As far as I am understanding c/c+ mode, I am expecting behaviour like 'a/a+ mode, so the file shouldn't be truncated, and any fwrite() result should be prepended to existing file.
In fact the file seems to be truncated anyway as the file always contains only tle last fwrite() content anyway.
Is it a possible bug in my PHP version (7.0), or I am misunderstanding something?
<?php
$fp = fopen($fpath,'c+');
fwrite($fp, date("H:i:s")." test\n");
fclose($fp);
What makes you think that this should behave different? According to the documentation, using c the pointer is "positioned on the beginning of the file". Starting to write from that specific position, you would always override whatever is already present in that file
Maybe a small addition to what has been said:
<?php
/* file test.txt contains string(4): 'test' */
$fp = fopen('test.txt','c+');
fclose($fp);
file test.txt is NOT truncated to zero length(as w or w+ would do on fopen() ),
it still contains string(4): test
Now see what happens when we write one character to the file using c+
$fp = fopen('test.txt','c+');
fwrite($fp, 'b');
fclose($fp);
file test.txt now contains: best, the file pointer was positioned at the beginning of the file and only overwrites the first character in the original - test has become best
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 am trying to write a text at a specific position in a file that already has some content. After writing I find the file truncated to the size of the text plus fseek position and the first characters with value 0. Is this the normal behaviour or am I missing something? I want to mention that I'm trying to avoid loading the file into memory and writing it back.
$file = fopen("text.txt","w");
fseek($file,3);
fwrite($file,"Hello");
fclose($file);
You need to open the file in c mode, else it's truncated on fopen:
$file = fopen("text.txt","c");
See http://php.net/manual/de/function.fopen.php for a documentation of all file open modes and what exactly they do. Also see the http://www.php.net/manual/en/function.fseek.php manual
Yes this is normal behaviour :
fopen($file, "w"):
place the file pointer at the beginning of the file and truncate the file to zero length.
fseek():
In general, it is allowed to seek past the end-of-file; if data is then written, reads in any unwritten region between the end-of-file and the sought position will yield bytes with value 0. [..]
If you have opened the file in append (a or a+) mode, any data you write to the file will always be appended, regardless of the file position, and the result of calling fseek() will be undefined.
You probably want to open the file in a non truncating write mode (e.g. "c" but not "a").
I want to wite to a text file at the inputed text position using PHP. I tried using fseek to point the wite position to the inputed number, but it saves as an empty file instead.
<?php
$testData = "testdata";
$testPosition = 3;
$fileReference = fopen("test.txt", "w");
fseek($fileReference, $testPosition);
fwrite($fileReference, $testData);
fclose($fileReference);
?>
How would I get the script to wite to the text file at the specified position correctly?
The w flag only allows for writing to a file. Try replacing the w flag with a r+ flag. This will allow for read/write to a file without truncating the file. the read /write is needed to allows you to go search for your caret and write to where it is. for more information on the fopen function please see php.net: fopen()
The w flag has this functionality:
'w' Open for writing only; place the file pointer at the beginning of the file and truncate the file to zero length. If the file does not exist, attempt to create it.
This could be why you're getting an empty file.
However, on my local server, this works fine. This makes me think your permissions may not be correct. For example, you might not have write permissions. Try and ensure that you have the correct permissions on this file.
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.
The following code supposed to add at the beginning of my php files on the webserver the string abcdef.
However it replaces all the content with the abcdef. How can I correct it?
Also how can I add something on the end instead of the beginning?
foreach (glob("*.php") as $file) {
$fh = fopen($file, 'c'); //Open file for writing, place pointer at start of file.
fwrite($fh, 'abcdef');
fclose($fh);
}
You just need to open the file with a flag that allows you to write without truncating the file to zero length:
$fh = fopen($file, 'r+');
However it replaces all the content with the abcdef. How can I correct it?
From the documentation for fopen on the "c" mode:
Open the file for writing only. If the file does not exist, it is created. If it exists, it is neither truncated (as opposed to 'w'), nor the call to this function fails (as is the case with 'x'). The file pointer is positioned on the beginning of the file.
When you write 'abcdef' to the file, it will overwrite the first six characters. To prepend text, you'll need to copy the existing content, either by reading it out before writing the additional text, or by:
creating a new file,
writing the new text,
then copying over the old content,
then removing the old file and
renaming the new.
Also how can I add something on the end instead of the begining?
Use the append mode: "a".