Remove odd lines from a text file
I'd like to find a way to remove odd lines from a text file. I've found examples of removing lines, but in those cases they were the first or last three lines, or else lines that contained a certain word, and I haven't been able to adapt them to my needs (not to surprise, being a newbie).
I suppose it could probably be done with sed, but my knowledge about it is zero.
I'm open to any suggestion: a pipe, a bash/perl script, sed/awk...
I know this will probably be a lame question for most of you, so I appeal to your indulgence.
Many thanks in advance.