wren/manual_src/pages/howto/file-operations.html

{# retoor <retoor@molodetz.nl> #}
{% extends 'page.html' %}

{% set page_title = "File Operations" %}
{% set breadcrumb = [{"url": "howto/index.html", "title": "How-To Guides"}, {"title": "File Operations"}] %}
{% set prev_page = {"url": "howto/regex-patterns.html", "title": "Regex Patterns"} %}
{% set next_page = {"url": "howto/async-operations.html", "title": "Async Operations"} %}

{% block article %}
                <h1>File Operations</h1>

                <h2>Read Entire File</h2>
                <pre><code>import "io" for File

var content = File.read("document.txt")
System.print(content)</code></pre>

                <h2>Write to File</h2>
                <pre><code>import "io" for File

File.write("output.txt", "Hello, World!")
System.print("File written!")</code></pre>

                <h2>Append to File</h2>
                <pre><code>import "io" for File

var existing = File.exists("log.txt") ? File.read("log.txt") : ""
File.write("log.txt", existing + "New line\n")</code></pre>

                <h2>Check if File Exists</h2>
                <pre><code>import "io" for File

if (File.exists("config.txt")) {
    System.print("Config found")
    var content = File.read("config.txt")
} else {
    System.print("Config not found, using defaults")
}</code></pre>

                <h2>Get File Size</h2>
                <pre><code>import "io" for File

var size = File.size("data.bin")
System.print("File size: %(size) bytes")</code></pre>

                <h2>Copy File</h2>
                <pre><code>import "io" for File

File.copy("source.txt", "destination.txt")
System.print("File copied!")</code></pre>

                <h2>Rename/Move File</h2>
                <pre><code>import "io" for File

File.rename("old_name.txt", "new_name.txt")
System.print("File renamed!")

File.rename("file.txt", "subdir/file.txt")
System.print("File moved!")</code></pre>

                <h2>Delete File</h2>
                <pre><code>import "io" for File

if (File.exists("temp.txt")) {
    File.delete("temp.txt")
    System.print("File deleted!")
}</code></pre>

                <h2>List Directory Contents</h2>
                <pre><code>import "io" for Directory

var files = Directory.list(".")

for (file in files) {
    System.print(file)
}</code></pre>

                <h2>Check if Directory Exists</h2>
                <pre><code>import "io" for Directory

if (Directory.exists("data")) {
    System.print("Directory found")
} else {
    System.print("Directory not found")
}</code></pre>

                <h2>Create Directory</h2>
                <pre><code>import "io" for Directory

if (!Directory.exists("output")) {
    Directory.create("output")
    System.print("Directory created!")
}</code></pre>

                <h2>Delete Empty Directory</h2>
                <pre><code>import "io" for Directory

Directory.delete("empty_folder")
System.print("Directory deleted!")</code></pre>

                <h2>Read File Line by Line</h2>
                <pre><code>import "io" for File

var content = File.read("data.txt")
var lines = content.split("\n")

for (line in lines) {
    if (line.count > 0) {
        System.print(line)
    }
}</code></pre>

                <h2>Process Files in Directory</h2>
                <pre><code>import "io" for File, Directory

var files = Directory.list("./data")

for (filename in files) {
    if (filename.endsWith(".txt")) {
        var path = "./data/%(filename)"
        var content = File.read(path)
        System.print("%(filename): %(content.count) chars")
    }
}</code></pre>

                <h2>Recursive Directory Listing</h2>
                <pre><code>import "io" for File, Directory

var listRecursive = Fn.new { |path, indent|
    var items = Directory.list(path)

    for (item in items) {
        var fullPath = "%(path)/%(item)"
        System.print("%(indent)%(item)")

        if (Directory.exists(fullPath)) {
            listRecursive.call(fullPath, indent + "  ")
        }
    }
}

listRecursive.call(".", "")</code></pre>

                <h2>Find Files by Extension</h2>
                <pre><code>import "io" for File, Directory

var findByExtension = Fn.new { |path, ext|
    var results = []
    var items = Directory.list(path)

    for (item in items) {
        var fullPath = "%(path)/%(item)"

        if (Directory.exists(fullPath)) {
            var subResults = findByExtension.call(fullPath, ext)
            for (r in subResults) results.add(r)
        } else if (item.endsWith(ext)) {
            results.add(fullPath)
        }
    }

    return results
}

var wrenFiles = findByExtension.call(".", ".wren")
for (file in wrenFiles) {
    System.print(file)
}</code></pre>

                <h2>Read JSON Configuration</h2>
                <pre><code>import "io" for File
import "json" for Json

var loadConfig = Fn.new { |path, defaults|
    if (!File.exists(path)) {
        return defaults
    }

    var content = File.read(path)
    var config = Json.parse(content)

    for (key in defaults.keys) {
        if (!config.containsKey(key)) {
            config[key] = defaults[key]
        }
    }

    return config
}

var config = loadConfig.call("config.json", {
    "port": 8080,
    "debug": false
})

System.print("Port: %(config["port"])")</code></pre>

                <h2>Save JSON Configuration</h2>
                <pre><code>import "io" for File
import "json" for Json

var config = {
    "database": "app.db",
    "port": 8080,
    "debug": true
}

File.write("config.json", Json.stringify(config, 2))
System.print("Configuration saved!")</code></pre>

                <h2>Create Backup Copy</h2>
                <pre><code>import "io" for File
import "datetime" for DateTime

var backup = Fn.new { |path|
    if (!File.exists(path)) {
        System.print("File not found: %(path)")
        return null
    }

    var timestamp = DateTime.now().format("\%Y\%m\%d_\%H\%M\%S")
    var backupPath = "%(path).%(timestamp).bak"

    File.copy(path, backupPath)
    System.print("Backup created: %(backupPath)")

    return backupPath
}

backup.call("important.txt")</code></pre>

                <h2>Read User Input</h2>
                <pre><code>import "io" for Stdin

System.write("Enter your name: ")
var name = Stdin.readLine()

System.print("Hello, %(name)!")</code></pre>

                <h2>Interactive Menu</h2>
                <pre><code>import "io" for Stdin

System.print("Select an option:")
System.print("1. Option A")
System.print("2. Option B")
System.print("3. Exit")

System.write("Choice: ")
var choice = Stdin.readLine()

if (choice == "1") {
    System.print("You selected Option A")
} else if (choice == "2") {
    System.print("You selected Option B")
} else if (choice == "3") {
    System.print("Goodbye!")
}</code></pre>

                <h2>Safe File Operations with Error Handling</h2>
                <pre><code>import "io" for File

var safeRead = Fn.new { |path|
    var fiber = Fiber.new { File.read(path) }
    var result = fiber.try()

    if (fiber.error) {
        System.print("Error reading %(path): %(fiber.error)")
        return null
    }

    return result
}

var content = safeRead.call("maybe_exists.txt")
if (content) {
    System.print("Content: %(content)")
}</code></pre>

                <h2>Calculate Directory Size</h2>
                <pre><code>import "io" for File, Directory

var dirSize = Fn.new { |path|
    var total = 0
    var items = Directory.list(path)

    for (item in items) {
        var fullPath = "%(path)/%(item)"

        if (Directory.exists(fullPath)) {
            total = total + dirSize.call(fullPath)
        } else if (File.exists(fullPath)) {
            total = total + File.size(fullPath)
        }
    }

    return total
}

var size = dirSize.call(".")
System.print("Total size: %(size) bytes")</code></pre>

                <div class="admonition tip">
                    <div class="admonition-title">See Also</div>
                    <p>For full API documentation, see the <a href="../api/io.html">IO module reference</a>. For object-oriented path manipulation with glob, walk, and tree operations, see the <a href="../api/pathlib.html">pathlib module reference</a>.</p>
                </div>
{% endblock %}