I am appending a file in scala, and I want to replace the last line of the file with a new text. I know how to append to a file, but I can't figure out how to overwrite the last line.
I am appending like this:
val fw = new FileWriter("src/file.txt", true) ;
fw.write("new item");
Could anybody help?
The most efficient way I can think of is the following:
Read the file as a RandomAccessFile.
Go to the end of the file Start reading backwards till you find the
end of the last but one line.
Get rid of this last line
Append your line to this new file
Here is an example of how to remove the last line in Java using RandomAccessFile.
Delete last line in text file
Related
Im trying to get a code that will do something if a certain line number is in a text file for example "Test.txt"
Ex.
if line "x" exists in test.txt msg $chan working
thanks #denny for being the one to help me out.
if ($read(test.txt, n, x)) {
msg $chan working
}
You have couple of options.
Searching to see if the number is lower or equal to the total lines. e.g: $lines(filename)
You can extract the line and use a condition if it's full. e.g: $read(filename, LINE-NUMBER)
Notes for each method:
Will only tell you if there is a line number, NOT if there is something inside this line.
Will only give you the line if exists, if the line is empty or there is no such line then it will appears like it's empty.
I want to read and write the same file simultaneously. Here is a simplified code:
clc;
close all;
clearvars;
fd = fopen ('abcd.txt','r+'); %opening file abcd.txt given below
while ~feof(fd)
nline = fgetl(fd);
find1 = strfind(nline,'abcd'); %searching for matching string
chk1 = isempty(find1);
if(chk1==0)
write = '0000'; %in this case, matching pattern found
% then replace that line by 0000
fprintf(fd,'%s \n',write);
else
continue;
end
end
File abcd.txt
abcde
abcd23
abcd2
abcd355
abcd65
I want to find text abcd in string of each line and replace the entire line by 0000. However, there is no change in the text file abcd.txt. The program doesn't write anything in the text file.
Someone can say read each line and write a separate text file line by line. However, there is a problem in this approach. In the original problem, instead of finding matching text `abcd, there is array of string with thousands of elements. In that case, I want to read the file, parse the file for find matching string, replace string as per condition, go to next iteration to search next matching string and so on. So in this approach, line by line reading original file and simultaneously writing another file does not work.
Another approach can be reading the entire file in memory, replacing the string and iterate. But I am not very sure how will it work. Another issue is memory usage.
Any comments?
What you are attempting to do is not possible in a efficient way. Replacing abcde with 0000, which should be done for the first line, would require all remaining text forward because you remove one char.
Instead solve this reading one file and write to a second, then remove the original file and rename the new one.
I need to parse a CSV (well, more a tab delimited file) and create a new file that contains unique field - i.e.
RC100 1st line
RC100 2nd line
RC100 3rd line
RC200 1st line
and have in the new resultant file
RC100 1rd line
RC200 1st line
I was going to attempt this using VBScript then wondered if I can accomplish this using powershell (sort with -unique) but obviously didn't acheive success.
Please point me to the right direction.
Thanks.
Ray
How to give next line in row value if I have multiple value in one row and show in exporting csv file .
I want add text as new line this code is doing well, but I have multiple value in one row then it does not print that row, it only prints another row. How to solve this problem
buffer is string.
buffer = [buffer stringByAppendingFormat: #"\r\n%#", rowString];
"\n\n" should give you a new line.
I have a file full of ascii data. How would I append a string to the first line of the file? I cannot find that sort of functionality using fopen (it seems to only append at the end and nothing else.)
The following is a pure MATLAB solution:
% write first line
dlmwrite('output.txt', 'string 1st line', 'delimiter', '')
% append rest of file
dlmwrite('output.txt', fileread('input.txt'), '-append', 'delimiter', '')
% overwrite on original file
movefile('output.txt', 'input.txt')
Option 1:
I would suggest calling some system commands from within MATLAB. One possibility on Windows is to write your new line of text to its own file and then use the DOS for command to concatenate the two files. Here's what the call would look like in MATLAB:
!for %f in ("file1.txt", "file2.txt") do type "%f" >> "new.txt"
I used the ! (bang) operator to invoke the command from within MATLAB. The command above sequentially pipes the contents of "file1.txt" and "file2.txt" to the file "new.txt". Keep in mind that you will probably have to end the first file with a new line character to get things to append correctly.
Another alternative to the above command would be:
!for %f in ("file2.txt") do type "%f" >> "file1.txt"
which appends the contents of "file2.txt" to "file1.txt", resulting in "file1.txt" containing the concatenated text instead of creating a new file.
If you have your file names in strings, you can create the command as a string and use the SYSTEM command instead of the ! operator. For example:
a = 'file1.txt';
b = 'file2.txt';
system(['for %f in ("' b '") do type "%f" >> "' a '"']);
Option 2:
One MATLAB only solution, in addition to Amro's, is:
dlmwrite('file.txt',['first line' 13 10 fileread('file.txt')],'delimiter','');
This uses FILEREAD to read the text file contents into a string, concatenates the new line you want to add (along with the ASCII codes for a carriage return and a line feed/new line), then overwrites the original file using DLMWRITE.
I get the feeling Option #1 might perform faster than this pure MATLAB solution for huge text files, but I don't know that for sure. ;)
How about using the frewind(fid) function to take the pointer to the beginning of the file?
I had a similar requirement and tried frewind() followed by the necessary fprintf() statement.
But, warning: It will overwrite on whichever is the 1st line. Since in my case, I was the one writing the file, I put a dummy data at the starting of the file and then at the end, let that be overwritten after the operations specified above.
BTW, even I am facing one problem with this solution, that, depending on the length(/size) of the dummy data and actual data, the program either leaves part of the dummy data on the same line, or bring my new data to the 2nd line..
Any tip in this regards is highly appreciated.