Don't print welcome message when a value is piped

Cargo.lock

@@ -18,6 +18,17 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "atty"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9b39be18770d11421cdb1b9947a45dd3f37e93092cbf377614828a319d5fee8"
+dependencies = [
+ "hermit-abi",
+ "libc",
+ "winapi",
+]
+
 [[package]]
 name = "az"
 version = "1.0.0"
@@ -116,6 +127,15 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "hermit-abi"
+version = "0.1.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "322f4de77956e22ed0e5032c359a0f1273f1f7f0d79bfa3b8ffbc730d7fbcc5c"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "js-sys"
 version = "0.3.46"
@@ -142,6 +162,7 @@ name = "kalk_cli"
 version = "0.5.3"
 dependencies = [
  "ansi_term",
+ "atty",
  "kalk",
  "lazy_static",
  "regex",

kalk_cli/Cargo.toml

@@ -22,6 +22,7 @@ lazy_static = "1.4.0"
 regex = "1"
 rustyline = "7.1.0"
 seahorse = "1.1.1"
+atty = "0.2.14"
 
 [target.'cfg(windows)'.build-dependencies]
 winres = "0.1"

kalk_cli/src/repl.rs

@@ -24,11 +24,15 @@ pub fn start(mut parser: &mut parser::Context, precision: u32) {
         highlighter: LineHighlighter {},
         validator: MatchingBracketValidator::new(),
     }));
+
+    // If in tty, print the welcome message
+    if atty::is(atty::Stream::Stdin) && atty::is(atty::Stream::Stdout) {
         println!("kalk");
         println!(
             "{}",
             ansi_term::Color::Fixed(246).paint("Type 'help' for instructions.")
         );
+    }
 
     loop {
         let prompt = if cfg!(windows) {