cut: fix "-s" flag to omit blank lines

Using cut with the delimiter flag ("-d") with the "-s" flag to only
output lines containing the delimiter will print blank lines. This is
deviant behavior from cut provided by GNU Coreutils. Blank lines should
be omitted if "-s" is used with "-d".

This change introduces a somewhat naiive, yet efficient solution, where
line length is checked before looping though bytes. If line length is
zero and the "-s" flag is used, the code will jump to parsing the next
line to avoid printing a newline character.

function                                             old     new   delta
cut_main                                            1196    1185     -11

Signed-off-by: Colin McAllister <colinmca242@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/testsuite/cut.tests b/testsuite/cut.tests
index 2458c019c..0b401bc00 100755
--- a/testsuite/cut.tests
+++ b/testsuite/cut.tests
@@ -65,6 +65,15 @@ testing "cut with -d -f( ) -s" "cut -d' ' -f3 -s input && echo yes" "yes\n" "$in
 testing "cut with -d -f(a) -s" "cut -da -f3 -s input" "n\nsium:Jim\n\ncion:Ed\n" "$input" ""
 testing "cut with -d -f(a) -s -n" "cut -da -f3 -s -n input" "n\nsium:Jim\n\ncion:Ed\n" "$input" ""
 
+input="\
+
+foo bar baz
+
+bing bong boop
+
+"
+testing "cut with -d -s omits blank lines" "cut -d' ' -f2 -s input" "bar\nbong\n" "$input" ""
+
 # substitute for awk
 optional FEATURE_CUT_REGEX
 testing "cut -DF" "cut -DF 2,7,5" \