From 9af435039575fa76dcb710f40d87d3e792e2f6d2 Mon Sep 17 00:00:00 2001
From: Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: Fri, 18 Jul 2025 10:34:28 +0300
Subject: [PATCH v3 1/3] Add trim_file() helper to Utils.pm

The trim_file() function trims lines from a file, either from the head
or the tail, based on the provided direction. It takes how many lines to
trim as a 'line_count' argument but if 'PG_TEST_FILE_TRIM_LINES'
environment variable is set, it overrides the 'line_count'.

Suggested-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAN55FZ1D6KXvjSs7YGsDeadqCxNF3UUhjRAfforzzP0k-cE%3DbA%40mail.gmail.com
---
 src/test/perl/PostgreSQL/Test/Utils.pm | 53 ++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/src/test/perl/PostgreSQL/Test/Utils.pm b/src/test/perl/PostgreSQL/Test/Utils.pm
index 85d36a3171e..42ada64d5b7 100644
--- a/src/test/perl/PostgreSQL/Test/Utils.pm
+++ b/src/test/perl/PostgreSQL/Test/Utils.pm
@@ -68,6 +68,7 @@ our @EXPORT = qw(
   slurp_file
   append_to_file
   string_replace_file
+  trim_file
   check_mode_recursive
   chmod_recursive
   check_pg_config
@@ -590,6 +591,58 @@ sub string_replace_file
 
 =pod
 
+=item trim_file(filename, direction, line_count)
+
+Return lines from the head or tail of given file.
+
+=cut
+
+sub trim_file
+{
+	my ($filename, $direction, $line_count) = @_;
+	my @lines;
+
+	if ($direction ne 'tail' && $direction ne 'head')
+	{
+		die
+		  "trim_file(_, direction, _) direction should be either 'tail' or 'head'.";
+	}
+
+	my $temp_env_var = $ENV{PG_TEST_FILE_TRIM_LINES};
+	if (defined $temp_env_var)
+	{
+		$line_count = $temp_env_var;
+	}
+	if ($line_count <= 0)
+	{
+		return;
+	}
+
+	open my $fh, '<', $filename or die "couldn't open file: $filename\n";
+
+	if ($direction eq 'head')
+	{
+		while (my $line = <$fh>)
+		{
+			push @lines, $line;
+			last if $. == $line_count;
+		}
+	}
+	elsif ($direction eq 'tail')
+	{
+		while (my $line = <$fh>)
+		{
+			push @lines, $line;
+			shift @lines if @lines > $line_count;
+		}
+	}
+
+	close $fh;
+	return @lines;
+}
+
+=pod
+
 =item check_mode_recursive(dir, expected_dir_mode, expected_file_mode, ignore_list)
 
 Check that all file/dir modes in a directory match the expected values,
-- 
2.50.0