clojure.string/replace-first

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Type: function Added: Clojure 1.2 Examples: 4 Runnable: 3

([s match replacement])

Replaces the first instance of match with replacement in s.

match/replacement can be:

char / char string / string pattern / (string or function of match).

See also replace.

The replacement is literal (i.e. none of its characters are treated specially) for all cases above except pattern / string.

For pattern / string, $1, $2, etc. in the replacement string are substituted with the string that matched the corresponding parenthesized group in the pattern. If you wish your replacement string r to be used literally, use (re-quote-replacement r) as the replacement argument. See also documentation for java.util.regex.Matcher's appendReplacement method.

Example: (clojure.string/replace-first "swap first two words" #"(\w+)(\s+)(\w+)" "$3$2$1") -> "first swap two words"

Examples

by jafingerhut on 2011-12-15 ▶

(use '[clojure.string :only (replace-first)]) ;; Only replace the first match. (replace-first "A good day to you, sir. Good day." #"day" "night") "A good night to you, sir. Good day." ;; If there are no matches, return the original string. (replace-first "A good day to you, sir." #"madam" "master") "A good day to you, sir." ;; (?i) at the beginning of a pattern makes the entire thing match ;; case-insensitively, at least for US ASCII characters. (?u) does ;; the corresponding thing for Unicode. (replace-first "Day need not be SHOUTED." #"(?i)day" "night") "night need not be SHOUTED." ;; See here for many details on regex patterns: ;; http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html ;; Also the book "Mastering Regular Expressions" by Jeffrey Friedl.

by jafingerhut on 2011-12-15 ▶

(use '[clojure.string :only (replace-first)]) ;; Pattern matches from beginning of string (signified by ^) up to the ;; last occurrence of /, because by default * is greedy, i.e. it ;; matches as much as possible. (replace-first "/path/to/file/name" #"^.*/" "") "name" ;; Use *? to match as little as possible. (replace-first "/path/to/file/name" #"^.*?/" "") "path/to/file/name"

by jafingerhut on 2011-12-21 . May have evaluation errors. ▶

;; Note: When replace-first or replace have a regex pattern as their ;; match argument, dollar sign ($) and backslash (\) characters in ;; the replacement string are treated specially. ;; Example: pattern matches string "fodder", with (o+) matching "o" ;; and (\S+) matching "dder". Replacement string says to replace the ;; entire match "fodder" with $2, the string matched by the second ;; parenthesized group, "dder", followed by $1, "o". (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" "$2$1") "fabulous ddero foo food" ;; To avoid this special treatment of $ and \, you must escape them with ;; \. Because it is in a Clojure string, to get one \ we must escape ;; *that* with its own \. (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" "\\$2\\$1") "fabulous $2$1 foo food" ;; To ensure the replacement is treated literally, call ;; java.util.regex.Matcher/quoteReplacement on it. A shorter name ;; like re-qr can be handy. (import '(java.util.regex Matcher)) java.util.regex.Matcher (defn re-qr [replacement] (Matcher/quoteReplacement replacement)) #'user/re-qr (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" (re-qr "$2$1")) "fabulous $2$1 foo food"

by jafingerhut on 2013-09-13 ▶

;; Note: See clojure.core/subs for discussion of behavior of substrings ;; holding onto references of the original strings, which can ;; significantly affect your memory usage in some cases.

See also

• clojure.string/replace (8)
• clojure.core/re-pattern
• clojure.core/subs (3)
• clojure.string/re-quote-replacement

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