- generate_data | sed -e 's/x/y/'
That is, generate the data, but make these small changes.
Sed is one of the very early unix commands that permitted command line processing of data files. Cousin to the later AWK, sed allowed powerful and interesting data processing to be done by shell scripts. Sed was probably the earliest Unix tool that really encouraged regular expressions to be used ubiquitously.
Sed and AWK are often cited as the progenitors and inspiration for Perl.