Grep-CSV
April 9, 2019
Regular readers of this blog know that. in my day job, I frequently process input files from vendors; almost always, they were created in Excel and arrive in CSV format. Sometimes I have to peek inside the files, looking for invalid data, and I have commonly used grep for that task. Sometimes grep gives me unwanted records, because there is a match in some field that is not the field of interested, and I just ignore the extra records. But the other day I had a mess, with lots of unwanted records, so I used awk to parse out the fields and find the records of interest.
I realized as I was performing that task that it would be useful to have a version of grep that understood the CSV file format. So I wrote grep-csv that takes a field number (counting from 1, like awk) and a regular expression and returns the matching rows of a CSV file.
Your task is to write a grep-csv program. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
Quikie one in Ruby.
require 'csv' def grep_csv(csv_str, col, regex_str) regex = Regexp.new(regex_str) csv_str .lines .select { |line| CSV.parse_line(line)[col-1] =~ regex } .join end puts grep_csv(File.read(ARGV[0]), ARGV[1].to_i, ARGV[2])Given the
example.csvfile look like this:When we run the program like so:
The output is: