diff --git a/Cargo.lock b/Cargo.lock
index dc36e4c..0485090 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -13,9 +13,9 @@ dependencies = [
 
 [[package]]
 name = "anyhow"
-version = "1.0.51"
+version = "1.0.44"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8b26702f315f53b6071259e15dd9d64528213b44d61de1ec926eca7715d62203"
+checksum = "61604a8f862e1d5c3229fdd78f8b02c68dcf73a4c4b05fd636d12240aaa242c1"
 
 [[package]]
 name = "atty"
@@ -42,9 +42,9 @@ checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
 
 [[package]]
 name = "cc"
-version = "1.0.72"
+version = "1.0.71"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "22a9137b95ea06864e018375b72adfb7db6e6f68cfc8df5a04d00288050485ee"
+checksum = "79c2681d6594606957bbb8631c4b90a7fcaaa72cdb714743a437b156d6a7eedd"
 
 [[package]]
 name = "cfg-if"
@@ -67,9 +67,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "3.0.0-beta.5"
+version = "3.0.0-beta.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "feff3878564edb93745d58cf63e17b63f24142506e7a20c87a5521ed7bfb1d63"
+checksum = "fcd70aa5597dbc42f7217a543f9ef2768b2ef823ba29036072d30e1d88e98406"
 dependencies = [
  "atty",
  "bitflags",
@@ -80,14 +80,14 @@ dependencies = [
  "strsim",
  "termcolor",
  "textwrap",
- "unicase",
+ "vec_map",
 ]
 
 [[package]]
 name = "clap_derive"
-version = "3.0.0-beta.5"
+version = "3.0.0-beta.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8b15c6b4f786ffb6192ffe65a36855bc1fc2444bcd0945ae16748dcd6ed7d0d3"
+checksum = "0b5bb0d655624a0b8770d1c178fb8ffcb1f91cc722cb08f451e3dc72465421ac"
 dependencies = [
  "heck",
  "proc-macro-error",
@@ -157,9 +157,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.108"
+version = "0.2.103"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8521a1b57e76b1ec69af7599e75e38e7b7fad6610f037db8c79b127201b5d119"
+checksum = "dd8f7255a17a627354f321ef0055d63b898c6fb27eff628af4d1b66b7331edf6"
 
 [[package]]
 name = "log"
@@ -233,12 +233,9 @@ dependencies = [
 
 [[package]]
 name = "os_str_bytes"
-version = "4.2.0"
+version = "3.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "addaa943333a514159c80c97ff4a93306530d965d27e139188283cd13e06a799"
-dependencies = [
- "memchr",
-]
+checksum = "6acbef58a60fe69ab50510a55bc8cdd4d6cf2283d27ad338f54cb52747a9cf2d"
 
 [[package]]
 name = "posixmq"
@@ -275,9 +272,9 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.32"
+version = "1.0.29"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ba508cc11742c0dc5c1659771673afbab7a0efab23aa17e854cbab0837ed0b43"
+checksum = "b9f5105d4fdaab20335ca9565e106a5d9b82b6219b5ba735731124ac6711d23d"
 dependencies = [
  "unicode-xid",
 ]
@@ -316,9 +313,9 @@ checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
 
 [[package]]
 name = "syn"
-version = "1.0.82"
+version = "1.0.80"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8daf5dd0bb60cbd4137b1b587d2fc0ae729bc07cf01cd70b36a1ed5ade3b9d59"
+checksum = "d010a1623fbd906d51d650a9916aaefc05ffa0e4053ff7fe601167f3e715d194"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -383,15 +380,6 @@ dependencies = [
  "winapi",
 ]
 
-[[package]]
-name = "unicase"
-version = "2.6.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "50f37be617794602aabbeee0be4f259dc1778fabe05e2d67ee8f79326d5cb4f6"
-dependencies = [
- "version_check",
-]
-
 [[package]]
 name = "unicode-segmentation"
 version = "1.8.0"
@@ -410,6 +398,12 @@ version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8ccb82d61f80a663efe1f787a51b16b5a51e3314d6ac365b08639f52387b33f3"
 
+[[package]]
+name = "vec_map"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1bddf1187be692e79c5ffeab891132dfb0f236ed36a43c7ed39f1165ee20191"
+
 [[package]]
 name = "version_check"
 version = "0.9.3"
diff --git a/Cargo.toml b/Cargo.toml
index f8005b0..b69b952 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "mqrs"
 version = "0.1.1"
 authors = ["finga <mqrs@onders.org>"]
-edition = "2021"
+edition = "2018"
 repository = "https://git.onders.org/finga/mqrs"
 license = "GPL-3.0-or-later"
 readme = "README.md"
diff --git a/src/main.rs b/src/main.rs
index c4b0787..2e01aa6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,10 +1,10 @@
 use anyhow::Result;
-use clap::{crate_authors, crate_version, AppSettings, Parser};
+use clap::{crate_authors, crate_version, AppSettings, Clap};
 
 mod posix;
 mod sysv;
 
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 enum Backend {
     /// Handle POSIX message queues
     #[clap(subcommand)]
@@ -14,7 +14,7 @@ enum Backend {
     Sysv(SysvCommand),
 }
 
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 enum PosixCommand {
     Create(posix::Create),
     Info(posix::Info),
@@ -24,7 +24,7 @@ enum PosixCommand {
     Recv(posix::Recv),
 }
 
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 enum SysvCommand {
     Create(sysv::Create),
     Info(sysv::Info),
@@ -32,7 +32,7 @@ enum SysvCommand {
     Unlink(sysv::Unlink),
 }
 
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 #[clap(
     version = crate_version!(),
     author = crate_authors!(", "),
diff --git a/src/posix/create.rs b/src/posix/create.rs
index cceabde..be4606b 100644
--- a/src/posix/create.rs
+++ b/src/posix/create.rs
@@ -1,11 +1,11 @@
 use anyhow::Result;
-use clap::Parser;
+use clap::Clap;
 use log::{info, log_enabled, Level::Info};
 use posixmq::PosixMq;
 use std::fs;
 
 /// Create a POSIX message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Create {
     /// Permissions (octal) to create the queue with
     #[clap(short, long)]
@@ -40,7 +40,7 @@ impl Create {
         let mq = &mut posixmq::OpenOptions::readonly();
 
         if let Some(m) = &self.mode {
-            mq.mode(u32::from_str_radix(m, 8)?);
+            mq.mode(u32::from_str_radix(&m, 8)?);
         }
 
         mq.max_msg_len(self.msgsize.unwrap_or_else(msgsize_default))
@@ -53,10 +53,10 @@ impl Create {
             let attributes = mq.attributes()?;
 
             info!("Created message queue: {} with attributes msgsize: {}, capacity: {}, current_messages: {}",
-                     self.queue,
-                     attributes.max_msg_len,
-                     attributes.capacity,
-                     attributes.current_messages);
+                     &self.queue,
+                     &attributes.max_msg_len,
+                     &attributes.capacity,
+                     &attributes.current_messages);
         }
 
         Ok(())
diff --git a/src/posix/info.rs b/src/posix/info.rs
index 2a95f6b..abf9641 100644
--- a/src/posix/info.rs
+++ b/src/posix/info.rs
@@ -1,9 +1,9 @@
 use anyhow::Result;
-use clap::Parser;
+use clap::Clap;
 use posixmq::PosixMq;
 
 /// Print information about an existing message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Info {
     /// Name of the queue
     #[clap(value_name = "QUEUE")]
@@ -16,7 +16,7 @@ impl Info {
 
         println!(
             "Message queue: {}, msg_max: {}, msgsize_max: {}, current_messages: {}",
-            self.queue, attrs.capacity, attrs.max_msg_len, attrs.current_messages
+            &self.queue, &attrs.capacity, &attrs.max_msg_len, &attrs.current_messages
         );
 
         Ok(())
diff --git a/src/posix/list.rs b/src/posix/list.rs
index 57fa45d..f9c02b6 100644
--- a/src/posix/list.rs
+++ b/src/posix/list.rs
@@ -1,11 +1,11 @@
 use anyhow::{anyhow, Result};
 use chrono::{DateTime, Local};
-use clap::Parser;
+use clap::Clap;
 use log::warn;
 use std::{fs, os::unix::fs::PermissionsExt};
 
 /// Print a list of existing message queues
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct List {
     /// Show all parameters
     #[clap(short, long)]
diff --git a/src/posix/recv.rs b/src/posix/recv.rs
index c3abb66..6d83cef 100644
--- a/src/posix/recv.rs
+++ b/src/posix/recv.rs
@@ -1,13 +1,13 @@
 use anyhow::Result;
 use chrono::{DateTime, Local};
-use clap::Parser;
+use clap::Clap;
 use humantime::Duration;
 use log::info;
 use posixmq::PosixMq;
 use std::str;
 
 /// Receive and print a message from a message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Recv {
     /// Do not block
     #[clap(short, long)]
diff --git a/src/posix/send.rs b/src/posix/send.rs
index 6dd70de..d6feefc 100644
--- a/src/posix/send.rs
+++ b/src/posix/send.rs
@@ -1,11 +1,11 @@
 use anyhow::Result;
 use chrono::DateTime;
-use clap::Parser;
+use clap::Clap;
 use humantime::Duration;
 use log::info;
 
 /// Send a message to a message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Send {
     /// Set a different priority, priority >= 0
     #[clap(short, long, default_value = "0")]
@@ -38,24 +38,24 @@ impl Send {
         if let Some(timeout) = &self.timeout {
             mq.open(&self.queue)?.send_timeout(
                 self.priority,
-                self.msg.as_bytes(),
+                &self.msg.as_bytes(),
                 *timeout.parse::<Duration>()?,
             )?;
 
-            info!("Sent message: \"{}\" to queue: {}", self.msg, self.queue);
+            info!("Sent message: \"{}\" to queue: {}", &self.msg, &self.queue);
         } else if let Some(deadline) = &self.deadline {
             mq.open(&self.queue)?.send_deadline(
                 self.priority,
-                self.msg.as_bytes(),
+                &self.msg.as_bytes(),
                 DateTime::parse_from_str(deadline, "%Y-%m-%d %H:%M:%S")?.into(),
             )?;
 
-            info!("Sent message: \"{}\" to queue: {}", self.msg, self.queue);
+            info!("Sent message: \"{}\" to queue: {}", &self.msg, &self.queue);
         } else {
             mq.open(&self.queue)?
-                .send(self.priority, self.msg.as_bytes())?;
+                .send(self.priority, &self.msg.as_bytes())?;
 
-            info!("Sent message: \"{}\" to queue: {}", self.msg, self.queue);
+            info!("Sent message: \"{}\" to queue: {}", &self.msg, &self.queue);
         }
 
         Ok(())
diff --git a/src/posix/unlink.rs b/src/posix/unlink.rs
index 75a8bd2..4b89a27 100644
--- a/src/posix/unlink.rs
+++ b/src/posix/unlink.rs
@@ -1,9 +1,9 @@
 use anyhow::Result;
-use clap::Parser;
+use clap::Clap;
 use log::info;
 
 /// Delete a message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Unlink {
     /// Name of the queue
     #[clap(value_name = "QUEUE")]
@@ -14,7 +14,7 @@ impl Unlink {
     pub fn run(&self) -> Result<()> {
         posixmq::remove_queue(&self.queue)?;
 
-        info!("Removed message queue: {}", self.queue);
+        info!("Removed message queue: {}", &self.queue);
 
         Ok(())
     }
diff --git a/src/sysv/create.rs b/src/sysv/create.rs
index 4adad77..e4b03a6 100644
--- a/src/sysv/create.rs
+++ b/src/sysv/create.rs
@@ -1,10 +1,10 @@
 use anyhow::Result;
-use clap::Parser;
+use clap::Clap;
 use log::info;
 use sysvmq::SysvMq;
 
 /// Create a SysV message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Create {
     /// Permissions (octal) to create the queue with (default: 0644)
     #[clap(short, long)]
@@ -19,7 +19,7 @@ impl Create {
         let mut mq = SysvMq::<String>::new();
 
         if let Some(m) = &self.mode {
-            mq.mode(i32::from_str_radix(m, 8)?);
+            mq.mode(i32::from_str_radix(&m, 8)?);
         }
 
         mq.create(self.key)?;
diff --git a/src/sysv/info.rs b/src/sysv/info.rs
index 77d4b3e..42d9fac 100644
--- a/src/sysv/info.rs
+++ b/src/sysv/info.rs
@@ -1,12 +1,12 @@
 use anyhow::Result;
-use clap::Parser;
+use clap::Clap;
 use std::{
     fs::File,
     io::{BufRead, BufReader},
 };
 
 /// Print information about an existing message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Info {
     /// Id of the queue
     #[clap(short, long, required_unless_present_any = &["key"], conflicts_with = "key")]
@@ -28,7 +28,7 @@ impl Info {
     pub fn run(&self) -> Result<()> {
         let mut lines = BufReader::new(File::open("/proc/sysvipc/msg")?).lines();
 
-        print_line(&lines.next().unwrap_or_else(|| Ok(String::new()))?);
+        print_line(&lines.nth(0).unwrap_or(Ok(String::new()))?);
 
         for line in lines {
             let line = line?;
diff --git a/src/sysv/list.rs b/src/sysv/list.rs
index 7c12f16..9f66951 100644
--- a/src/sysv/list.rs
+++ b/src/sysv/list.rs
@@ -1,12 +1,12 @@
 use anyhow::Result;
-use clap::Parser;
+use clap::Clap;
 use std::{
     fs::File,
     io::{BufRead, BufReader},
 };
 
 /// Print a list of existing message queues
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct List {}
 
 impl List {
diff --git a/src/sysv/unlink.rs b/src/sysv/unlink.rs
index 9b4b998..8723d20 100644
--- a/src/sysv/unlink.rs
+++ b/src/sysv/unlink.rs
@@ -1,9 +1,9 @@
 use anyhow::Result;
-use clap::Parser;
+use clap::Clap;
 use log::info;
 
 /// Delete a message queue
-#[derive(Debug, Parser)]
+#[derive(Clap, Debug)]
 pub struct Unlink {
     /// Id of the queue
     #[clap(