i hope i can explain dis correctly... i'm currently using sed to manipulate a file containing these types of contents: 23:16:14:14:455:66:14 (figure varies for every record in dat file) the prob is some of those figures are the same. according to de above example, is there a way to change the value of 4th field without affecting the 3rd or 7th?? thanx gildan2020

You can use pattern matching to narrow the scope -s'/:[0-9][0-9]$/:new_value/' would match and change the last field.

You can divide up the search expression using \( \) and then refer to the matching sections in the replace expression using \1 = first section, \2 = second etc: sed 's/\([0-9]*:\)\([0-9]*:\)\([0-9]*:\)\([0-9]*\)\(..*$\)/\1\2\3new!\5/' test.lst

alright, it works!! thanx a lot guys gildan2020

This also works in vi, and the regular expression syntax is pretty much the same in Perl and JavaScript.