doc: mention the GNU extensions to nl --section-delimiter

* doc/coreutils.texi (nl invocation): Mention the GNU extensions
of allowing arbitrary length and empty delimiter strings.
* src/nl.c (usage): Likewise.
* tests/misc/nl.sh: Add test cases for the GNU extensions.

3 files changed, 29 insertions, 4 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 5ac3745bd..df0655c20 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -1805,9 +1805,9 @@ start of body;
 start of footer.
 @end table
 
-The two characters from which these strings are made can be changed from
-@samp{\} and @samp{:} via options (see below), but the pattern and
-length of each string cannot be changed.
+The characters from which these strings are made can be changed from
+@samp{\} and @samp{:} via options (see below), but the pattern
+of each string cannot be changed.
 
 A section delimiter is replaced by an empty line on output.  Any text
 that comes before the first section delimiter string in the input file
@@ -1847,6 +1847,9 @@ expression @var{bre}.
 @cindex section delimiters of pages
 Set the section delimiter characters to @var{cd}; default is
 @samp{\:}.  If only @var{c} is given, the second remains @samp{:}.
+As a GNU extension more than two characters can be specified,
+and also if @var{cd} is empty (@option{-d ''}), then section
+matching is disabled.
 (Remember to protect @samp{\} or other metacharacters from shell
 expansion with quotes or extra backslashes.)
 
diff --git a/src/nl.c b/src/nl.c
index a1b38a7e2..23219b609 100644
--- a/src/nl.c
+++ b/src/nl.c
@@ -211,7 +211,9 @@ Write each FILE to standard output, with line numbers added.\n\
 Default options are: -bt -d'\\:' -fn -hn -i1 -l1 -n'rn' -s<TAB> -v1 -w6\n\
 \n\
 CC are two delimiter characters used to construct logical page delimiters;\n\
-a missing second character implies ':'.\n\
+a missing second character implies ':'.  As a GNU extension one can specify\n\
+more than two characters, and also specifying the empty string (-d '')\n\
+disables section matching.\n\
 "), stdout);
       fputs (_("\
 \n\
diff --git a/tests/misc/nl.sh b/tests/misc/nl.sh
index fd9c5326c..0d57f3443 100755
--- a/tests/misc/nl.sh
+++ b/tests/misc/nl.sh
@@ -79,4 +79,24 @@ compare exp out || fail=1
 printf '%s\n' a b c > in.txt || framework_failure_
 returns_ 1 nl -v$INTMAX_MAX -i$INTMAX_MIN in.txt > out || fail=1
 
+# Test GNU extension to --section-delimiter, of disabling section matching
+printf '%s\n' a '\:\:' c > in.txt || framework_failure_
+nl -d '' in.txt > out || fail=1
+cat <<\EOF > exp
+     1	a
+     2	\:\:
+     3	c
+EOF
+compare exp out || fail=1
+
+# Test GNU extension to --section-delimiter, of supporting strings longer than 2
+printf '%s\n' a foofoo c > in.txt || framework_failure_
+nl -d 'foo' in.txt > out || fail=1
+cat <<EOF > exp
+     1	a
+
+     1	c
+EOF
+compare exp out || fail=1
+
 Exit $fail