PHP
Writing with file_put_contents()
Learn to write a string to a file with file_put_contents().
Writing files with file_put_contents()
To write a string to a file you use the file_put_contents() function. It takes two arguments: the file path and the content to write.
For example, file_put_contents('log.txt', 'Hello'); writes 'Hello' into log.txt. If the file does not exist it is created; if it exists its content is overwritten.
The function returns the number of bytes written. If it returns false, the write failed.
Appending with the FILE_APPEND flag
If you want to add new content to the end of the file instead of overwriting it, pass the FILE_APPEND flag as the third argument.
For example, file_put_contents('log.txt', 'New entry' . PHP_EOL, FILE_APPEND); appends the line 'New entry' to log.txt. The existing content is preserved. PHP_EOL is the end-of-line character (\n on Linux).
This pattern is very useful for log files: each new entry is appended to the end, old entries are kept.
Exercise Write the file and read it back
Use file_put_contents() to write the string 'Entry added' to log.txt. Then read the file with file_get_contents() and print it with echo. Use __DIR__ in the path argument of both functions.
Show example solution
First write file_put_contents(__DIR__ . '/log.txt', 'Entry added'); then echo file_get_contents(__DIR__ . '/log.txt');.
Example solution:
<?php
// Write to the file
file_put_contents(__DIR__ . '/log.txt', 'Entry added');
// Read and print
echo file_get_contents(__DIR__ . '/log.txt');
Test yourself
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If file_put_contents('a.txt', 'x') is called and a.txt already exists, what happens?
- The file is replaced with 'x' (overwritten)
- 'x' is appended to the end of the file
- PHP throws an error and leaves the file untouched
- The content 'xx' is written instead of 'x'
Show answer
The file is replaced with 'x' (overwritten) — Correct. file_put_contents() overwrites the file by default; the old content is lost.
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Append the entry to the file
file_put_contents('log.txt', $msg . PHP_EOL, ____);
Show answer
file_put_contents('log.txt', $msg . PHP_EOL, FILE_APPEND);
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Match file_put_contents concepts
- file_put_contents()
- Writes a string to a file
- First argument
- Is the file path
- Second argument
- Is the content to write
- FILE_APPEND
- Appends to the end
Next lesson: Opening files with fopen()
