grep --ignore-case --only

Question

grep fails when using both --ignore-case and --only-match options  Example     echo  abc    grep -io abc abc   echo  ABC    grep -io abc      But    echo  abc    grep -i abc abc   echo  ABC    grep -i abc ABC   According to man page       -o  --only-matching           Show only the part of a matching line that matches PATTERN     -i  --ignore-case           Ignore case distinctions in both the PATTERN and the input files     Is it a bug of grep or I didn t get the map page   I am using Mac OS X 10 6 8 and     grep --version grep  GNU grep  2 5 1   Found this link  http   lists gnu org archive html bug-gnu-utils 2003-11 msg00040 html  Of course it is possible to use workaround like grep -o  aA  bB  cC   but this doesn t seem to be a good option

User · Answer

It should be a problem in your version of grep.

Your test cases are working correctly here on my machine:

$ echo "abc" | grep -io abc
abc
$ echo "ABC" | grep -io abc
ABC

And my version is:

$ grep --version
grep (GNU grep) 2.10

User · Answer

I d suggest that the -i means it does match  ABC   but the difference is in the output  -i doesn t manipulate the input  so it won t change  ABC  to  abc  because you specified  abc  as the pattern  -o says it only shows the part of the output that matches the pattern specified  it doesn t say about matching input    The output of echo  ABC    grep -i abc is ABC  the -o shows output matching  abc  so nothing shows   Naos   mattlacey  echo  ABC    grep -i abc   grep -o abc Naos   mattlacey  echo  ABC    grep -i abc   grep -o ABC ABC

User · Answer

This is a known bug on the initial 2 5 1  and has been fixed in early 2007  Redhat 2 5 1-5  according to the bug reports  Unfortunately Apple is still using 2 5 1 even on Mac OS X 10 7 2   You could get a newer version via Homebrew  3 0  or MacPorts  2 26  or fink  3 0-1      Edit  Apparently it has been fixed on OS X 10 11  or maybe earlier   even though the grep version reported is still 2 5 1

User · Answer

If your grep -i does not work then try using tr command to convert the the output of your file to lower case and then pipe it into standard grep with whatever you are looking for   it sounds complicated but the actual command which I have provided for you is not      Notice the tr command does not change the content of your original file  it just converts it just before it feeds it into grep    1 here is how you can do this on a file   tr    upper       lower     lt your file txt grep what ever you are searching in lower case   2 or in your case if you are just echoing something  echo  ABC  tr    upper       lower      grep abc

[regex] grep --ignore-case --only

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