question on egrep - UNIX for Dummies Questions & Answers

rohitv · #1 (**permalink**) 05-19-2006

Hi
I am trying to use this command:
egrep '^a{2,6}$' testexpr4D

to retreive lines with 2,3,4,5, or 6 a's in a file .
The file testexpr4D has entries like:
a
aa
aaa
aaaa
aaaaa
aaaaaa
123456
ABCDEF

I was expecting to see 5 lines in the output but nothing happens.
Can anyone help please?
Thanks
Rohit

tayyabq8 · #2 (**permalink**) 05-19-2006

Code:

egrep '^a\{2,6\}$' testexpr4D

rohitv · #3 (**permalink**) 05-19-2006

Hi Shreenmotor,
That doesn't work either !

Thanks
Rohit

jim mcnamara · #4 (**permalink**) 05-19-2006

This works:

Code:

 egrep '^(a)(a)?' filename

test:

Code:

kcsdev:/home/jmcnama> cat filename
a
aa
aaa
aaaa
aaaaa
aaaaaa
123456
ABCDEF



kcsdev:/home/jmcnama> egrep '^(a)(a)?' filename
a
aa
aaa
aaaa
aaaaa
aaaaaa

Note:

Code:

 egrep '^(a)+$' filename

is closer to correct - correct being 'find a line of any non-zero length that has only the letter a'

rohitv · #5 (**permalink**) 05-22-2006

Jim,
Your solution fetches all the a's in a file . I need to fetch the lines with
2 to 6 a's in a line
Rohit

vino · #6 (**permalink**) 05-22-2006

Quote:

Originally Posted by shereenmotor

Code:

egrep '^a\{2,6\}$' testexpr4D

shereenmotor, that solution is pretty close, but no cigar !

You are mixing the syntax's of sed and [e]grep.

If it were sed, it would be

Code:

sed -n -e "/^a\{2,6\}$/p" filename

If it were grep it would be

Code:

egrep '^a{2,6}$' filename

ranj@chn · #7 (**permalink**) 05-22-2006

Put a single a before the mentioned pattern. You should get your result.
egrep '^a(a)+$' filename

jim mcnamara · #8 (**permalink**) 05-22-2006

For egrep the limit on the number of allowed matches is expressed {lower,upper}

Code:

egrep '^a{1,6}$'

finds a line made only of one to six characters 'a' -s

rohitv · #9 (**permalink**) 05-23-2006

Hi Ranj,
Your solution works for
egrep '^a(a)+$'

But can you tell me how to interpret this please?

How does this know it needs to select 2.. upto 6 a's ?

Thanks
Rohit

jim mcnamara · #10 (**permalink**) 05-23-2006

It doesn't limit the search to a maximum of 6 a's.
Example test with seven a's:

Code:

/home/jmcnama > echo "aaaaaaa" | egrep '^a(a)+$'
aaaaaaa

try it.

rohitv · #11 (**permalink**) 05-25-2006

Hi Jim,
Thanks for your response but my requirement was really limiting the selection between 2 and 6 a's. (or for that matter a user specified number).
Any clues ?

Rohit

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