UNIX for Dummies Questions & Answers

I have a file with over 500 MAC addresses. Each address is on a new line. However, the MACs do not have ":"
I need a script that will read the file, line by line and insert colons in the addresses and then print the results to a new file.

current.txt looks like this
111111111111
222222222222
333333333333


Newfile.txt Needs to look like this:
11:11:11:11:11:11
22:22:22:22:22:22
etc..

Code:

sed 's/../&:/g;s/:$//' inputfile > outputfile

you are the greatest!!! thank you sooo much!

would you mind explaining the command? When I looke at the outputfile it was one long string. How can I delimit each mac by a new line? the output file needs to be read by a windows system. I ran your sed command in cygwin.

The reason is because Cygwin behaves like Unix by default, so the output file is created in Unix format (LF terminators instead of CR/LF). Use this to convert it to Windblows format:

Code:

sed 's/../&:/g;s/:$//' current.txt | unix2dos > newfile.txt

s/../&:/g does a global search and replace for any 2 characters, replacing them by the matched string (&) followed by a ":". This results in 11:11:11:11:11:11:, so the s/:$// part is just to strip off the terminating ":". $ is a special character to match the end of the line.