Delete the first five characters on any line of a text file in Linux with sed

sed 's/^.....//'

means

replace ("s", substitute) beginning-of-line then 5 characters (".") with nothing.

There are more compact or flexible ways to write this using sed or cut.

Use cut:

cut -c6-

This prints each line of the input starting at column 6 (the first column is 1).

sed 's/^.\{,5\}//' file.dat