grcat: add grcat command for gawk library routines

Cargo.toml

@@ -8,6 +8,13 @@ license.workspace = true
 name = "awk"
 path = "src/main.rs"
 
+[[bin]]
+name = "grcat"
+path = "src/bin/grcat.rs"
+
+[target.'cfg(unix)'.dependencies]
+rustix = { version = "1.1.4", features = ["fs"] }
+
 [workspace.package]
 version = "0.1.0"
 license = "MIT OR Apache-2.0"

src/bin/grcat.rs

@@ -0,0 +1,47 @@
+// This file is part of the uutils awk package.
+//
+// For the full copyright and license information, please view the LICENSE
+// files that was distributed with this source code.
+
+//! Dump the group database in `/etc/group` format for gawk library routines.
+//!
+//! Based on the program from the GNU Awk User's Guide (public domain).
+//! <https://www.gnu.org/software/gawk/manual/html_node/Group-Functions.html>
+
+use std::{
+    io::{self, Write},
+    process,
+};
+
+#[cfg(unix)]
+const GROUP_DB: &str = "/etc/group";
+
+fn main() {
+    #[cfg(unix)]
+    {
+        if let Err(err) = run()
+            && err.kind() != io::ErrorKind::BrokenPipe
+        {
+            let _ = writeln!(io::stderr(), "grcat: {err}");
+            process::exit(1);
+        }
+    }
+    #[cfg(not(unix))]
+    {
+        let _ = writeln!(io::stderr(), "grcat: not supported on this platform");
+        process::exit(1);
+    }
+}
+
+#[cfg(unix)]
+fn run() -> io::Result<()> {
+    use rustix::fs::{Mode, OFlags, open};
+    use std::fs::File;
+
+    let fd = open(GROUP_DB, OFlags::RDONLY, Mode::empty())
+        .map_err(|err| io::Error::from_raw_os_error(err.raw_os_error()))?;
+    let mut input = File::from(fd);
+    let mut out = io::stdout().lock();
+    io::copy(&mut input, &mut out)?;
+    Ok(())
+}

tests/grcat.rs

@@ -0,0 +1,75 @@
+// This file is part of the uutils awk package.
+//
+// For the full copyright and license information, please view the LICENSE
+// files that was distributed with this source code.
+
+#[cfg_attr(
+    not(target_os = "linux"),
+    ignore = "grcat tests require Linux NSS via getent"
+)]
+#[test]
+fn grcat_outputs_group_database_format() {
+    use std::process::Command;
+
+    let output = Command::new(env!("CARGO_BIN_EXE_grcat"))
+        .output()
+        .expect("failed to run grcat");
+
+    assert!(
+        output.status.success(),
+        "grcat failed: stderr={}",
+        String::from_utf8_lossy(&output.stderr)
+    );
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(
+        !stdout.is_empty(),
+        "grcat produced no output; group database may be unavailable in this environment"
+    );
+
+    for line in stdout.lines().filter(|line| !line.is_empty()) {
+        let fields: Vec<&str> = line.split(':').collect();
+        assert!(
+            fields.len() >= 4,
+            "expected at least 4 colon-separated fields, got {} in line: {line}",
+            fields.len()
+        );
+        assert!(
+            fields[2].chars().all(|ch| ch.is_ascii_digit()),
+            "expected numeric gid in line: {line}"
+        );
+    }
+}
+
+// Regression test for gawk compatibility: grcat must match the group database
+// format consumed by gawk library routines (see group.awk).
+#[cfg_attr(
+    not(target_os = "linux"),
+    ignore = "grcat tests require Linux NSS via getent"
+)]
+#[test]
+fn grcat_matches_getent_group() {
+    use std::process::Command;
+
+    let getent = Command::new("getent")
+        .arg("group")
+        .output()
+        .expect("failed to run getent");
+    if !getent.status.success() {
+        return;
+    }
+
+    let grcat = Command::new(env!("CARGO_BIN_EXE_grcat"))
+        .output()
+        .expect("failed to run grcat");
+    assert!(
+        grcat.status.success(),
+        "grcat failed: stderr={}",
+        String::from_utf8_lossy(&grcat.stderr)
+    );
+
+    assert_eq!(
+        getent.stdout, grcat.stdout,
+        "grcat output should match getent group"
+    );
+}