Reading from a File

Suppose we have a file in the same directory as our nim program, kittens.txt with the following contents.


We can use the readFile proc to read the entire file into memory.

# This will read the entire file into the string entireFile
let entireFile = readFile("kittens.txt")
echo entireFile  # prints the entire file

We can also read the lines of a file by opening a File object and using the readLine proc to read individual lines.

proc readKittens() =
  let f = open("kittens.txt")
  # Close the file object when you are done with it
  defer: f.close()

  let firstLine = f.readLine()
  echo firstLine  # prints Spitfire


Writing to a File

We can write a string to a file using the writeFile proc.

let text = "Cats are very cool!"
writeFile("cats.txt", text)

This will create a file on the system named cats.txt containing “Cats are very cool!”

We can also write a file line by line using a File object and the writeLine proc.

proc writeCatActivities() =
  let lines = ["Play", "Eat", "Sleep"]
  # The fmWrite constant specifies that we are opening the file for writing.
  let f = open("catactivities.txt", fmWrite)
  defer: f.close()

  for line in lines:


After running this program there should be a file called catactivities.txt with the following contents.