Synopsis: number-lines [options] [file...]
number-lines reads from files or standard input and writes each line to standard
output preceded by a line number. It is a simplified version of the unix 'nl'
program. It supports one feature 'nl' does not: the ability to treat the first
line of files as a header. This is useful when working with tab-separated-value
files. If header processing used, a header line is written for the first file,
and the header lines are dropped from any subsequent files.
cat myfile.txt | number-lines --header linenum