[SOLVED] Why this grep command with regular expressions not working on my system?

Andrew Dufresne · 09-30-2009, 10:00 AM

Hi,

Well, actually I have a problem with a text file, test.txt.

Quote:

#test.txt
odsdsdoddf112 test1_for_grep
dad23392eeedJ test2 for grep
Hello World test
garbage

I am trying to find all those words that have a space after them. Each line have more than one such words, but I only want the first one. In other words grep should stop at first match on a line and then proceed to next line.

Question 1
What will you suggest? How can I solve this problem? I only want to use grep and no other tool like gawk.

Question 2
I asked this question here and I was told to use

Quote:

grep -Eo "^[[:alnum:]]+[[:blank:]]" test.txt

But this didn't gave me correct result. My output is

Quote:

odsdsdoddf112
dad23392eeedJ
test2
for
Hello
World

Quite contrary, correct result will be

Quote:

odsdsdoddf112
dad23392eeedJ
Hello

People there say that they are getting correct result. But the expression is not working for me. I have tried it on two Linux systems and got the same wrong result.

Why is it so? Those regular expressions are working for them, but in my case it fails.
What could be the reason? Any idea or help will be greatly appreciated.

Question 3
I have used

Quote:

grep -o ^[[:alnum:]]* test.txt
grep -Eo ^[[:alnum:]]+ test.txt

and this time I got

Quote:

odsdsdoddf112
dad23392eeedJ
Hello
garbage

But clearly, last entry 'garbage' doesn't belong here because it doesn't have a space after it. Which expression should I add here to get correct result?

Any ideas or suggestions are welcome.

Regards

SharpyWarpy · 09-30-2009, 10:24 AM

Enter the following command and post results:
alias
OR try this:
/
before your "grep" command. I'm thinking the grep command might be aliased with some conflicting option(s).

Andrew Dufresne · 09-30-2009, 10:43 AM

Thanks SharpyWarpy for responding to my post.

Quote:

Originally Posted by SharpyWarpy

Enter the following command and post results:
alias

Here is the output

Quote:

$ alias grep
bash: alias: grep: not found
$

Quote:

Originally Posted by SharpyWarpy

OR try this:
/
before your "grep" command. I'm thinking the grep command might be aliased with some conflicting option(s).

I am not sure that I understand this point. Anyway, this is what I did

Quote:

$ /grep -Eo "^[[:alnum:]]+[[:blank:]]" test.txt
bash: /grep: No such file or directory
$ / grep -Eo "^[[:alnum:]]+[[:blank:]]" test.txt
bash: /: is a directory
$

SharpyWarpy · 09-30-2009, 06:31 PM

I meant a backward slash, \ , not a forward slash.
\grep ....
Very sorry for that.

chrism01 · 09-30-2009, 06:55 PM

The \ is to try and escape any aliases etc; you could try just giving the absolute path eg /usr/bin/grep
Unfortunately I don't have a Linux avail right now, and the Solaris grep doesn't recognise those options, so I can't help.

Andrew Dufresne · 09-30-2009, 09:04 PM

Thanks guys for replying.

Quote:

Originally Posted by SharpyWarpy

I meant a backward slash, \ , not a forward slash.
\grep ....
Very sorry for that.

No need to apologize, no big deal.

Quote:

Originally Posted by chrism01

The \ is to try and escape any aliases etc; you could try just giving the absolute path eg /usr/bin/grep

Here is the output :

Quote:

$ /bin/grep -Eo "^[[:alnum:]]+[[:blank:]]" test.txt
odsdsdoddf112
dad23392eeedJ
test2
for
Hello
World
$ \grep -Eo "^[[:alnum:]]+[[:blank:]]" test.txt
odsdsdoddf112
dad23392eeedJ
test2
for
Hello
World
$ grep -Eo "^[[:alnum:]]+[[:blank:]]" test.txt
odsdsdoddf112
dad23392eeedJ
test2
for
Hello
World
$

As you can see, in every case, result is same and incorrect.

Well, what to do now?

Kenhelm · 09-30-2009, 09:32 PM

I get different output according to which version of grep I use.

Code:

lines='
odsdsdoddf112 test1_for_grep
dad23392eeedJ test2 for grep
Hello World test
garbage'

# Using grep version 2.5.1(PCLinuxOS2009.2 and Mandriva2006)
echo "$lines" | grep -Eo "^[[:alnum:]]+[[:blank:]]"
odsdsdoddf112
dad23392eeedJ
test2
for
Hello
World

# Using grep version 2.5.3(Puppy4.20) and 2.5.4(Mandriva2009.0)
echo "$lines" | grep -Eo "^[[:alnum:]]+[[:blank:]]"
odsdsdoddf112
dad23392eeedJ
Hello

It looks as though there is a bug in 'grep -o' version 2.5.1
The 'Beginning-of-line' which is matched by '^' seems to get placed after the last matched sub-string before the next match attempt. So '^' can end up matching positions in the middle of the line.
e.g. (using grep version 2.5.1)

Code:

echo "abcdefghi" | grep -o '^...'
abc
def
ghi               # Output should have been only 'abc'

# It's not that '^' is just being ignored
echo "ab" | grep -o '^b'
            # No output,  '^' has worked.

pixellany · 09-30-2009, 10:01 PM

Here is what I get:

Code:

[mherring@Ath ~]$ grep -Eo "^[[:alnum:]]+[[:blank:]]" file
odsdsdoddf112
dad23392eeedJ
Hello
garbage

This is what I would expect. The Regex says: "at the beginning of the line, match at least one alphanumeric character, followed by a blank. (blank means ( I think) a non-printing character, but not a line feed.

Once it matches the regex, it won't look at the rest of the line.

Andrew Dufresne · 09-30-2009, 10:04 PM

Quote:

Originally Posted by Kenhelm

I get different output according to which version of It looks as though there is a bug in 'grep -o' version 2.5.1
The 'Beginning-of-line' which is matched by '^' seems to get placed after the last matched sub-string before the next match attempt. So '^' can end up matching positions in the middle of the line.
e.g. (using grep version 2.5.1)

Code:

echo "abcdefghi" | grep -o '^...'
abc
def
ghi               # Output should have been only 'abc'

# It's not that '^' is just being ignored
echo "ab" | grep -o '^b'
            # No output,  '^' has worked.

Thanks a lot Kenhelm. The idea of a bug in GNU grep never crossed my mind.

I have installed grep 2.5.4 and this time it has worked.

Thanks to all of you for helping me.

SharpyWarpy · 09-30-2009, 10:52 PM

To OP: Where did you get grep-2.5.4 ? I need it for my fc10 too. Thanks.

Andrew Dufresne · 09-30-2009, 10:57 PM

Quote:

Originally Posted by SharpyWarpy

To OP: Where did you get grep-2.5.4 ? I need it for my fc10 too. Thanks.

This is the link to GNU ftp mirror site grep section

http://www.promotionalpromos.com/mirrors/gnu/gnu/grep/

And this the file which I downloaded

http://www.promotionalpromos.com/mir...p-2.5.4.tar.gz

Regards

SharpyWarpy · 09-30-2009, 11:29 PM

Thanks bunches to one and all.

pixellany · 10-01-2009, 02:38 PM

wow!!! Here I am with RHEL 5.3----supposedly super-stable, conservative, etc.---but it has GREP v.2.5.1--bugs and all.

And, because it's RHEL, I can't do "pacman -Syu"