I had a series of numbers (stored as a column) representing a physical quantity measured with respect to time. The data was stored as a text file. I had to add the time (in seconds) column before the column in the file. The first row had time of 1 second, the second row had a time of 2 seconds etc. In short, I just needed to add the line number to each row.
Ordinarily, one could use python to open the file, read each row and add a incremental number in front of each row. But with Linux all that I had to do was
nl file1.txt > file2.txt
where 'nl' is the new line command. The file 'file1.txt' contained the one column of numbers, the measured values and 'file2.txt' will contain two columns, the seconds column and the datacolumn.
The new line command can also work across pages, can number headers, footers etc. Please check the man page for more details.
Dec 28, 2009
I found a second method to add line number:
To add line number including blank line
cat -n file1.txt > file2.txt. If you wish to add line numbers only for non-blank lines, use
cat -b file1.txt > file2.txt