publish writing-files

examples.txt

@@ -54,7 +54,7 @@ URL Parsing
 SHA1 Hashes
 Base64 Encoding
 Reading Files
-# Writing Files
+Writing Files
 # File Operations
 Line Filters
 Command-Line Arguments

examples/reading-files/reading-files.sh

@@ -7,3 +7,5 @@ go
 2 bytes @ 6: go
 2 bytes @ 6: go
 5 bytes: hello
+
+# Next we'll look at writing files.

examples/writing-files/writing-files.go

@@ -1,14 +1,58 @@
+// Writing files in Go follows similar patterns to the
+// ones we saw earlier for reading.
+
 package main
 
-import "os"
+import (
+    "bufio"
+    "fmt"
+    "io/ioutil"
+    "os"
+)
 
-func main() {
-    file, err := os.Create("writing-files.txt")
-    if err != nil {
-        panic(err)
+func check(e error) {
+    if e != nil {
+        panic(e)
     }
-    defer file.Close()
-    file.WriteString("contents\n")
 }
 
-// todo: streaming writes
+func main() {
+
+    // To start, here's how to dump a string (or just
+    // bytes) into a file.
+    d1 := []byte("hello\ngo\n")
+    err := ioutil.WriteFile("/tmp/dat1", d1, 0644)
+    check(err)
+
+    // For more granular writes, open a file for writing.
+    f, err := os.Create("/tmp/dat2")
+    check(err)
+
+    // It's idiomatic to defer a `Close` immediately
+    // after opening a file.
+    defer f.Close()
+
+    // You can `Write` byte slices as you'd expect.
+    d2 := []byte{115, 111, 109, 101, 10}
+    n2, err := f.Write(d2)
+    check(err)
+    fmt.Printf("wrote %d bytes\n", n2)
+
+    // A `WriteString` is also available.
+    n3, err := f.WriteString("writes\n")
+    fmt.Printf("wrote %d bytes\n", n3)
+
+    // Issue a `Sync` to flush writes to stable storage.
+    f.Sync()
+
+    // `bufio` provides buffered writers in addition
+    // to the buffered readers we saw earlier.
+    w := bufio.NewWriter(f)
+    n4, err := w.WriteString("buffered\n")
+    fmt.Printf("wrote %d bytes\n", n4)
+
+    // Use `Flush` to ensure all buffered operations have
+    // been applied to the underlying writer.
+    w.Flush()
+
+}

examples/writing-files/writing-files.sh

@@ -0,0 +1,17 @@
+# Try running the file-writing code.
+$ go run writing-files.go 
+wrote 5 bytes
+wrote 7 bytes
+wrote 9 bytes
+
+# Then check the contents of the written files.
+$ cat /tmp/dat1
+hello
+go
+$ cat /tmp/dat2
+some
+writes
+buffered
+
+# Next we'll look at applying some of the file I/O ideas
+# we've just seen to the `stdin` and `stdout` streams.