From f6e8218a332933d1a6c34421c8a1638cd726c7b4 Mon Sep 17 00:00:00 2001
From: John Ankarstrom <john@ankarstrom.se>
Date: Tue, 6 Jul 2021 16:45:30 +0200
Subject: Add 'build' script

---
 build | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100755 build

diff --git a/build b/build
new file mode 100755
index 0000000..b6d3653
--- /dev/null
+++ b/build
@@ -0,0 +1,103 @@
+#!/usr/bin/perl
+
+# build -- process and act on embedded build instructions
+
+use strict;
+use warnings;
+
+# parse arguments
+
+my ($debug, $fork) = (0, 0);
+my $usage = "usage: $0 [-dddf] file [...]\n";
+
+while (@ARGV and ($_ = $ARGV[0]) =~ /^-/) {
+	shift @ARGV;
+	last if $_ eq '--';
+	$debug++ for /(d)/g;
+	$fork++ if /f/;
+	die $usage if /[^-df]/;
+}
+
+die $usage if not @ARGV;
+
+# find build line(s) in each file
+
+my $i;
+for my $file (@ARGV) {
+	my ($cmd, $target, @deps);
+	open my $f, '<', $file or die "could not open $file: $!\n";
+	$i = 1;
+	while (<$f>) {
+		if (not $cmd and m{
+			^ .*
+			(?: (?:build|generate) \s+ (?:it \s+)? with
+			  | (?:built|generated) \s+ with
+			  | the \s+ command
+			  | run(?:ning)?
+			  | issu(?:e|ing)
+			) \s+
+			(.+?) \s* (?: > \s* (.+?))? \.? \s*
+			(?:\*/)? \s* $
+		}x) {
+			warn "$file build line: $_" if $debug > 2;
+			$cmd = $1;
+			$target = $2;
+		}
+		elsif (not @deps and m{
+			^ .*
+			(?: depends \s+ on
+			  | dependent \s+ on
+			) \s+
+			(?: the \s+ files? \s+ )?
+			(.+?) \.? \s*
+			(?:\*/)? \s* $
+		}x) {
+			warn "$file dependency line: $_" if $debug > 2;
+			push @deps, $_ for split /,?\s+/, $1;
+			if ($deps[-2] eq 'and') {
+				$deps[-2] = $deps[-1];
+				pop @deps;
+			}
+		}
+		last if ++$i > 20;
+	}
+	warn "$file dependencies: @deps\n" if $debug > 1;
+	build($file, $cmd, $target, @deps) if $cmd;
+	warn "$file: no build line found\n" if not $cmd;
+}
+
+# build target according to build line
+
+sub build {
+	my ($source, $cmd, $target, @deps) = @_;
+	my $m = (stat$target)[9];
+
+	if (! -e $target) {
+		warn "$source: building because $target does not exist\n"
+			if $debug;
+		goto update;
+	}
+
+	for ($source, @deps) {
+		if (! -e $_) {
+			warn "$source: non-existent dependency '$_'\n";
+			next;
+		}
+		if ($m < (stat$_)[9]) {
+			warn "$source: building because $_ is modified\n"
+				if $debug;
+			goto update;
+		}
+	}
+	warn "$source: $target already up-to-date\n";
+	return;
+
+update:
+	warn "$source: $cmd > $target\n";
+	if ($fork) {
+		exec('/bin/sh', '-c', "$cmd > $target") if fork() == 0;
+	} else {
+		system("$cmd > $target");
+	}
+	return;
+}
-- 
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