mjhjmtu

How can I search a text in a file that matches such condition: starts with 'x' and and have at least 1 'a' immediately after the 'x' and at most 2 'a's immediately following the 'a'.

I tried something like

grep -i ^xa1..2 textfile.txt

but I think I am not understanding the usage of it

$ cat ip.txt 
xe
xa
xaaaalt
xaaa
xaa

$ # match 'a' 1 to 3 times
$ grep -i '^xa1,3' ip.txt
xa
xaaaalt
xaaa
xaa

$ # with ERE, no need to escape 
$ grep -iE '^xa1,3' ip.txt
xa
xaaaalt
xaaa
xaa

To prevent matching more than three consecutive a matching, you'd need

$ grep -iE '^xa1,3([^a]|$)' ip.txt
xa
xaaa
xaa

$ # or lookarounds with PCRE
$ grep -iP '^xa1,3(?!a)' ip.txt
xa
xaaa
xaa

You were close:

grep -i -E '^xaa0,2' textfile.txt

The syntax n,m (with , and not ..) is an extended regexp, hence the -E option. and need to be quoted so that the shell doesn't interpret them.

Given the input

1 x
2 xa
3 xaa
4 xaaa
5 xaaaa

Lines 2, 3 and 4 will be returned by

grep -wE 'xa1,3'

The extended regular expression xa1,3 will match any x followed by between 1 and 3 a. The -w option to grep makes sure that the matching text in the input is a complete word (which is why line 5 is not returned).