How can I open a file and search for a word inside it using Ruby?
问题:
回答1:
All presented solution have a time complexity of O(n). For simplicity I use String#include?
to check for the word. This could be done instead with a regular expression in the form string=~ regex
.
Read the complete file and search in it.
File.read(filename).include?(word)
If your file is very large, this is not an optimal solution, as you would read the complete file into memory and start searching afterwards. Your memory complexity is O(n)
Read the file line by line and search in each line
File.open(filename) do |f|
f.any? do |line|
line.include?(word)
end
end
If your file is very large, but you know your lines are upperbounded by a constant value, you now have a memory complexity of O(1).
Read chunks of the file and search in it
File.open(filename) do |f|
tmp= f.read(1024)
next true if tmp.include?(word)
until f.eof?
tmp= tmp[(-1*word.size)..-1] + f.read(1024)
next true if tmp.include?(word)
end
next false
end
In this variant, we are reading equaly sized chunks from the file. So no matter what the conditions of the file are, our memory complexity is O(1)
回答2:
Something like this might help:
def word_exists_in_file
f = File.open("your_file.txt") #opens the file for reading
f.each do line
print line
if line.match /your_word_to_match/
return true
end
end
false
end
回答3:
File.readlines(file).each {|l| l.grep(/#{exp_search}/).each {|r| puts file + ' : ' + r}}
回答4:
Try gem 'search_in_file', it helps you to search word of phrase in specified file or in many files by path