regular expression

• Regular expressions often have metacharacters
  • Special characters （ Be careful ： Supported tools grep egrep sed awk）
    • \: Escape character , Escape special characters ,
    • ^: Match the beginning of the line ,^xxxx With xxx start
    • $: Match the end of the line , It's about the same as above
    • .: Match break \n\r Think of any single character
    • [list]: matching list A character in the list
    • [^list]: Reverse it , Match any character in the list
    • *: Match the front face expression 0 Times or more
    • \{n\} : Match the previous subexpression n Time , example :go{2}d、'[O-9]{2}' Match two numbers
    • \{n,\}: Match the preceding subexpression no less than n Time , example : go\{2,\}d、' [0-9]\{2,\}' Match two or more digits
    • \{n,m\}﹔ Match the previous subexpression n To m Time , example : go\{2,3\)d、'[0-9]\{2,3\}' Match two to three digits
• Extended regular expression
  • character ：（ Be careful : Support tools egrep、awk）
    • +: Repeat one or more preceding characters
    • ?: matching 0 One or more previous characters
    • |: similar or,egrep -n 'a|b|c' test.txt” Command to query "a" perhaps "b" perhaps "c" character string
    • (): Find group characters , Think of it as a whole
    • ()+: Match multiple duplicate groups
• example ：
  • Find contains i/o The characters of
    • grep -n 'sh[io]rt' test.txt
  • Reverse filter contains w The characters of
    • grep -n '[^w]oo' test.txt
  • Continuously match the specified number of times
    • grep -n 'o\{2\}' test.txt
  • Match the complete number
    • grep -n '[0-9][0-9]*' test.txt