grep command

john83reuben · 12-08-2009, 09:02 PM

Hi,

just wanna know something related to grep.

The contents of my file is

Quote:

cat file.txt
john bravo

when i do a

Quote:

grep [a-z]o file.txt
john bravo

Is there a way to get only the string john and not the whole line.

John

GooseYArd · 12-08-2009, 09:10 PM

Quote:

Originally Posted by john83reuben

Hi,

Is there a way to get only the string john and not the whole line.

John

If you just want the part of the line that matches the pattern you provided to grep, just use grep -o

If you always want the nth column, try:

grep whatever file.txt | awk '{ print $1 }'

$1 gets the first column, $2 the second, and so on.

Tinkster · 12-08-2009, 09:20 PM

Not with grep alone, not with your search string, but:

Code:

echo "john bravo"| egrep -ow "[a-z]+o[a-z]+"
john

ghostdog74 · 12-08-2009, 09:48 PM

Quote:

Originally Posted by Tinkster

Not with grep alone, not with your search string, but:

Code:

echo "john bravo"| egrep -ow "[a-z]+o[a-z]+"
john

here's from the man page

Quote:

In addition, three variant programs egrep, fgrep and rgrep are
available. egrep is the same as grep -E. fgrep is the same as
grep -F. rgrep is the same as grep -r. Direct invocation as either
egrep or fgrep is deprecated, but is provided to allow historical
applications that rely on them to run unmodified.

ghostdog74 · 12-08-2009, 09:50 PM

Quote:

Originally Posted by john83reuben

Hi,

just wanna know something related to grep.

The contents of my file is

when i do a

Is there a way to get only the string john and not the whole line.

John

you should define clearly what your search criteria is. why is "bravo" not included ? is it because you want to omit it whenever nothing follows "o" ?

Tinkster · 12-08-2009, 11:07 PM

Quote:

Originally Posted by ghostdog74

here's from the man page

Goes to show that one needs to keep reading man-pages.
I had no idea it was deprecated. Thank you :}

GrapefruiTgirl · 12-08-2009, 11:15 PM

Quote:

Originally Posted by Tinkster

Goes to show that one needs to keep reading man-pages.
I had no idea it was deprecated. Thank you :}

+1 from me too -- thanks (though I look at the grep man page often enough, I guess I don't read it very intently

because I didn't know that)

Sasha

john83reuben · 12-09-2009, 03:46 AM

Thanks for all the replies.
Actually, I was trying to learn to grab only one preffered string from a line of text. Thats y I asked.

My actual intention is,

my file will consist something like this

Quote:

{+12643834} apple orange {+melon}
6434 {+test} [+jsdhfshdf]

So I would like to grab only the string that starts with {+

Im trying to learn regular expression, but gosshh....<complicating>

One more advice from experts, can I perform the task without using much regex, or can it be done just by awk?

Thanks

ghostdog74 · 12-09-2009, 04:07 AM

the regex to get start of string, is ^, so if you use grep or awk

Code:

grep "^{+" file
awk  '/^{+/' file

if you don't want to use too much regex, you can get string index, then compare with "{+"
eg shell

Code:

while read -r line
do
    # get first 2 characters
    [ "${line:0:2}" == "{+" ] && echo "$line"

done <"file"

or gawk

Code:

gawk 'substr($0,1,2) == "{+"' file

another alternative language, which have clean syntax and strong string parsing capabilities (almost never the need to use regex) , is Python

Code:

for line in open("file"):
    if line[0:2] == "{+":  # or line.lstrip().startswith("{+")
        print line

Tinkster · 12-09-2009, 11:21 AM

Quote:

Originally Posted by john83reuben

Thanks for all the replies.
Actually, I was trying to learn to grab only one preffered string from a line of text. Thats y I asked.

My actual intention is,

my file will consist something like this

Code:

{+12643834} apple orange {+melon}
6434 {+test} [+jsdhfshdf]

So I would like to grab only the string that starts with {+

Im trying to learn regular expression, but gosshh....<complicating>

One more advice from experts, can I perform the task without using much regex, or can it be done just by awk?

Thanks

Code:

echo "{+12643834} apple orange {+melon}
6434 {+test} [+jsdhfshdf]"| grep -Eo '\{\+\w+\}'
{+12643834}
{+melon}
{+test}