Merge pull request #1186 from AndyGauge/file-read-lines

File read lines

Author: marioidival

src/SUMMARY.md

@@ -184,6 +184,7 @@
     - [File I/O](std_misc/file.md)
         - [`open`](std_misc/file/open.md)
         - [`create`](std_misc/file/create.md)
+        - [`read lines`](std_misc/file/read_lines.md)
     - [Child processes](std_misc/process.md)
         - [Pipes](std_misc/process/pipe.md)
         - [Wait](std_misc/process/wait.md)

src/std_misc/file/read_lines.md

@@ -0,0 +1,44 @@
+# Read Lines
+
+The method `lines()` returns an iterator over the lines
+of a file.  
+
+`File::open` expects a generic, `AsRef<Path>`.  That's what
+`read_lines()` expects as input.
+
+```rust,no_run
+use std::fs::File;
+use std::io::{self, BufRead};
+use std::path::Path;
+
+fn main() {
+    // File hosts must exist in current path before this produces output
+    if let Ok(lines) = read_lines("./hosts") {
+        // Consumes the iterator, returns an (Optional) String
+        for line in lines {
+            if let Ok(ip) = line {
+                println!("{}", ip);
+            }      
+        }   
+    }
+}
+
+// The output is wrapped in a Result to allow matching on errors
+// Returns an Iterator to the Reader of the lines of the file.
+fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
+where P: AsRef<Path>, {
+    let file = File::open(filename)?;
+    Ok(io::BufReader::new(file).lines())
+}
+```
+
+Running this program simply prints the lines individually.
+```bash
+$ echo -e "127.0.0.1\n192.168.0.1\n" > hosts
+$ rustc read_lines.rs && ./read_lines
+127.0.0.1
+192.168.0.1
+```
+
+This process is more efficient than creating a `String` in memory
+especially working with larger files.