Answer by David Foerster for convert txt file to csv seperated with tabs

Ok, so you need to replace the first two and the last space in every line with a comma. You can't just replace every space, because the 3rd field may contain spaces itself. You can do this with regular expression replacement. Here's a sed script/command, that works:

sed -re 's/^(\S*) (\S*) (.*) (\S+)\s*$/\1,\2,\3,\4/' in.txt > out.csv

With the above example this returns:

Account,Units,Description,Delta
2281,19,Toshiba PX-1982GRSUB,0
9618,200,HP MX19942-228b,-25
19246,4,CompuCom HD300g Hard Drive,4

This is still quite fragile with handling empty fields and breaks entirely, if columns other than the 3rd contain spaces. It's very easy to introduce such malformed data if it is formatted manually as done by your boss. You should suggest to him to switch to a more robust table format (e. g. proper CSV & Co.) and editor (common spread sheet tools can manipulate CSV quite well and flexibly, e. g. LibreOffice/OpenOffice Calc, Microsoft Excel and Google Docs).