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Walrus provides file I/O capabilities through the std/io module. This example demonstrates reading and writing files using both convenience functions and handle-based operations.

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Basic file operations

The simplest way to work with files is using the convenience functions: 
import "std/io";

// Write to a file
io.write_file("hello.txt", "Hello, Walrus!");

// Read from a file
let content = io.read_file("hello.txt");
println(content);

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How to run

Save the code to a file called file_io.walrus and run it: 
walrus file_io.walrus

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Expected output

Hello, Walrus!

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Handle-based operations

For more control, especially with larger files or streaming operations, use file handles: 
import "std/io";

// Write using handles
let handle = io.file_open("data.txt", "w");
io.file_write(handle, "Line 1\n");
io.file_write(handle, "Line 2\n");
io.file_write(handle, "Line 3\n");
io.file_close(handle);

// Read using handles
let reader = io.file_open("data.txt", "r");
let line = io.file_read_line(reader);
while line != void {
    println(line);
    line = io.file_read_line(reader);
}
io.file_close(reader);

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Output

Line 1
Line 2
Line 3

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File existence check

You can check if a file exists before reading: 
import "std/io";

if io.file_exists("/tmp/test_walrus.txt") {
    let content = io.read_file("/tmp/test_walrus.txt");
    println("File contents: " + content);
} else {
    println("File does not exist!");
}

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Complete example

Here’s a complete example that demonstrates all file operations: 
import "std/io";

// Write a file
io.write_file("/tmp/test_walrus.txt", "Hello from Walrus!");

// Read it back
let content = io.read_file("/tmp/test_walrus.txt");
println(content);

// Check if files exist
println(io.file_exists("/tmp/test_walrus.txt"));  // true
println(io.file_exists("/tmp/nonexistent_file.txt"));  // false

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Output

Hello from Walrus!
true
false

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Available functions

FunctionDescription
io.file_open(path, mode)Open a file, returns a handle. Modes: "r", "w", "a", "rw"
io.file_read(handle)Read entire file contents as string
io.file_read_line(handle)Read a single line (returns void at EOF)
io.file_write(handle, content)Write string to file, returns bytes written
io.file_close(handle)Close a file handle
io.file_exists(path)Check if a file exists (returns bool)
io.read_file(path)Convenience: read entire file in one call
io.write_file(path, content)Convenience: write entire file in one call

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Key concepts

  • Import statement: Use import "std/io" to access file I/O functions
  • File modes: "r" for reading, "w" for writing, "a" for appending, "rw" for read-write
  • Void type: file_read_line returns void when reaching end of file
  • Handle management: Always close file handles when done

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