added the --dry-run option for testing.

t/help.txt

@@ -147,3 +147,5 @@ Options directly inherited from nginx
 
   --with-openssl=DIR                 set path to OpenSSL library sources
   --with-openssl-opt=OPTIONS         set additional options for OpenSSL building
+
+  --dry-run                          dry running the configure, for testing only

t/sanity.t

@@ -1,7 +1,7 @@
 use strict;
 use warnings;
 
-use Test::More tests => 1;
+use Test::More tests => 2;
 use Text::Diff;
 
 sub shell (@);
@@ -13,19 +13,37 @@ chomp $ver;
 #shell "make";
 
 cd "ngx_openresty-$ver";
-shell "./configure --help > help.txt";
 
-open my $in, "help.txt" or
-    die "Cannot open help.txt for reading: $!\n";
-my $got = do { local $/; <$in> };
-close $in;
+{
+    shell "./configure --help > help.txt 2>&1";
 
-open $in, "../t/help.txt" or
-    die "Cannot open ../t/help.txt for reading: $!\n";
-my $expected = do { local $/; <$in> };
-close $in;
+    open my $in, "help.txt" or
+        die "Cannot open help.txt for reading: $!\n";
+    my $got = do { local $/; <$in> };
+    close $in;
 
-is_diff($got, $expected, "--help ok");
+    open $in, "../t/help.txt" or
+        die "Cannot open ../t/help.txt for reading: $!\n";
+    my $expected = do { local $/; <$in> };
+    close $in;
+
+    is_diff($got, $expected, "--help ok");
+}
+
+{
+    shell "./configure --dry-run > default.txt 2>&1";
+    open my $in, "default.txt" or
+        die "Cannot open default.txt for reading: $!\n";
+    my $got = do { local $/; <$in> };
+    close $in;
+
+    open $in, "../t/default.txt" or
+        die "Cannot open ../t/default.txt for reading: $!\n";
+    my $expected = do { local $/; <$in> };
+    close $in;
+
+    is_diff($got, $expected, "default configure ok");
+}
 
 sub shell (@) {
     print "@_\n";

util/configure

@@ -62,9 +62,15 @@ my $with_resty_mods_regex;
 
 my $prefix = '/usr/local/openresty';
 my %resty_opts;
+my $dry_run;
 
 my @ngx_opts;
 for my $opt (@ARGV) {
+    if ($opt eq '--dry-run') {
+        $dry_run = 1;
+        next;
+    }
+
     if ($opt =~ /^--prefix=(.*)/) {
         $prefix = $1;
 
@@ -119,12 +125,13 @@ my $ngx_prefix = "$prefix/nginx";
 my $cmd = "./configure --prefix=$ngx_prefix"
     . " --with-ld-opt='-Wl,-rpath=$ngx_prefix/lib'"
     . build_resty_opts(\%resty_opts)
-    . " " . join(" ", @ngx_opts);
+    . (@ngx_opts ? " " . join(" ", @ngx_opts) : "");
    ;
 
-warn $cmd;
-
-exit 0;
+if ($dry_run) {
+    print "$cmd\n";
+    exit 0;
+}
 
 shell $cmd;
 
@@ -183,6 +190,8 @@ sub build_resty_opts {
     } else {
         $opts_line .= " --with-cc-opt='-O2'";
     }
+
+    return $opts_line;
 }
 
 sub usage ($) {
@@ -370,6 +379,8 @@ Options directly inherited from nginx
 
   --with-openssl=DIR                 set path to OpenSSL library sources
   --with-openssl-opt=OPTIONS         set additional options for OpenSSL building
+
+  --dry-run                          dry running the configure, for testing only
 _EOC_
 
     if ($retval == 0) {