Find out on which line in text file is matching word

Yes, its possible with the -n option of grep.

From man grep:

-n, --line-number
              Prefix each line of output with the 1-based line number within its input file.

For example, if you have a file named file.txt having:

this is
foo test
and this is
bar test

Now the output of grep -n "test" file.txt:

$ grep -n "test" file.txt 
2:foo test
4:bar test

Here 2 and 4 indicates the line numbers where the pattern is found.

The grep approach is the simplest but these will all print the line number of the line matching pat:

1. Perl

   perl -lne 'print $. if /pat/' file
   

2. awk

   awk '/pat/{print NR}'
   

3. sed

   sed -n '/pat/=' file