write to first line of CSV/TXT file problem

speedamp

Hi everybody,

I have been searching around everywhere on an efficient way to edit ONLY the first line of a csv/txt file.

can you somebody help me find a good way to do this:

read the lines something like this:
$lines = file($csvfile);

and then all I want to do is append a comma to the end of the first line and and rewrite it (without wiping out the entire file).

$new_line = $lines[0].","; // this new line shoudl simply replace the first line in the file but i can't get this to work.

thanks!

-Michael

NogDog

$lines = file($csvfile);
$lines[0] .= ',';
$fh = fopen($csvfile, 'w');
fwrite($fh, implode('', $lines));

etully

First of all, I think you meant to implode $lines, right?. Second of all, I think the OP was looking for a more efficient way of doing it where it only writes one line back to the hard drive. (Imagine if this was a 5GB log file, the reads/writes would kill you). And for that, I don't think there is a solution except to use a database instead of a text file.

NogDog

etully wrote:
First of all, I think you meant to implode $lines, right?.

Code has been edited accordingly. Thanks.

etully wrote:
Second of all, I think the OP was looking for a more efficient way of doing it where it only writes one line back to the hard drive. (Imagine if this was a 5GB log file, the reads/writes would kill you). And for that, I don't think there is a solution except to use a database instead of a text file.

Maybe, and then again maybe it's a 1KB file and the whole purpose of that code is to fix a CSV formatting error created by some other application that he has no control over. I was just answering the question, which was requesting "an efficient way to edit ONLY the first line of a csv/txt file." Maybe it's not subjectively "efficient", depending on how you want to define efficient, but it's the least inefficient way I know to answer the question as posed here. I was not suggesting how I would redesign the entire application, particularly since I know nothing about what he is trying to do and what the functional requirements are that he is trying to satisfy.

Sometimes good-enough solutions are good enough. Then again, sometimes you need to re-factor when you find it does not scale.

etully

Wait, No criticism was meant NogDog - I wasn't challenging your solution - it's very tight. All I meant was that I think the OP was looking for a way to edit exactly one line in a file without having to read in all the lines and then write out all the lines. (Especially in this situation, he's only changing one byte.)

I have sometimes wished I could say:

fopen
fread line 56
alter string
fwrite line 56
fclose

That would be efficient from an I/O perspective - especially on a very large file. But instead, as far as I know, the only way to edit one line in a text file from PHP is to read in all the lines, make the change, and then write out all the lines.

NogDog

I remember reading somewhere that there's a way to do that if the file is of fixed-length records (i.e., every line is the same length) using some stream functions or such, but I'm (obviously) unsure as to the details, and of course it would not apply to this situation.