clojure.core/line-seq

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Type: function Added: Clojure 1.0 Examples: 4 Runnable: 0

([rdr])

Returns the lines of text from rdr as a lazy sequence of strings. rdr must implement java.io.BufferedReader.

Examples

by juergenhoetzel on 2010-07-24 . May have evaluation errors. ▶

;; Count lines of a file (loses head): (with-open [rdr (clojure.java.io/reader "/etc/passwd")] (count (line-seq rdr)))

by TimMc on 2011-04-03 . May have evaluation errors. ▶

(import '(java.io BufferedReader StringReader)) ;; line terminators are stripped (line-seq (BufferedReader. (StringReader. "1\n2\n\n3"))) ("1" "2" "" "3") ;; empty string gives nil (line-seq (BufferedReader. (StringReader. ""))) nil

by kappa on 2015-01-02 . May have evaluation errors. ▶

;; read from standard input (nth (line-seq (java.io.BufferedReader. *in*)) 2) #_=> 0 #_=> 1 #_=> 2 "2"

by jimka2001 on 2024-04-30 . May have evaluation errors. ▶

;; read a list of lines from a file in the resource directory ;; suppose the resource file xyzzy/names.csv has lines of the following form, ;; and we'd like to collect all the male names from year 1966 ;; ;; gender;name;year;occurrences ;; F;mary;1965;12 ;; M;john;1966;56 ;; F;sally;1971;5 ;; (let [s (clojure.java.io/resource "xyzzy/names.csv")] (with-open [r (clojure.java.io/reader s)] (into #{} (for [line (rest (line-seq r)) :let [[gender name year _] (clojure.string/split line #";")] :when (and (= "1966" year) (= "M" gender))] name))))

Note by nxtk

Documentation says that line-seq returns a lazy sequence, however
the actual return value is a Cons cell of the first line to a LazySeq of
the second line. Calling realized? on the Cons cell will fail with an exception.

(cons (.readLine rdr) (lazy-seq (line-seq rdr)))

Example:
(def rdr (BufferedReader. (StringReader. " 1\n 2\n 3")))
(def x (line-seq rdr))
(class x)
=> clojure.lang.Cons

(realized? x)
=> Execution error (ClassCastException) class clojure.lang.Cons cannot be cast to class clojure.lang.IPending

The first line was eagerly realized by the initial call to the line-seq.
(.readLine rdr)
=> " 2"

See also

• clojure.core/read-line (0)

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