php can write or append data to the file through fopen or file_put_contents. Let me introduce the fopen method:
The fopen() function opens a file or URL. If the opening fails, this function returns FALSE.

I. Grammar:

Syntax: fopen(filename,mode,include_path,context)

filename Required.Specifies the file or URL to open.mode Required.Specifies the type of access required to this file/stream.Possible values ​​are shown in the table below.include_path is optional.This parameter can be set to 1 or TRUE if the file needs to be retrieved in include_path as well.context is optional.Specifies the environment for the file handle.Context is a set of options that can modify the behavior of the stream.

Possible values ​​for the mode parameter: "r", "r+", "w", "w+", "a", "a+", "x", "x+"

“r”: Open in read-only mode, and point the file pointer to the file header."r+": Open for reading and writing, and point the file pointer to the file header."w": Open for writing, point the file pointer to the file header and truncate the file size to zero.if the document does not exist, try to create it."w+": Open for reading and writing, point the file pointer to the file header and truncate the file size to zero.if the document does not exist, try to create it."a": Open for writing, point the file pointer to the end of the file.if the document does not exist, try to create it."a+": Open for reading and writing, and point the file pointer to the end of the file.if the document does not exist, try to create it."x": Create and open for writing, pointing the file pointer to the file header.If the file already exists, the fopen() call fails and returns FALSE with an E_WARNING level error message.if the document does not exist, try to create it."x+": Create and open for read-write, pointing the file pointer to the file header.If the file already exists, the fopen() call fails and returns FALSE with an E_WARNING level error message.if the document does not exist, try to create it.

Write content as appends

$fp = fopen('test.txt','a');//fwrite($fp, 'I am appending the content'.PHP_EOL);//PHP_EOL newlinefclose($fp);