Cookbooks
Clojure
Chapter 6. Files and I/O
Reading a text file

Clojure:
Reading a text file

How to: 

;; Read entire file as string
(slurp "example.txt")

;; Output: "Hello, this is your file content!"

;; Read file line-by-line
(with-open [reader (clojure.java.io/reader "example.txt")]
  (doseq [line (line-seq reader)]
    (println line)))

;; Output:
;; Hello,
;; this is your
;; file content!

Deep Dive

Traditionally, reading files in programming languages was a verbose task with many steps to handle errors and resources. In Clojure, you benefit from the slurp function, an elegant one-liner to grab the whole file’s content. For line-by-line reading, line-seq coupled with with-open ensures efficient and safe file handling. It’s also worth mentioning that while slurp is handy, it’s not ideal for large files due to memory constraints. That’s when line-seq shines, as it reads the file lazily, one line at a time.

Alternatives for reading files in Clojure include using the clojure.java.io/file with functions like reader and constructs like with-open to manage the file handle manually. The trade-off here is between ease of use (slurp) and fine-grained control combined with resource safety (with-open and reader).

Implementation-wise, Clojure’s approach is grounded in Java’s IO classes, therefore when you’re dealing with files in Clojure, you’re dealing with Java’s mature, well-tested libraries, wrapped in a functional idiom. Always keep an eye on resources: open files consume handles and memory, so clean file handling is a neat habit.

See Also

Creating a temporary fileReading command line arguments