb
File2 has 14344391 lines in it and a size of

136.6 Mb

File Encoding Information:

This is the method I am following to merge the two files, sort them and then remove all the duplicate entries:

I create a temp folder and place both the text files inside it.

I run the following commands to merge both the files but keep a line break between the two

The resulting output.txt file has 22243490 lines in it and a size of 207.5 Mb

Now, if I run the sort command on it as shown below, I get an error since there are Non ASCII characters (maybe unicode, wide characters) present inside it:

So, I set the environment variable LC_ALL to C and then run the command as follows:

And, the result.txt has 22243488 lines in it and a size of 207.5 Mb.

So, result.txt is the same as output.txt

Now, I already know that there are many duplicate entries in output.txt, then why the above commands are not able to remove the duplicate entries?

Also, considering the large size of the files, I wanted to know if this is an efficient method to merge multiple files, sort them and then unique them?

Источник

How to Merge Multiple Files in Linux?

Let’s look at the different ways in which you can merge multiple files in Linux. We’ll majorly use the cat command for this purpose. So let us begin!

For the rest of this tutorial we will consider three files. Let’s create these files:

We’ll use the cat command to create these files, but you can also use the touch/nano command to create and edit the files.

Table of Contents

Displaying the content together

Since cat command is short for Concatenate, it is the first go to for concatenating the content together.

Note that the order in which the content appears is the order in which the files appear in the command. We can change the order in the command and verify.

Merge multiple files in Linux and store them in another file

To store the content that was displayed on the screen in the previous example, use the redirection operator. (>)

The output has been stored in a file. An important thing to note here is that cat command would create the file first if it doesn’t exist. The single redirection operator will overwrite the file rather than appending at the end. To append the content in the end consider the next example.

Appending content to an existing file

To append content after you merge multiple files in Linux to another file, use double redirection operator. (>>) along with cat command.

Rather than overwriting the contents of the file, this command appends the content at the end of the file. Ignoring such fine detail could lead to an unwanted blunder.

Using sed command to merge multiple files in Linux

Sed command, primarily used for performing text transformations and manipulation can also be used to merge files.

The content from the files is stored in the hold buffer temporarily, usually used to store a pattern. It is then written to the specified file.

Automating the process using For loop

For loop can save the effort of explicitly mentioning the file names. This will only work if the filenames follow a pattern. Like in our case the file names follow the pattern: file<1,2,3>.txt. This can be used to take advantage of for loop.

The code simply exploits the fact that the files are named in a similar pattern. This should motivate you to think about how you want to name your files going forward.

Conclusion

In this tutorial, we covered some of the ways to merge multiple files in Linux. The process of merging is not exclusive to text files. Other files such as logs, system reports can also be merged. Using For loop to merge files saves a lot of effort if the number of files to be merged is too large.

Источник