Implement info command for SysV IPC mqs

The `list` command was refactored a little bit as well and the man
page and readme were updated.

src/sysv/info.rs

@@ -0,0 +1,53 @@
+use anyhow::Result;
+use clap::Clap;
+use std::{
+    fs::File,
+    io::{BufRead, BufReader},
+};
+
+/// Print information about an existing message queue
+#[derive(Clap, Debug)]
+pub struct Info {
+    /// Id of the queue
+    #[clap(short, long, required_unless_present_any = &["key"], conflicts_with = "key")]
+    id: Option<i32>,
+    /// Key of the queue
+    #[clap(short, long, required_unless_present_any = &["id"], conflicts_with = "id")]
+    key: Option<i32>,
+}
+
+fn print_line(line: &str) {
+    for field in line.split_whitespace().collect::<Vec<&str>>() {
+        print!("{0: <10}", field);
+    }
+
+    println!();
+}
+
+impl Info {
+    pub fn run(&self) -> Result<()> {
+        let mut lines = BufReader::new(File::open("/proc/sysvipc/msg")?).lines();
+
+        print_line(&lines.nth(0).unwrap_or(Ok(String::new()))?);
+
+        for line in lines {
+            let line = line?;
+
+            if let Some(id) = self.id {
+                if id == line.split_whitespace().collect::<Vec<&str>>()[1].parse::<i32>()? {
+                    print_line(&line);
+
+                    break;
+                }
+            } else if let Some(key) = self.key {
+                if key == line.split_whitespace().collect::<Vec<&str>>()[0].parse::<i32>()? {
+                    print_line(&line);
+
+                    break;
+                }
+            }
+        }
+
+        Ok(())
+    }
+}