Reading files (fread, fgets, file) in PHP

Introduction

Reading files lets your program get information stored in text files. This helps you use data saved earlier or from other sources.

You want to read a list of names saved in a text file.

You need to process a log file line by line to find errors.

You want to load configuration settings stored in a file.

You want to read the entire content of a file into a variable quickly.

You want to read a file line by line to save memory.

Syntax

PHP

<?php
// Open a file for reading
$handle = fopen('filename.txt', 'r');

// Read fixed number of bytes
$content = fread($handle, 100);

// Read one line
$line = fgets($handle);

// Close the file
fclose($handle);

// Read entire file into array of lines
$lines = file('filename.txt');
?>

fopen opens the file and returns a handle to use for reading.

fread reads a set number of bytes from the file.

fgets reads one line at a time.

file reads the whole file into an array, each element is a line.

Examples

Reads first 50 bytes from 'data.txt' and prints it.

PHP

<?php
$handle = fopen('data.txt', 'r');
$content = fread($handle, 50);
fclose($handle);
echo $content;
?>

Reads 'data.txt' line by line and prints each line.

PHP

<?php
$handle = fopen('data.txt', 'r');
while (($line = fgets($handle)) !== false) {
    echo $line;
}
fclose($handle);
?>

Reads entire file into an array, then prints each line.

PHP

<?php
$lines = file('data.txt');
foreach ($lines as $line) {
    echo $line;
}
?>

Sample Program

This program creates a small file, then reads it three ways: first 10 bytes with fread, line by line with fgets, and all lines at once with file. It prints the results so you can see how each method works.

PHP

<?php
// Sample program to read a file using fread, fgets, and file

// Create a sample file
file_put_contents('sample.txt', "Hello\nWorld\nPHP File Reading!\n");

// Using fread
$handle = fopen('sample.txt', 'r');
$content = fread($handle, 10); // read first 10 bytes
fclose($handle);
echo "Using fread (10 bytes):\n" . $content . "\n\n";

// Using fgets
$handle = fopen('sample.txt', 'r');
$line1 = fgets($handle); // read first line
$line2 = fgets($handle); // read second line
fclose($handle);
echo "Using fgets (line by line):\n" . $line1 . $line2;

// Using file
$lines = file('sample.txt');
echo "Using file (all lines):\n";
foreach ($lines as $line) {
    echo $line;
}

// Clean up sample file
unlink('sample.txt');

Important Notes

Always close files with fclose() after reading to free resources.

fread() reads bytes, so it may cut off in the middle of a line.

fgets() reads one line at a time, including the newline character.

Summary

Use fread() to read a specific number of bytes from a file.

Use fgets() to read a file line by line.

Use file() to read the whole file into an array of lines easily.

Practice

1. Which PHP function reads a file line by line, returning one line at a time?

easy

A. fopen()

B. fread()

C. file()

D. fgets()

Solution

1. Step 1: Understand function behavior

   fgets() reads a file one line at a time, useful for line-by-line processing.

2. Step 2: Compare with other functions

   fread() reads bytes, file() reads whole file into array, fopen() opens file but does not read.

3. Final Answer:

   fgets() -> Option D

4. Quick Check:

   Line-by-line reading = fgets() [OK]

Hint: fgets() reads one line at a time from a file [OK]

Common Mistakes:

• Confusing fread() with fgets()
• Thinking file() reads line by line
• Using fopen() to read data directly

2. Which of the following is the correct syntax to read 100 bytes from a file pointer $fp using fread()?

easy

A. fread($fp);

B. fread(100, $fp);

C. fread($fp, 100);

D. fread(100);

Solution

1. Step 1: Recall fread() parameter order

   fread() takes the file pointer first, then the number of bytes to read.

2. Step 2: Validate syntax correctness

   Only fread($fp, 100); matches the correct order and required parameters.

3. Final Answer:

   fread($fp, 100); -> Option C

4. Quick Check:

   fread(fp, bytes) syntax = fread($fp, 100); [OK]

Hint: fread() needs file pointer first, then byte count [OK]

Common Mistakes:

• Swapping parameters order
• Omitting byte count
• Passing only one argument

3. What will be the output of the following PHP code if the file data.txt contains:

Line1
Line2
Line3

Code:

$lines = file('data.txt');
echo trim($lines[1]);

medium

A. Line2

B. Line1

C. Line3

D. Error

Solution

1. Step 1: Understand file() output

   file() reads the whole file into an array, each element is a line including newline.

2. Step 2: Access second line and trim

   $lines[1] is the second line "Line2\n"; trim() removes newline, so output is "Line2".

3. Final Answer:

   Line2 -> Option A

4. Quick Check:

   file()[1] trimmed = Line2 [OK]

Hint: file() returns array of lines, index 1 is second line [OK]

Common Mistakes:

• Confusing array index starting at 0
• Not trimming newline characters
• Expecting fread() output instead

4. Identify the error in this PHP code snippet that tries to read the first 10 bytes of a file:

$fp = fopen('file.txt', 'r');
$content = fread(10, $fp);
echo $content;

medium

A. fopen() mode should be 'rb' instead of 'r'

B. Parameters of fread() are reversed

C. fread() requires a third parameter

D. fopen() returns false, file not opened

Solution

1. Step 1: Check fread() parameter order

   fread() expects file pointer first, then number of bytes. Here they are reversed.

2. Step 2: Confirm other parts

   fopen('file.txt', 'r') is valid for reading text files; no third parameter needed; no info about fopen failure.

3. Final Answer:

   Parameters of fread() are reversed -> Option B

4. Quick Check:

   fread(fp, bytes) order matters [OK]

Hint: fread() needs file pointer first, then bytes [OK]

Common Mistakes:

• Swapping fread() arguments
• Assuming fopen() mode error without evidence
• Expecting extra fread() parameters

5. You want to read a text file and print only the lines that contain the word "error" (case-insensitive). Which approach is best in PHP?

hard

A. Use fgets() in a loop, check each line with stripos()

B. Use fread() to read entire file as bytes, then search for "error"

C. Use file() to read all lines, then loop and check each line with stripos()

D. Use fopen() and print file pointer directly

Solution

1. Step 1: Consider memory and line processing

   fgets() reads line by line, efficient for large files and allows checking each line.

2. Step 2: Use stripos() for case-insensitive search

   Inside the loop, stripos() finds "error" ignoring case, so only matching lines are printed.

3. Final Answer:

   Use fgets() in a loop, check each line with stripos() -> Option A

4. Quick Check:

   Line-by-line read + case-insensitive check = fgets() + stripos() [OK]

Hint: Use fgets() loop with stripos() for line filtering [OK]

Common Mistakes:

• Using fread() for line filtering
• Reading whole file into memory unnecessarily
• Printing file pointer instead of content