3 Examples top

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  user=> (use '[clojure.string :only (replace-first)])
  
  ;; Only replace the first match.
  user=> (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.
  user=> (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.
  user=> (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/6/docs/api/java/util/regex/Pattern.html
  ;; Also the book "Mastering Regular Expressions" by Jeffrey Friedl.
  

  user=> (use '[clojure.string :only (replace-first)]) ;; Only replace the first match. user=> (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. user=> (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. user=> (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/6/docs/api/java/util/regex/Pattern.html ;; Also the book "Mastering Regular Expressions" by Jeffrey Friedl.
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  user=> (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.
  user=> (replace-first "/path/to/file/name" #"^.*/" "")
  "name"
  
  ;; Use *? to match as little as possible.
  user=> (replace-first "/path/to/file/name" #"^.*?/" "")
  "path/to/file/name"
  

  user=> (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. user=> (replace-first "/path/to/file/name" #"^.*/" "") "name" ;; Use *? to match as little as possible. user=> (replace-first "/path/to/file/name" #"^.*?/" "") "path/to/file/name"
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  ;; 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".
  user=> (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 \.
  user=> (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.
  user=> (import '(java.util.regex Matcher))
  java.util.regex.Matcher
  
  user=> (defn re-qr [replacement]
           (Matcher/quoteReplacement replacement))
  #'user/re-qr
  
  user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" (re-qr "$2$1"))
  "fabulous $2$1 foo food"
  

  ;; 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". user=> (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 \. user=> (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. user=> (import '(java.util.regex Matcher)) java.util.regex.Matcher user=> (defn re-qr [replacement] (Matcher/quoteReplacement replacement)) #'user/re-qr user=> (str/replace-first "fabulous fodder foo food" #"f(o+)(\S+)" (re-qr "$2$1")) "fabulous $2$1 foo food"