PHP: how to write in between content of existing file?

Question

How to write in between content of existing file?

I tried to use fseek() to seek a new position and write the new content, but it replaces old content to the new string after seek position.

My aim is to put new contents after 5 characters of existing file.

Old content: AAAAABBBBB, desired content: AAAAAnewcontentBBBBB

$file_handler = fopen('putty.log','w');
$new_content = 'this is new content';

fseek($file_handler,5);

echo ftell($file_handler); //5
fwrite($file_handler,$new_content);

old content replaced with NULLNULLNULLNULLNULLthis is new content

Link stackoverflow.com/q/6472408/1338846

Sampo Sarrala
– Sampo Sarrala

2012-05-11 18:59:33 +00:00
Commented May 11, 2012 at 18:59 — Sampo Sarrala
– Sampo Sarrala, Commented May 11, 2012 at 18:59

Riccardo Galli · Accepted Answer · 2011-12-25 14:18:58Z

1

You can't do it that way.

You can only truncate the content with ftruncate and write later the old content

A not so clean example

<?php

$file_handler = fopen('putty.log','rb+');
$new_content = 'this is new content';

fseek($file_handler,5);

$restOfContent = fread($file_handler,filesize('putty.log')-5);

ftruncate($file_handler,5);
fseek($file_handler,5);

echo ftell($file_handler); //5
fwrite($file_handler,$new_content);

fwrite($file_handler,$restOfContent);

fclose($file_handler)

edited Dec 25, 2011 at 14:18

answered Dec 25, 2011 at 14:06

Riccardo Galli

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2 Comments

P K Over a year ago

don't we need to rewind() after fread($file_handler,filesize('putty.log')-5);? or after reading EOF if we seek again it starts from beginning?

P K Over a year ago

i think when file pointer reaches EOF and i seek again, it starts from 0.

Svisstack · Accepted Answer · 2011-12-25 14:10:37Z

1

Load contents to variable using file_get_contents().
Do this on your buffer.
Save your contents to this file using file_put_contents();

answered Dec 25, 2011 at 14:10

Svisstack

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2 Comments

P K Over a year ago

yup that's memory burden if file is huge.

Svisstack Over a year ago

yes but fastest development ;-) think about how code will be used in lifetime, because maybe this can be better solution in relation to your time what you spend on that

Alireza · Accepted Answer · 2011-12-25 14:24:04Z

1

if you're using fseek() to write data to a file, remember to open the file in "r+" mode, example:

$fp=fopen($filename,"r+");

answered Dec 25, 2011 at 14:24

Alireza

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2 Comments

P K Over a year ago

thanks, i guess w mode always truncate file to zero length in beginning.

Alireza Over a year ago

w actually overwrites the existing file.

Yaniro · Accepted Answer · 2011-12-25 14:28:20Z

Writing in the middle of the file won't cause it to stretch and push the content forward (like when inserting content in a text editor) but rather to overwrite the content at the position you start writing. What you need to do is:

read the first part of the old data until the point where you need to write the new content & write that part to a temporary file.
write the new content to the temporary file (the stuff you wish to add).
read the rest of the content from the old file & write it to the temporary file.
delete the old file.
rename the temporary file to the name of the old file.

Example:

$original_file_name = '/tmp/putty.log';
$temp_file_name = '/tmp/putty.tmp';
$temp_file = fopen( $temp_file_name, 'w' );
$file_handler = fopen( $original_file_name, 'r' );
$old_data_size = 5;
fwrite( $temp_file, fread( $file_handler, $old_data_size ) );
$new_content = 'this is new content';
fwrite( $temp_file, $new_content, strlen( $new_content ) );
fwrite( $temp_file, fread( $file_handler, filesize( $original_file_name ) - $old_data_size ) );
fclose( $file_handler );
fclose( $temp_file );
unlink( $original_file_name );
rename( $temp_file_name, $original_file_name );

Make sure that putty.log has read/write permissions for the user used by your webserver (apache/lighttpd etc.) process or that it's accessible for everyone (not recommended).

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