Add ProcessAsyncEnumerable.FirstAsync, FirstOrDefaultAsync

Author: neuecc

README.md

@@ -48,6 +48,9 @@ await foreach (string item in ProcessX.StartAsync("dotnet --info"))
     Console.WriteLine(item);
 }
 
+// receive string result from stdout.
+var branch = await ProcessX.StartAsync("git branch --show-current").FirstAsync();
+
 // receive buffered result(similar as WaitForExit).
 string[] result = await ProcessX.StartAsync("dotnet --info").ToTask();
 
@@ -260,6 +263,12 @@ StartReadBinaryAsync(string command, string? workingDirectory = null, IDictionar
 StartReadBinaryAsync(string fileName, string? arguments, string? workingDirectory = null, IDictionary<string, string>? environmentVariable = null, Encoding? encoding = null)
 StartReadBinaryAsync(ProcessStartInfo processStartInfo)
 
+// return Task<string>
+FirstAsync(CancellationToken cancellationToken = default)
+
+// return Task<string?>
+FirstOrDefaultAsync(CancellationToken cancellationToken = default)
+
 // return Task<string[]>
 ToTask(CancellationToken cancellationToken = default)
 

sandbox/ConsoleApp/Program.cs

@@ -3,9 +3,16 @@
 
 // ProcessX and C# 9.0 Top level statement; like google/zx.
 
+using Cysharp.Diagnostics;
 using Zx;
 using static Zx.Env;
 
+
+
+var s = await ProcessX.StartAsync("git branch --show-current").FirstAsync();
+System.Console.WriteLine(s);
+
+
 // `await string` execute process like shell
 await "cat package.json | grep name";
 

src/ProcessX/ProcessAsyncEnumerable.cs

@@ -24,6 +24,30 @@ public IAsyncEnumerator<string> GetAsyncEnumerator(CancellationToken cancellatio
             return new ProcessAsyncEnumerator(process, channel, cancellationToken);
         }
 
+        /// <summary>
+        /// Returning first value. If does not return any data, returns empty string.
+        /// </summary>
+        public async Task<string> FirstAsync(CancellationToken cancellationToken = default)
+        {
+            await foreach (var item in this.WithCancellation(cancellationToken).ConfigureAwait(false))
+            {
+                return item;
+            }
+            throw new InvalidOperationException("Process does not return any data.");
+        }
+
+        /// <summary>
+        /// Returning first value or null.
+        /// </summary>
+        public async Task<string?> FirstOrDefaultAsync(CancellationToken cancellationToken = default)
+        {
+            await foreach (var item in this.WithCancellation(cancellationToken).ConfigureAwait(false))
+            {
+                return item;
+            }
+            return default;
+        }
+
         public async Task<string[]> ToTask(CancellationToken cancellationToken = default)
         {
             var list = new List<string>();

src/ProcessX/ProcessX.cs

@@ -120,7 +120,7 @@ public static ProcessAsyncEnumerable StartAsync(ProcessStartInfo processStartInf
             {
                 if (e.Data != null)
                 {
-                    lock (errorList)
+                     lock (errorList)
                     {
                         errorList.Add(e.Data);
                     }