nl: support a negative --line-increment

* src/nl.c (main): Allow -i to accept down to INTMAX_MIN.
* tests/misc/nl.sh: Add test cases.
* NEWS: Mention the new feature.

4 files changed, 17 insertions, 1 deletions

diff --git a/NEWS b/NEWS
index 61b711611..7cf15498c 100644
--- a/NEWS
+++ b/NEWS
@@ -36,6 +36,8 @@ GNU coreutils NEWS                                    -*- outline -*-
   ls --classify now supports the "always", "auto", or "never" flags,
   to support only outputting classifier characters if connected to a tty.
 
+  nl --line-increment can now take a negative number to decrement the count.
+
 ** Improvements
 
   stat and tail now know about the "vboxsf" file system type.
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index a55514d59..8d9320ca2 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -1867,6 +1867,7 @@ Analogous to @option{--body-numbering}.
 @opindex -i
 @opindex --line-increment
 Increment line numbers by @var{number} (default 1).
+@var{number} can be negative to decrement.
 
 @item -l @var{number}
 @itemx --join-blank-lines=@var{number}
@@ -1916,6 +1917,7 @@ Separate the line number from the text line in the output with
 @opindex -v
 @opindex --starting-line-number
 Set the initial line number on each logical page to @var{number} (default 1).
+The starting @var{number} can be negative.
 
 @item -w @var{number}
 @itemx --number-width=@var{number}
diff --git a/src/nl.c b/src/nl.c
index 154131f36..959909f05 100644
--- a/src/nl.c
+++ b/src/nl.c
@@ -521,7 +521,7 @@ main (int argc, char **argv)
                                              0);
           break;
         case 'i':
-          page_incr = xdectoimax (optarg, 1, INTMAX_MAX, "",
+          page_incr = xdectoimax (optarg, INTMAX_MIN, INTMAX_MAX, "",
                                   _("invalid line number increment"), 0);
           break;
         case 'p':
diff --git a/tests/misc/nl.sh b/tests/misc/nl.sh
index c134a9896..fd9c5326c 100755
--- a/tests/misc/nl.sh
+++ b/tests/misc/nl.sh
@@ -67,4 +67,16 @@ EOF
 compare exp out || fail=1
 returns_ 1 nl -p -v$INTMAX_MAX in.txt > out || fail=1
 
+# Test negative iteration
+returns_ 1 nl -i$INTMAX_UFLOW /dev/null || fail=1
+printf '%s\n' a b > in.txt || framework_failure_
+nl -v$INTMAX_MAX -i$INTMAX_MIN in.txt > out || fail=1
+cat <<EOF > exp
+$INTMAX_MAX	a
+    -1	b
+EOF
+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
+
 Exit $fail