System.IO.File F# snippets (#8627)

* File F# snippets

* fix build

Author: albert-du

snippets/fsharp/System.IO/File/AppendAllLines/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="program.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.IO/File/AppendAllLines/program.fs

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+module program
+// <Snippet1>
+open System
+open System.IO
+
+let dataPath = @"c:\temp\timestamps.txt"
+
+let createSampleFile () =
+    let timeStamp = DateTime(1700, 1, 1)
+
+    use sw = new StreamWriter(dataPath)
+
+    for i = 0 to 499 do
+        let ts1 = timeStamp.AddYears i
+        let ts2 = ts1.AddMonths i
+        let ts3 = ts2.AddDays i
+        ts3.ToLongDateString() |> sw.WriteLine
+
+createSampleFile ()
+
+let julyWeekends =
+    File.ReadLines dataPath
+    |> Seq.filter (fun line ->
+        (line.StartsWith "Saturday"
+         || line.StartsWith "Sunday")
+        && line.Contains "July")
+
+File.WriteAllLines(@"C:\temp\selectedDays.txt", julyWeekends)
+
+let marchMondays =
+    File.ReadLines dataPath
+    |> Seq.filter (fun line -> line.StartsWith "Monday" && line.Contains "March")
+
+File.AppendAllLines(@"C:\temp\selectedDays.txt", marchMondays)
+
+// </Snippet1>

snippets/fsharp/System.IO/File/AppendAllText/AllText.fs

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+module AllText
+//<snippet00>
+open System
+open System.IO
+
+let path = @"c:\temp\MyTest.txt"
+
+// This text is added only once to the file.
+if File.Exists path |> not then
+    // Create a file to write to.
+    let createText =
+        "Hello and Welcome" + Environment.NewLine
+
+    File.WriteAllText(path, createText)
+
+// This text is always added, making the file longer over time
+// if it is not deleted.
+let appendText =
+    "This is extra text" + Environment.NewLine
+
+File.AppendAllText(path, appendText)
+
+// Open the file to read from.
+let readText = File.ReadAllText path
+printfn $"{readText}"
+//</snippet00>

snippets/fsharp/System.IO/File/AppendAllText/AllText1.fs

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+module AllText1
+//<snippet00>
+open System
+open System.IO
+open System.Text
+
+let path = @"c:\temp\MyTest.txt"
+
+// This text is added only once to the file.
+if File.Exists path |> not then
+    // Create a file to write to.
+    let createText =
+        "Hello and Welcome" + Environment.NewLine
+
+    File.WriteAllText(path, createText, Encoding.UTF8)
+
+// This text is always added, making the file longer over time
+// if it is not deleted.
+let appendText =
+    "This is extra text" + Environment.NewLine
+
+File.AppendAllText(path, appendText, Encoding.UTF8)
+
+// Open the file to read from.
+let readText = File.ReadAllText path
+printfn $"{readText}"
+//</snippet00>

snippets/fsharp/System.IO/File/AppendAllText/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="AllText.fs" />
+    <Compile Include="AllText1.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.IO/File/AppendText/file_appendtext.fs

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+module file_appendtext
+// <Snippet1>
+open System.IO
+
+let path = @"c:\temp\MyTest.txt"
+
+// This text is added only once to the file.
+if File.Exists path |> not then
+    // Create a file to write to.
+    use sw = File.CreateText path
+    sw.WriteLine "Hello"
+    sw.WriteLine "And"
+    sw.WriteLine "Welcome"
+
+// This text is always added, making the file longer over time
+// if it is not deleted.
+do
+    use sw = File.AppendText path
+    sw.WriteLine "This"
+    sw.WriteLine "is Extra"
+    sw.WriteLine "Text"
+
+// Open the file to read from.
+do
+    use sr = File.OpenText path
+
+    let mutable s = sr.ReadLine()
+
+    while isNull s |> not do
+        printfn $"{s}"
+        s <- sr.ReadLine()
+// </Snippet1>

snippets/fsharp/System.IO/File/AppendText/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="file_appendtext.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.IO/File/Copy/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="program.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.IO/File/Copy/program.fs

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+open System.IO
+
+// <Snippet1>
+let sourceDir = @"c:\current"
+let backupDir = @"c:\archives\2008"
+
+try
+    let picList = Directory.GetFiles(sourceDir, "*.jpg")
+    let txtList = Directory.GetFiles(sourceDir, "*.txt")
+
+    // Copy picture files.
+    for f in picList do
+        // Remove path from the file name.
+        let fName = f.Substring(sourceDir.Length + 1)
+
+        // Use the Path.Combine method to safely append the file name to the path.
+        // Will overwrite if the destination file already exists.
+        File.Copy(Path.Combine(sourceDir, fName), Path.Combine(backupDir, fName), true)
+
+    // Copy text files.
+    for f in txtList do
+        // Remove path from the file name.
+        let fName = f.Substring(sourceDir.Length + 1)
+
+        try
+            // Will not overwrite if the destination file already exists.
+            File.Copy(Path.Combine(sourceDir, fName), Path.Combine(backupDir, fName))
+
+        // Catch exception if the file was already copied.
+        with
+        | :? IOException as copyError -> printfn $"{copyError.Message}"
+
+    // Delete source files that were copied.
+    for f in txtList do
+        File.Delete f
+
+    for f in picList do
+        File.Delete f
+
+// Catch exception if the file was already copied.
+with
+| :? DirectoryNotFoundException as dirNotFound -> printfn $"{dirNotFound.Message}"
+
+// </Snippet1>

snippets/fsharp/System.IO/File/Create/file create1.fs

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+module filecreate1
+
+// <Snippet1>
+open System.IO
+open System.Text
+
+let path = @"c:\temp\MyTest.txt"
+
+// Create the file, or overwrite if the file exists.
+do
+    use fs = File.Create path
+
+    let info =
+        UTF8Encoding(true)
+            .GetBytes "This is some text in the file."
+    // Add some information to the file.
+    fs.Write(info, 0, info.Length)
+
+// Open the stream and read it back.
+do
+    use sr = File.OpenText path
+    let mutable s = sr.ReadLine()
+
+    while isNull s |> not do
+        printfn $"{s}"
+        s <- sr.ReadLine()
+// </Snippet1>