From: Pádraig Brady <P@draigBrady.com>
Date: Thu, 12 Mar 2026 17:27:00 +0000 (+0000)
Subject: cut: implement -n to avoid outputting partial characters
X-Git-Tag: v9.11~117
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=57110d8bae0637baab050466fad2946b645b51a0;p=thirdparty%2Fcoreutils.git

cut: implement -n to avoid outputting partial characters

Both the i18n patch and FreeBSD/macOS support this option.
They do differ in behavior somewhat as the i18n patch
may output more bytes than requested.

  $ printf '\xc3\xa9b\n' | i18n-cut -n -b1
  é

There is also a bug in the i18n patch with multi-byte
at the start of a line:

  $ printf '\xc3\xa9b\n' | i18n-cut -n -b1-2
  éb

We follow the FreeBSD behavior since it seems more
useful to have -b be a hard limit, rather than a soft limit.
This also reduces the possibility of duplicate character output
with separate cut invocations with non overlapping byte ranges.

* src/cut.c (cut_bytes_no_split): A new function
similar to cut_characters, to handle multi-byte characters
with byte limit semantics.
* tests/cut/cut.pl: Add test cases.
---

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 042173a720..fd0b7edeae 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -6215,7 +6215,10 @@ With @option{-f}, use the first byte of @var{input_delim_byte} as
 the input fields separator (default is TAB).
 
 @optItem{cut,-n,}
-Do not split multi-byte characters (no-op for now).
+@optItemx{cut,--no-partial,}
+With @option{--bytes}, do not split multi-byte characters.
+A byte range must encompass the end of a multi-byte character
+for it to be selected.
 
 @optItem{cut,-s,}
 @optItemx{cut,--only-delimited,}
diff --git a/src/cut.c b/src/cut.c
index 7381395d67..613e2a9ea1 100644
--- a/src/cut.c
+++ b/src/cut.c
@@ -109,6 +109,9 @@ static char output_delimiter_default[MB_LEN_MAX];
 /* True if we have ever read standard input.  */
 static bool have_read_stdin;
 
+/* If true, don't split multibyte characters in byte mode.  */
+static bool no_split;
+
 /* If true, interpret each run of whitespace as one field delimiter.  */
 static bool whitespace_delimited;
 
@@ -135,6 +138,7 @@ static struct option const longopts[] =
   {"characters", required_argument, NULL, 'c'},
   {"fields", required_argument, NULL, 'f'},
   {"delimiter", required_argument, NULL, 'd'},
+  {"no-partial", no_argument, NULL, 'n'},
   {"whitespace-delimited", no_argument, NULL, 'w'},
   {"only-delimited", no_argument, NULL, 's'},
   {"output-delimiter", required_argument, NULL, OUTPUT_DELIMITER_OPTION},
@@ -185,8 +189,8 @@ Print selected parts of lines from each FILE to standard output.\n\
          no delimiter character, unless the -s option is specified\n\
 "));
       oputs (_("\
-  -n\n\
-         (ignored)\n\
+  -n, --no-partial\n\
+         with -b, don't output partial multi-byte characters\n\
 "));
       oputs (_("\
   -s, --only-delimited\n\
@@ -371,6 +375,79 @@ cut_bytes (FILE *stream)
     }
 }
 
+/* Read from STREAM, printing selected bytes without splitting
+   multibyte characters.  */
+
+static void
+cut_bytes_no_split (FILE *stream)
+{
+  uintmax_t byte_idx = 0;
+  bool print_delimiter = false;
+  static char line_in[IO_BUFSIZE];
+  mbbuf_t mbbuf;
+
+  current_rp = frp;
+  mbbuf_init (&mbbuf, line_in, sizeof line_in, stream);
+
+  while (true)
+    {
+      mcel_t g = mbbuf_get_char (&mbbuf);
+
+      if (g.ch == line_delim)
+        {
+          if (putchar (line_delim) < 0)
+            write_error ();
+          byte_idx = 0;
+          print_delimiter = false;
+          current_rp = frp;
+        }
+      else if (g.ch == MBBUF_EOF)
+        {
+          if (byte_idx > 0)
+            {
+              if (putchar (line_delim) < 0)
+                write_error ();
+            }
+          break;
+        }
+      else
+        {
+          bool first_selected_is_range_start = false;
+          bool seen_selected = false;
+          bool suffix_selected = true;
+
+          for (idx_t i = 0; i < g.len; i++)
+            {
+              next_item (&byte_idx);
+              if (print_kth (byte_idx))
+                {
+                  if (!seen_selected)
+                    {
+                      seen_selected = true;
+                      first_selected_is_range_start
+                        = is_range_start_index (byte_idx);
+                    }
+                }
+              else if (seen_selected)
+                suffix_selected = false;
+            }
+
+          if (seen_selected && suffix_selected)
+            {
+              if (output_delimiter_string != output_delimiter_default)
+                {
+                  if (print_delimiter && first_selected_is_range_start)
+                    write_bytes (output_delimiter_string,
+                                 output_delimiter_length);
+                  print_delimiter = true;
+                }
+
+              write_bytes (mbbuf_char_offset (&mbbuf, g), g.len);
+            }
+        }
+    }
+}
+
 /* Read from STREAM, printing to standard output any selected characters.  */
 
 static void
@@ -1042,6 +1119,7 @@ main (int argc, char **argv)
           break;
 
         case 'n':
+          no_split = true;
           break;
 
         case 's':
@@ -1108,7 +1186,8 @@ main (int argc, char **argv)
       unreachable ();
 
     case CUT_MODE_BYTES:
-      cut_stream = cut_bytes;
+      cut_stream = MB_CUR_MAX <= 1 || !no_split
+                   ? cut_bytes : cut_bytes_no_split;
       break;
 
     case CUT_MODE_CHARACTERS:
diff --git a/tests/cut/cut.pl b/tests/cut/cut.pl
index c768124305..905e84c548 100755
--- a/tests/cut/cut.pl
+++ b/tests/cut/cut.pl
@@ -269,6 +269,29 @@ if ($mb_locale ne 'C')
        {ENV => "LC_ALL=$mb_locale"}],
       ['mb-char-5', '-c1-2', {IN=>"\xc3x\n"}, {OUT=>"\xc3x\n"},
        {ENV => "LC_ALL=$mb_locale"}],
+      # Note mb-byte-n-1 and mb-byte-n-4 differ from coreutils-i18n patch,
+      # which outputs a character if any byte is selected.
+      # I.e., the i18n patch may output more bytes that the requested range.
+      # Also mb-byte-n-3 differs from coreutils-i18n patch,
+      # but that looks like a bug in that patch rather than a design choice.
+      ['mb-byte-n-1', qw(-b1 -n), {IN=>"\xc3\xa9x\n"}, {OUT=>"\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
+      ['mb-byte-n-2', qw(-b2 -n), {IN=>"\xc3\xa9x\n"}, {OUT=>"\xc3\xa9\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
+      ['mb-byte-n-3', qw(-b1-2 -n), {IN=>"\xc3\xa9x\n"}, {OUT=>"\xc3\xa9\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
+      ['mb-byte-n-4', qw(-b1,3 -n), {IN=>"\xc3\xa9x\n"}, {OUT=>"x\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
+      ['mb-byte-n-5', qw(-b2-3 -n), {IN=>"\xc3\xa9x\n"}, {OUT=>"\xc3\xa9x\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
+      ['mb-byte-n-6', qw(-b2 -n), {IN=>"\xe2\x82\xacx\n"}, {OUT=>"\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
+      ['mb-byte-n-7', qw(-b3 -n), {IN=>"\xe2\x82\xacx\n"},
+       {OUT=>"\xe2\x82\xac\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
+      ['mb-byte-n-8', qw(-b2-3 -n), {IN=>"\xe2\x82\xacx\n"},
+       {OUT=>"\xe2\x82\xac\n"},
+       {ENV => "LC_ALL=$mb_locale"}],
       ['mb-delim-1', '-d', "\xc3\xa9", '-f2',
        {IN=>"a\xc3\xa9b\xc3\xa9c\n"}, {OUT=>"b\n"},
        {ENV => "LC_ALL=$mb_locale"}],