Copy a txt file to another text file in a defined position

I have two txt files. How to read a text in file 2 and then copy file 1 to file 2 under that text. Please help me. Thanks,

For example.

file 2:

hello

hi

How I copy file 1 to file 2 under the line "hello"?

Answer 1

[Walter Roberson]

If you are using windows, then

system('copy file2.txt+file1.txt file2.txt')

The + is magic to Windows copy.exe to tell copy to append all of the given sources together.

Note: when you use copy like this, copy will not necessarily automatically put in an end-of-line between file2.txt and file1.txt in the case that file2.txt does not end with end-of-line.

[Nam Nguyen]

Thanks alot, so if I need to copy file 1 to under a text in file 2. How can I do this?

For example.

File 2:

hello

hi

How I copy file 1 to file 2 under the line "hello"?

[Walter Roberson]

system('copy file2.txt+file1.txt file2.txt')

When you use the MS Windows copy.exe utility, then you can list a number of different sources (including files and devices) with + characters between them, and Windows will concatenate all of the sources together to write into the destination.

These days, the MATLAB alternative code would look like

writelines([readlines('file2.txt'); readlines('file1.txt')], 'file2.txt');

which would have the advantage of automatically adding a newline between the parts if file2.txt did not happen to end in a newline.

[Nam Nguyen]

Thanks Walter, so if I want to add file 1 to file 2 under the line "hello" in file 2. How do I modify this code.

[Walter Roberson]

Use readlines() on both files. Use startsWith or strcmp to search for the hello in the array for file2. Then form

[lines_for_file2(1:index_of_hello); lines_for_file1; lines_for_file2(index_of_hello+1:end)]

and writelines() that.

You might find that historically a lot of people assume that you can do the same task by using @doc:fopen() and loop fgetl on file2 until you find the key line, and then start fprintff or fwrite to write the lines for file1, with the assumption that doing so will somehow insert the lines for file1 inside of file2. That will not work.

In all systems since the day of Vax RMS (Record Management Services) from the early 1980s, text files are just continuous binary files with absolutely no overhead information about where to locate the lines. So if you start writing into the middle of an existing text file, you now always end up overwriting whatever is already there. There is absolutely no operating system support in the last 30 years for "inserting" text into the middle of a text file with the inserted text pushing the remaining data to later in the file. The only possibilities these days are to either rewrite the entire file, or else to do some careful buffering in memory in order to read ahead and store all of the data that will be overwritten by inserting the new text.