Remove stuff, retrieve numbers, retrieve text with spaces in place of dots, remove the rest...

Question

Hi All!!
This is my first question, so I hope I didn't mess too much with the title and the formatting.

I have a bunch of file a client of mine sent me in this form:

Name.Of.Chapter.021x212.The.Actual.Title.Of.the.Chapter.DOC.NAME-Some.stuff.Here.ext

What I need is a regex to output just:

212 The Actual Title Of the Chapter

I'm not gonna use it with any script language in particular; it's a batch renaming of files through an app supporting regex (which already "preserves" the extension).

So far, all I was able to do was this:

/.*x(\d+)\.(.*?)\.[A-Z]{3}.*/ -->REPLACE: $1 $2

(Capture everything before a number preceded by an "x", group numbers after the "x", group everything following until a 3 digit Uppercase word is met, then capture everything that follows)
which gives me back:

212 The.Actual.Title.Of.the.Chapter

Having seen the result I thought that something like:

/.*x(\d+)\.([^.]*?)\.[A-Z]{3}.*/ -->REPLACE: $1 $2

(Changed second group to "Capture everything which is not a dot...") would have worked as expected. Instead, the whole regex fails to match completely.

What am I missing?

TIA

cià
ale

Answer 1

.*x(\d+)\. matches Name.Of.Chapter.021x212.

\.[A-Z]{3}.* matches .DOC.NAME-Some.stuff.Here.ext

But ([^.]*?) does not match The.Actual.Title.Of.the.Chapter because this regex does not allow for any periods at all.

Answer 2

since you are on Mac, you could use the shell

$ s="Name.Of.Chapter.021x212.The.Actual.Title.Of.the.Chapter.DOC.NAME-Some.stuff.Here.ext"

$ echo ${s#*x}
212.The.Actual.Title.Of.the.Chapter.DOC.NAME-Some.stuff.Here.ext

$ t=${s#*x}

$ echo ${t%.[A-Z][A-Z][A-Z].*}
212.The.Actual.Title.Of.the.Chapter

Or if you prefer sed, eg

echo $filename | sed 's|.[^x]*x||;s/\.[A-Z][A-Z][A-Z].*//' 

For processing multiple files

for file in *.ext
do
  newfile=${file#*x}
  newfile=${newfile%.[A-Z][A-Z][A-Z].*}
  # or 
  # newfile=$(echo $file | sed 's|.[^x]*x||;s/\.[A-Z][A-Z][A-Z].*//')
  mv "$file" "$newfile"
done 

Answer 3

To your question "How can I remove the dots in the process of matching?" the answer is "You can't." The only way to do that is by processing the result of the match in a second step, as others have said. But I think there's a more basic question that needs to be addressed, which is "What does it mean for a regex to match a given input?"

A regex is usually said to match a string when it describes any substring of that string. If you want to be sure the regex describes the whole string, you need to add the start (^) and end ($) anchors:

/^.*x(\d+)\.(.*?)\.[A-Z]{3}.*$/  

But in your case, you don't need to describe the whole string; if you get rid of the .* at either end, it will serve your just as well:

/x(\d+)\.(.*?)\.[A-Z]{3}/  

I recommend you not get in the habit of "padding" regexes with .* at beginning and end. The leading .* in particular can change the behavior of the regex in unexpected ways. For example, it there were two places in the input string where x(\d+)\. could match, your "real" match would have started at the second one. Also, if it's not anchored with ^ or \A, a leading .* can make the whole regex much less efficient.

I said "usually" above because some tools do automatically "anchor" the match at the beginning (Python's match()) or at both ends (Java's matches()), but that's pretty rare. Most of the shells and command-line tools available on *nix systems define a regex match in the traditional way, but it's a good idea to say what tool(s) you're using, just in case.

Finally, a word or two about vocabulary. The parentheses in (\d+) cause the matched characters to be captured, not grouped. Many regex flavors also support non-capturing parentheses in the form (?:\d+), which are used for grouping only. Any text that is included in the overall match, whether it's captured or not, is said to have been consumed (not captured). The way you used the words "capture" and "group" in your question is guaranteed to cause maximum confusion in anyone who assumes you know what you're talking about. :D

If you haven't read it yet, check out this excellent tutorial.