正则表达式中的特殊字符
发布时间：2020-12-13 19:55:04 所属栏目：百科 来源：网络整理
导读：The special characters recognized by regular expressions are: .*[]^${}+?|() Anchor characters caret character (^) Starting at the beginning dollar sign ($) Looking for the ending dot character (.) Match any single character except a newlin
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The special characters recognized by regular expressions are:
.*[]^${}+?|() Anchor characters caret character (^) Starting at the beginning dollar sign ($) Looking for the ending dot character (.) Match any single character except a newline character. Character classes [abc] [0123456789] Looking for a character contained in the class Negating character classes [^ch]at Looking for any character that’s not in the class Using ranges [a-c] [0-9] noncontinuous ranges [a-ch-k] Special character classes [[:digit:]] [[:alpha:]] The asterisk (*) Placing an asterisk after a character signifies that the character must appear zero or more times in the text to match the pattern [test]$ echo "I ate a potatoe with my lunch." | sed -n /potatoe*/p I ate a potatoe with my lunch. [test]$ echo "I ate a potato with my lunch." | sed -n '/potatoe*/p' I ate a potato with my lunch. combining the dot special character with the asterisk special character to match any number of any characters. [test]$ echo "this is a regular pattern expression" | sed -n '/regular.*expression/p' this is a regular pattern expression The question mark (?) indicates that the preceding character can appear zero or one time [test]$ echo "bt" | gawk '/be?t/{print $0}' bt [test]$ echo "bet" | gawk '/be?t/{print $0}' bet [test]$ echo "beet" | gawk '/be?t/{print $0}' # no match The plus sign indicates that the preceding character can appear one or more times,but must be present at least once. [test]$ echo "beet" | gawk '/be+t/{print $0}' beet [test]$ echo "bet" | gawk '/be+t/{print $0}' bet [test]$ echo "bt" | gawk '/be+t/{print $0}' # no match Curly braces to allow you to specify a limit on a repeatable regular expres-sion. This is often referred to as an interval [test]$ echo "bt" | gawk --re-interval '/be{1}t/{print $0}' # no match [test]$ echo "bet" | gawk --re-interval '/be{1}t/{print $0}' bet [test]$ echo "beet" | gawk --re-interval '/be{1}t/{print $0}' # no match [test]$ echo "beet" | gawk --re-interval '/be{1,2}t/{print $0}' beet [test]$ echo "beeet" | gawk --re-interval '/be{1,2}t/{print $0}' # no match [test]$ echo "bet" | gawk --re-interval '/be{1,2}t/{print $0}' bet [jialiang@ht191w script]$ echo "bt" | gawk --re-interval '/be{1,2}t/{print $0}' # no match The pipe symbol (|) allows to you to specify two or more patterns that the regular expression engine uses in a logicalORformula when examining the data stream. [test]$ echo "The cat is asleep" | gawk '/cat|dog/{print $0}' The cat is asleep [test]$ echo "The dog is asleep" | gawk '/cat|dog/{print $0}' The dog is asleep [test]$ echo "The dogcat is asleep" | gawk '/cat|dog/{print $0}' The dogcat is asleep [test]$ echo "The dog cat is asleep" | gawk '/cat|dog/{print $0}' The dog cat is asleep [test]$ echo "The cdogat is asleep" | gawk '/cat|dog/{print $0}' The cdogat is asleep Grouping expressions,When you group a reg-ular expression pattern,the group is treatedlike a standard character. [test]$ echo "Sat" | gawk '/Sat(urday)?/{print $0}' Sat [test]$ echo "Satur" | gawk '/Sat(urday)?/{print $0}' Satur [test]$ echo "Saturdd" | gawk '/Sat(urday)?/{print $0}' Saturdd [test]$ echo "Saturday" | gawk '/Sat(urday)?/{print $0}' Saturday （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |