grep-2.5.1: bugs with "--only-matching"

[Julian Foad]

grep 2.5.1: bugs with "--only-matching" ("-o"):

1. For a case-insensitive match (with "-i"), when the case does not in fact match, 
"-o" displays empty text, and not even a newline after it (so also messes up the output 
of line numbers or file names).

2. It only displays the line number (-n) or file name (-H) for the first match on a line. 
 The output of subsequent matches is at least inconvenient for further processing (with 
"sort" etc.) and can also be ambiguous because anything that looks like a 
requested line number or file name might instead be part of the matched text.

3. The end of a previous match is mistaken for the start of a new line, matching 
"^".


Reproduction script, showing the output with and without "-o":
[[[
#!/bin/bash
# Demonstrate bugs in "-o" ("--only-matching") option of GNU Grep 2.5.1
grep --version | head -1
TEXT="word
WORD
WORD_WORD
"
set -v

# Bug: Displays empty text, and no newline, for a match that requires "-i".
# Bug: Only displays the line (-n) or file name (-H) for the first match on a 
line.
echo "$TEXT" | grep -ni  WORD
echo "$TEXT" | grep -nio WORD

# Bug: End of a previous match is mistaken for the start of a new line.
echo "$TEXT" | grep -n  "^WORD_*"
echo "$TEXT" | grep -no "^WORD_*"
]]]


This is the output that I get from that script:
[[[
grep (GNU grep) 2.5.1

# Bug: Displays empty text, and no newline, for a match that requires "-i".
# Bug: Only displays the line (-n) or file name (-H) for the first match on a 
line.
echo "$TEXT" | grep -ni  WORD
1:word
2:WORD
3:WORD_WORD
echo "$TEXT" | grep -nio WORD
1:2:WORD
3:WORD
WORD

# Bug: End of a previous match is mistaken for the start of a new line.
echo "$TEXT" | grep -n  "^WORD_*"
2:WORD
3:WORD_WORD
echo "$TEXT" | grep -no "^WORD_*"
2:WORD
3:WORD_
WORD
]]]


This is the output that I expect:
[[[
grep (GNU grep) 2.5.1

# Bug: Displays empty text, and no newline, for a match that requires "-i".
# Bug: Only displays the line (-n) or file name (-H) for the first match on a 
line.
echo "$TEXT" | grep -ni  WORD
1:word
2:WORD
3:WORD_WORD
echo "$TEXT" | grep -nio WORD
1:word
2:WORD
3:WORD
3:WORD

# Bug: End of a previous match is mistaken for the start of a new line.
echo "$TEXT" | grep -n  "^WORD_*"
2:WORD
3:WORD_WORD
echo "$TEXT" | grep -no "^WORD_*"
2:WORD
3:WORD_
]]]

- Julian