I have a file whose contents are:
$ cat file1
cfd_V03R37
cfd_V03R38
tried
sed 's/[^0-9]//g' file1 > file2
$cat file1
0337
0338
Is there any way by which i can work on same file and write o/p to the same file instead of using file2
Yes,
use Perl:
perl -i~ -ple'tr/[0-9]//dc' file1
GNU sed supports in place editing.
Yes,
or with tee:
tr -dc '[0-9
]' < file1 | tee file1