Various additions and improvements

src/builtin/shift.rs

@@ -0,0 +1,35 @@
+use crate::{jobs::{ChildProc, JobBldr}, libsh::error::{ErrSpan, ShErr, ShErrKind, ShResult}, parse::{execute::prepare_argv, NdRule, Node}, prelude::*, state::write_vars};
+
+pub fn shift(node: Node, job: &mut JobBldr) -> ShResult<()> {
+	let NdRule::Command { assignments: _, argv } = node.class else {
+		unreachable!()
+	};
+
+	let child_pgid = if let Some(pgid) = job.pgid() {
+		pgid
+	} else {
+		job.set_pgid(Pid::this());
+		Pid::this()
+	};
+	let child = ChildProc::new(Pid::this(), Some("shift"), Some(child_pgid))?;
+	job.push_child(child);
+
+	let mut argv = prepare_argv(argv).into_iter().skip(1);
+
+	if let Some((arg,span)) = argv.next() {
+		let Ok(count) = arg.parse::<usize>() else {
+			return Err(
+				ShErr::full(
+					ShErrKind::ExecFail,
+					"Expected a number in shift args",
+					span.into()
+				)
+			)
+		};
+		for _ in 0..count {
+			write_vars(|v| v.fpop_arg());
+		}
+	}
+
+	Ok(())
+}