fix: handle write errors gracefully instead of panicking on /dev/full

Cargo.toml

@@ -93,6 +93,8 @@ unused_qualifications = "warn"
 all = { level = "warn", priority = -1 }
 cargo = { level = "warn", priority = -1 }
 pedantic = { level = "warn", priority = -1 }
+print_stdout = "warn"                        # restriction: forbid print/println macros
+print_stderr = "warn"                        # restriction: forbid eprint/eprintln macros
 use_self = "warn"                            # nursery lint
 cargo_common_metadata = "allow"              # 3240
 multiple_crate_versions = "allow"            # 2882

src/main.rs

@@ -9,6 +9,7 @@ mod cli;
 mod utils;
 
 use std::env::args_os;
+use std::io::{self, Write};
 
 use bumpalo::Bump;
 use clap::Parser as _;
@@ -45,7 +46,11 @@ fn uu_main() -> Result<()> {
             return Ok(());
         }
     };
-    println!("---\n{ast}");
+    if let Err(e) = writeln!(io::stdout(), "---\n{ast}")
+        && e.kind() != io::ErrorKind::BrokenPipe
+    {
+        exit_err(Some(format!("awk: error writing to standard output: {e}")));
+    }
     dbg!(arena.chunk_capacity());
 
     // for token in lex {

src/utils.rs

@@ -4,6 +4,7 @@
 // files that was distributed with this source code.
 
 use std::fmt::{Debug, Display};
+use std::io::{self, Write};
 use std::panic::{UnwindSafe, catch_unwind, set_hook, take_hook};
 use std::process::exit;
 
@@ -73,7 +74,7 @@ pub fn exit_with(res: Result<Option<impl Into<ExitCode>>, impl Display + Debug>)
 
 pub fn exit_err(err: Option<impl Display + Debug>) -> ! {
     if let Some(err) = err {
-        eprintln!("{err}");
+        let _ = writeln!(io::stderr(), "{err}");
     }
     exit(EXIT_FAILURE)
 }

tests/by-util/test_awk.rs

@@ -14,3 +14,29 @@ fn print_first_field() {
 fn no_args_fails_code_one() {
     ucmd().fails_with_code(1);
 }
+
+// Regression test for issue #5: writing to /dev/full must not panic.
+#[cfg(target_os = "linux")]
+#[test]
+fn write_to_dev_full_does_not_panic() {
+    use std::fs::OpenOptions;
+    use std::process::{Command, Stdio};
+
+    let dev_full = match OpenOptions::new().write(true).open("/dev/full") {
+        Ok(f) => f,
+        Err(_) => return, // /dev/full not available; skip.
+    };
+    let output = Command::new(super::TESTS_BINARY)
+        .arg("BEGIN { print 1 }")
+        .stdout(Stdio::from(dev_full))
+        .stderr(Stdio::piped())
+        .output()
+        .expect("failed to spawn awk");
+    // Must not panic (panic exits with code 2).
+    assert_ne!(output.status.code(), Some(2));
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        !stderr.contains("panicked"),
+        "awk panicked on write to /dev/full: stderr={stderr}"
+    );
+}