File Operations

Overview

Read a file all at once (not recommended for large files):

(slurp "./small_file.txt")

Write data to a file all at once:

(spit "./file.txt" "Ocelots are Awesome!")    ; overwrite existing content
(spit "./log.txt" "2016-07-26 New entry." :append true)

Read a file line-by-line:

(use 'clojure.java.io)
(with-open [rdr (reader "./file.txt")]
    (line-seq rdr)    ; returns lazy-seq
)    ; with-open macro calls (.close rdr)

Write a file line-by-line:

(use 'clojure.java.io)
(with-open [wrtr (writer "./log.txt" :append true)]
    (.write wrtr "2016-07-26 New entry.")
)    ; with-open macro calls (.close wrtr)

Write to a file, replacing existing content:

(use 'clojure.java.io)
(with-open [wrtr (writer "./file.txt")]
    (.write wrtr "Everything in file.txt has been replaced with this text.")
)    ; with-open macro calls (.close wrtr)

Notes:

You can specify URLs as well as files
Options to (slurp) and (spit) are passed to clojure.java.io/reader and /writer, respectively.