Shell Programming and Scripting

I have a list like this:

todu
todo
tofe
tafo

I want to grep only the lines where the 2nd and the 4th character are the same.
In this case I would get only "todo".

Thanks.

Code:

egrep '.(.).\1' file

If it is truly the first and fourth character what you are seeking, then

Code:

grep -E '^.(.).\1' file

since it does not match the pattern in any other part of the length of the string.

If you are looking for the said pattern in any word, regardless of the length of it.

Code:

grep -E '\<.(.).\1' file

If you want to limit the pattern to words of four characters length.

Code:

grep -E '\<.(.).\1\>' file

I think the command has a bug, here is the fix.

Code:

egrep '^.(.).\1' infile

$ cat infile
xtodu
ytodo
todo
tofe
tafo

$ egrep '^.(.).\1' infile
todo

$  egrep '.(.).\1' infile
ytodo
todo

---------- Post updated at 10:36 AM ---------- Previous update was at 10:32 AM ----------

by awk

Code:

awk  'BEGIN{FS=""}$2==$4' infile