How to place a file pointer in the choosen line (e.g. 1 lime from the bottom) when opening file with fopen()?
If you know the offset within the file of the data you want you could always fseek () to it. Of course the problem is discovering where you need to fseek to within the file. If you can use SEEK_END as an option then the offset will be relative to the end of the file instead of the beginning, which may be helpful for you.
Alternatively, you could use the file () function to load the file data into an array. Each element on the array represents a line of the file, so the second to last element in the array will be the item you want.
You will probably have to read your file counting line endings "\n". Something like:
function fseek_line($handle, $count) {
while ((--$count > 0) && (fgets($handle, 4096) !== false)) { }
}
If you need the last line just open in append mode fopen("file.txt", "a");
There is a SplFileObject::seek method that can position the pointer to Nth line.
Unfortunatly there is no easy way for this. Since files are not stored linewise there is no order to jump one line or several.
But check out this thread: fseek() by line, not bytes?
Related
What is the best way to overwrite a specific line in a file? I basically want to search a file for the string '#parsethis' and overwrite the rest of that line with something else.
If the file is really big (log files or something like this) and you are willing to sacrifice speed for memory consumption you could open two files and essentially do the trick Jeremy Ruten proposed by using files instead of system memory.
$source='in.txt';
$target='out.txt';
// copy operation
$sh=fopen($source, 'r');
$th=fopen($target, 'w');
while (!feof($sh)) {
$line=fgets($sh);
if (strpos($line, '#parsethis')!==false) {
$line='new line to be inserted' . PHP_EOL;
}
fwrite($th, $line);
}
fclose($sh);
fclose($th);
// delete old source file
unlink($source);
// rename target file to source file
rename($target, $source);
If the file isn't too big, the best way would probably be to read the file into an array of lines with file(), search through the array of lines for your string and edit that line, then implode() the array back together and fwrite() it back to the file.
Your main problem is the fact that the new line may not be the same length as the old line. If you need to change the length of the line, there is no way out of rewriting at least all of the file after the changed line. The easiest way is to create a new, modified file and then move it over the original. This way there is a complete file available at all times for readers. Use locking to make sure that only one script is modifying the file at once, and since you are going to replace the file, do the locking on a different file. Check out flock().
If you are certain that the new line will be the same length as the old line, you can open the file in read/write mode (use r+ as the second argument to fopen()) and call ftell() to save the position the line starts at each time before you call fgets() to read a line. Once you find the line that you want to overwrite, you can use fseek() to go back to the beginning of the line and fwrite() the new data. One way to force the line to always be the same length is to space pad it out to the maximum possible length.
This is a solution that works for rewriting only one line of a file in place with sed from PHP. My file contains only style vars and is formatted:
$styleVarName: styleVarProperty;\n
For this I first add the ":" to the ends of myStyleVarName, and sed replaces the rest of that line with the new property and adds a semicolon.
Make sure characters are properly escaped in myStyleVarProp.
$command = "pathToShellScript folder1Name folder2Name myStyleVarName myStyleVarProp";
shell_exec($command);
/* shellScript */
#!/bin/bash
file=/var/www/vhosts/mydomain.com/$1/$2/scss/_variables.scss
str=$3"$4"
sed -i "s/^$3.*/$str;/" $file
or if your file isn't too big:
$sample = file_get_contents('sample');
$parsed =preg_replace('##parsethis.*#', 'REPLACE TO END OF LINE', $sample);
You'll have to choose delimiters '#' that aren't present in the file though.
If you want to completely replace the contents of one file with the contents of another file you can use this:
rename("./some_path/data.txt", "./some_path/data_backup.txt");
rename("./some_path/new_data.txt", "./some_path/data.txt");
So in the first line you backup the file and in the second line you replace the file with the contents of a new file.
As far as I can tell the rename returns a boolean. True if the rename is successful and false if it fails. One could, therefore, only run the second step if the first step is successful to prevent overwriting the file unless a backup has been made successfully. Check out:
https://www.php.net/manual/en/function.rename.php
Hope that is useful to someone.
Cheers
Adrian
I'd most likely do what Jeremy suggested, but just for an alternate way to do it here is another solution. This has not been tested or used and is for *nix systems.
$cmd = "grep '#parsethis' " . $filename;
$output = system($cmd, $result);
$lines = explode("\n", $result);
// Read the entire file as a string
// Do a str_repalce for each item in $lines with ""
I'm trying to open a file and determine if it is valid. It's valid if the first line is START and the last line is END.
I've seen different ways of getting the last line of a file, but it does not pay particular attention to the first line either.
How should I go about this? I was thinking of loading the file contents in an array and checking $array[0] and $array[x] for START and END. But this seems to be a waste for all the junk that could possibly be in the middle.
If its a valid file, I will be reading/processing the contents of the file between START and END.
Don't read entire file into an array if it is not needed. If file can be big you can do it that way:
$h = fopen('text.txt', 'r');
$firstLine = fgets($h);
fseek($h, -3, SEEK_END);
$lastThreeChars = fgets($h);
Memory footprint is much lower
That's from me:
$lines = file($pathToFile);
if ($lines[0] == 'START' && end($lines) == 'END') {
// do stuff
}
Reading whole file with fgets will be efficient for small siles. iF ur file is big then:
open It and read first line
use tail (i didn't check it but it looks OK) function I found in php.net in fseek documentation
I want to make a .php file downloadable by my users.
Every file is different from an user to another:
at the line #20 I define a variable equal to the user ID.
To do so I tried this: Copy the original file. Read it until line 19 (fgets) then fputs a PHP line, and then offer the file to download.
Problem is, the line is not inserted after line 19 but at the end of the .php file. Here is the code:
if (is_writable($filename)) {
if (!$handle = fopen($filename, 'a+')) {
echo "Cannot open file ($filename)";
exit;
}
for ($i = 1; $i <= 19; $i++) {
$offset = fgets($handle);
}
if (fwrite($handle, $somecontent) === FALSE) {
exit;
}
fclose($handle);
}
What would you do ?
append mode +a in fopen() places the handle's pointer at the end of the file. Your fgets() loop will fail as there's nothing left to read at the end of the file. You're basically doing 19 no-ops. Your fwrite will then output your new value at the end of the file, as expected.
To do your insert, you'd need to rewind() the handle to the beginning, then do your fgets() loop.
However, if you're just wanting people to get this modified file, why bother doing the "open file, scan through, write change, serve up file"? This'd leave a multitude of near-duplicates on your system. A better method would be to split your file into two parts, and then you could do a simple:
readfile('first_part.txt');
echo "The value you want to insert";
readfile('last_part.txt');
which saves you having to save the 'new' file each time. This would also allow arbitrary length inserts. Your fwrite method could potentially trash later parts of the file. e.g. You scan to offset "10" and write out 4 bytes, which replaces the original 4 bytes at that location in the original file. At some point, maybe it turns into 5 bytes of output, and now you've trashed a byte in the original and maybe have a corrupted file.
The a+ mode means:
'a+' Open for reading and writing; place the file pointer at the end of the file. If the file does not exist, attempt to create it.
You probably want r+
'r+' Open for reading and writing; place the file pointer at the beginning of the file.
Put your desired code in one string variable. Where you will have %s at point where you want to customize your code. After that just respond with php MIME type.
eg;
$phpCode = "if (foo == blah) { lala lala + 4; %s = 5; }", $user_specific_variable;
header('Content-type: text/php');
echo $phpCode;
Voila.
NB: Maybe mime type is not correct, I am talking out of my ass here.
I think instead of opening the file in "a+" mode, you should open the file in "r+" mode, because "a" always appends to the file. But I think the write will anyways overwrite your current data. So, the idea is that you'll need to buffer the file, from the point where you intend to write to the EOF. Then add your line followed by what you had buffered.
Another approach might be to keep some pattern in your PHP file, like ######. You can then:
1. copy the original PHP script
2. read the complete PHP script into a single variable, say $fileContent, using file_get_contents()
3. use str_replace() function to replace ###### in $fileContent with desired User ID
4. open the copied PHP script in "a" mode and rewrite $fileContent to it.
I want to merge two large CSV files with PHP. This files are too big to even put into memory all at once. In pseudocode, I can think of something like this:
for i in file1
file3.write(file1.line(i) + ',' + file2.line(i))
end
But when I'm looping through a file using fgetcsv, it's not really clear how I would grab line n from a certain file without loading the whole thing into memory first.
Any ideas?
Edit: I forgot to mention that each of the two files has the same number of lines and they have a one-to-one relationship. That is, line 62,324 in file1 goes with line 62,324 in file2.
Not sure what operating system you're on, but if you're using Linux, using the paste command is probably a lot easier than trying to do this in PHP.
If this is a viable solution and you don't absolutely need to do it in PHP, you could try the following:
paste -d ',' file1 file2 > combined_file
Take a look at the fgets function. You could read a single line of each file, process them, and write them to your new file, then move on to the next line until you've reached the end of your file.
PHP: fgets
Specifically look at the example titled Example #1 Reading a file line by line in the PHP manual. It's also important to note the return value of the the fgets functions.
Returns a string of up to length - 1
bytes read from the file pointed to by
handle. If there is no more data to
read in the file pointer, then FALSE
is returned.
So, if it doesn't return FALSE you know you still have more lines to process.
You can use fgets().
$file1 = fopen('file1.txt', 'r');
$file2 = fopen('file2.txt', 'r');
$merged = fopen('merged.txt', 'w');
while (
($line1 = fgets($file1)) !== false
&& ($line2 = fgets($file2)) !== false) {
fwrite($merged, $line1 . ',' . $line2);
}
fgets() reads one line from a file. As you can see, this code uses it on both files at the same time, writing the merged lines to a third file. The manual here:
http://php.net/fgets
http://php.net/fopen
http://php.net/fwrite
Try using fgets() to read one line from each file at a time.
I think the solution for this is to map first line begins for each line ( and some kind of key if you need ) and then make a new csv using fread and fwrite ( we know beginning and ending of each line now , so we need just seek and read )
Another way is to put it into MySQL ( if it is possible ) and then back to new CSV
What is the best way to overwrite a specific line in a file? I basically want to search a file for the string '#parsethis' and overwrite the rest of that line with something else.
If the file is really big (log files or something like this) and you are willing to sacrifice speed for memory consumption you could open two files and essentially do the trick Jeremy Ruten proposed by using files instead of system memory.
$source='in.txt';
$target='out.txt';
// copy operation
$sh=fopen($source, 'r');
$th=fopen($target, 'w');
while (!feof($sh)) {
$line=fgets($sh);
if (strpos($line, '#parsethis')!==false) {
$line='new line to be inserted' . PHP_EOL;
}
fwrite($th, $line);
}
fclose($sh);
fclose($th);
// delete old source file
unlink($source);
// rename target file to source file
rename($target, $source);
If the file isn't too big, the best way would probably be to read the file into an array of lines with file(), search through the array of lines for your string and edit that line, then implode() the array back together and fwrite() it back to the file.
Your main problem is the fact that the new line may not be the same length as the old line. If you need to change the length of the line, there is no way out of rewriting at least all of the file after the changed line. The easiest way is to create a new, modified file and then move it over the original. This way there is a complete file available at all times for readers. Use locking to make sure that only one script is modifying the file at once, and since you are going to replace the file, do the locking on a different file. Check out flock().
If you are certain that the new line will be the same length as the old line, you can open the file in read/write mode (use r+ as the second argument to fopen()) and call ftell() to save the position the line starts at each time before you call fgets() to read a line. Once you find the line that you want to overwrite, you can use fseek() to go back to the beginning of the line and fwrite() the new data. One way to force the line to always be the same length is to space pad it out to the maximum possible length.
This is a solution that works for rewriting only one line of a file in place with sed from PHP. My file contains only style vars and is formatted:
$styleVarName: styleVarProperty;\n
For this I first add the ":" to the ends of myStyleVarName, and sed replaces the rest of that line with the new property and adds a semicolon.
Make sure characters are properly escaped in myStyleVarProp.
$command = "pathToShellScript folder1Name folder2Name myStyleVarName myStyleVarProp";
shell_exec($command);
/* shellScript */
#!/bin/bash
file=/var/www/vhosts/mydomain.com/$1/$2/scss/_variables.scss
str=$3"$4"
sed -i "s/^$3.*/$str;/" $file
or if your file isn't too big:
$sample = file_get_contents('sample');
$parsed =preg_replace('##parsethis.*#', 'REPLACE TO END OF LINE', $sample);
You'll have to choose delimiters '#' that aren't present in the file though.
If you want to completely replace the contents of one file with the contents of another file you can use this:
rename("./some_path/data.txt", "./some_path/data_backup.txt");
rename("./some_path/new_data.txt", "./some_path/data.txt");
So in the first line you backup the file and in the second line you replace the file with the contents of a new file.
As far as I can tell the rename returns a boolean. True if the rename is successful and false if it fails. One could, therefore, only run the second step if the first step is successful to prevent overwriting the file unless a backup has been made successfully. Check out:
https://www.php.net/manual/en/function.rename.php
Hope that is useful to someone.
Cheers
Adrian
I'd most likely do what Jeremy suggested, but just for an alternate way to do it here is another solution. This has not been tested or used and is for *nix systems.
$cmd = "grep '#parsethis' " . $filename;
$output = system($cmd, $result);
$lines = explode("\n", $result);
// Read the entire file as a string
// Do a str_repalce for each item in $lines with ""