This command edits a file in place, performing a global text search/replace. The -p switch tells ruby to place your code in the loop while gets; ...; print; end. The -i tells ruby to edit files in place, and -e indicates that a one line program follows.
ruby -p -i -e '$_.gsub!(/248/,"949")' file.txt
One liner to remove DOS line endings from a file
A Unix or Mac text file uses a single line feed character to mark the end of a line (hex 0A). Files created on DOS or Windows use two characters, carriage return and line feed (hex 0D 0A). This command edits a file in place, removing the carriage returns.
ruby -p -i -e '$_.gsub!(/\x0D/,"")' file.txt
One liner to edit files in place and backup each one to *.old
ruby -p -i.old -e '$_.gsub!(/248/,"949")' *.txt