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Hello,

I would like to remove duplicate lines from a text file. Thus, if my input file looks like this:
I would like to generate output like this: Using Google I found a small regular expression. Consequently, I activated POSIX regular expressions and tried to replace
by
Unfortunately, I received the error "Invalid regular expression". I tried a very similar expression in a different Editor and it worked. What am I doing wrong?

Thank your very much in advance,

Adrian

TextPad's regular expression engine doesn't allow the use of backreferences in the search string. Your options are:

1. Use the other text editor you tried.
2. Try this tool.
3. Use the Sort function in TextPad (Tools > Sort) and select Delete duplicate lines, provided sorting the file at the same time is acceptable.

In fact, TextPad does allow back-references in a search string; it just doesn't allow them to refer back over a newline.

For example,
\<([^ ]+) \1\>
matches repeated words within a line.

Thank you very much for the fast response. Now that I know why my expression failed I was able to solve the problem with a three step approach:

1. Replacing all newlines by a unique string. 2. Replacing duplicate "lines" 3. Replacing the unique strings by newlines again. It is a little bit ugly, but works for me and can maybe help someone else

Kind regards,

Adrian