init

.gitignore

@@ -0,0 +1,38 @@
+# Compiled binary files
+/target
+
+# Dependency lock file
+Cargo.lock
+
+# IDE files
+.idea
+*.iml
+*.ipr
+*.iws
+.vscode/
+
+# OS generated files
+.DS_Store
+Thumbs.db
+
+# Rust-specific files
+*.rs.bk
+*.rlib
+*.rmeta
+*.d
+*.so
+*.dll
+*.exe
+*.pdb
+
+# Backup files
+*~
+*.bak
+*.swp
+
+# Editor backup files
+*.swo
+
+# Temporary files
+*.tmp
+

Cargo.toml

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+[package]
+name = "header"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+clap = "3.0.0"
+
+[profile.release]
+lto = true
+codegen-units = 1
+strip = true

src/main.rs

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+use clap::{App, Arg};
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::process;
+
+fn main() {
+    let matches = App::new("header")
+        .version("1.0")
+        .author("Your Name")
+        .about("Prints the first line of a file, optionally with field numbers.")
+        .arg(
+            Arg::with_name("delimiter")
+                .short('d')
+                .long("delimiter")
+                .value_name("DELIMITER")
+                .help("Sets the field delimiter")
+                .default_value("\t"),
+        )
+        .arg(
+            Arg::with_name("number")
+                .short('n')
+                .long("number")
+                .help("Show the field number"),
+        )
+        .arg(
+            Arg::with_name("input")
+                .value_name("FILE")
+                .help("Input file to process")
+                .required(true)
+                .index(1),
+        )
+        .get_matches();
+
+    let delimiter = matches.value_of("delimiter").unwrap();
+    let show_number = matches.is_present("number");
+    let input_file = matches.value_of("input").unwrap();
+
+    let file = File::open(input_file).unwrap_or_else(|err| {
+        eprintln!("Error opening file: {}", err);
+        process::exit(1);
+    });
+
+    let reader = BufReader::new(file);
+
+    if let Some(Ok(line)) = reader.lines().next() {
+        let fields: Vec<&str> = line.split(delimiter).collect();
+        for (index, field) in fields.iter().enumerate() {
+            if show_number {
+                println!("{}\t{}", field, index + 1);
+            } else {
+                println!("{}", field);
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write;
+
+    #[test]
+    fn test_main() {
+        let test_input = "field1\tfield2\tfield3\n";
+        let mut test_file = tempfile::NamedTempFile::new().expect("Failed to create temp file");
+        write!(test_file, "{}", test_input).expect("Failed to write to temp file");
+
+        let test_file_path = test_file.path().to_str().unwrap();
+
+        let output = std::process::Command::new(std::env::current_exe().unwrap())
+            .arg("-d")
+            .arg("\t")
+            .arg("-n")
+            .arg(test_file_path)
+            .output()
+            .expect("Failed to execute process");
+
+        assert!(output.status.success());
+        let output_str = String::from_utf8_lossy(&output.stdout);
+        assert_eq!(output_str.trim(), "field1 1\nfield2 2\nfield3 3");
+    }
+}