Ruby: Search file text for a pattern and replace it with a given value?

Question

Learning Ruby. I'm looking for a script to search a file (or list of files) for a pattern and, if found, replace that pattern with a given value.

Thoughts?

Answer 1

Here's a quick short way to do it.

file_names = ['foo.txt', 'bar.txt']

file_names.each do |file_name|
  text = File.read(file_name)
  puts text.gsub(/search_regexp/, "replace string")
end

Answer 2

There isn't really a way to edit files in-place. What you usually do when you can get away with it (i.e. if the files are not too big) is, you read the file into memory (File.read), perform your substitutions on the read string (String#gsub) and then write the changed string back to the file (File.open, File#write).

If the files are big enough for that to be unfeasible, what you need to do, is read the file in chunks (if the pattern you want to replace won't span multiple lines then one chunk usually means one line - you can use File.foreach to read a file line by line), and for each chunk perform the substitution on it and append it to a temporary file. When you're done iterating over the source file, you close it and use FileUtils.mv to overwrite it with the temporary file.

Answer 3

Actually, ruby does have an in-place editing feature. Like perl, you can say

ruby -pi.bak -e "gsub(/oldtext/, 'newtext')" *.txt

This will apply the code in double-quotes to all files in the current directory whose names end with .txt. Backup copies of edited files will be created with a .bak extension (foobar.txt.bak I think).

NOTE: this does not appear to work for multiline searches. For those, you have to do it the other less pretty way, with a wrapper script around the regex.