unexpected results for: grep -oi

[Ferdinand Beljaars]

Hello,

I ran into some unexpected behaviour for GNU grep version 2.5.1 when combining 
option -o and -i.
If I have read the manual page well, option -o is supposed to make grep print 
only the matching pattern(s)  for some matching expression in the input. When 
adding option -i I would expect this to happen whatever case the expression 
and input happen to be in.

Three illustrative examples from a shell command line:
1)
> echo "
line one
Line Two
line three
line four" | grep -io line 

gives:
line
line
line
>

2)
> echo "
line one
Line Two
line three
line four" | grep -io Line

gives:
Line
>

What is really going on becomes more clear when adding option -n

3)
> echo "
line one
Line Two
line three
line four" | grep -ion Line

gives:
2:3:Line
4:5:>

All lines indeed have a matching pattern due to -i which is confirmed with -n, 
but grep clearly fails to print the matching pattern and even a newline 
character for all non exact matches. 
This gives unpredictable and unusable results.

with kind regards,
Ferdinand Beljaars

address@hidden