Try the following approach

• open file 1 for reading and file 2 for writing
• for each line in file 1 do
• parse it by columns (e.g.  $lineIn =~ /(SWITCH)( FastEthernet)(\d)(.*)/;)
• create the output format (re-ordering the columns) (e.g.  $lineOut = "$1$3$2$4";)
• write the output to file 2

Probably you need some fine-tuning with the regular expressions ;-)

HTH, Rata