Regular Expressions of Linux

Complaining is just an act of incompetence, without it. --Brother Ma, it's always a positive energy.

• Regular Expressions:

  • Understanding: A pattern that is pieced together by a meta-character and a normal character, summed up by the corresponding "formula" based on certain characteristics of the target character or string

  • Function: can be used for file lookup, pattern matching, etc.

  • Character Matching:

    • .: Matches any single character

    • []: matches any single character within the specified range

    • [^]: matches any single character outside the specified range.

  • Number of matches:

    • *: The characters on the left appear any time

    • . *: Any character of any length
      

    • \?: the character on its left appears 0 times or 1 this

    • \+: The character on the left side appears 1 or more times

    • \{m\}: Exact match to its left character appears m this

    • \{m,n\}: Matches its left character at least m times, up to N times

  • Location anchoring:

    • ^: Anchoring the beginning of the line

    • $: Anchor Line End

    • \<: Anchor Word first

    • \>: Anchor ending

    • ^$: Matches blank lines, including lines with only spaces and tabs!!!

    • \ (\): group. This feeling is relatively tall yet. In the grouping mode, the characters that are matched during a match are memorized temporarily by grep (saved to the built-in variable \1,\2 ... Medium), therefore

    • \1: Refers to the first parenthesis from left to right and the corresponding bracketed contents
      
      

• Practice as follows:

  • Find the lines in the/proc/meminfo file that begin with uppercase s or lowercase s:

    • grep--color=auto "[^ss]"/proc/meminfo

  • Displays users and default shells whose default shell is non-/sbin/nologin in the/etc/passwd file

    • Grep-v "/sbin/nologin$"/etc/passwd | Cut-d:-f1,7

      
      

  • Displays one or two digits in the/etc/passwd file (not including three-bit and measurements-digits)

    • grep "\<[0-9]\{1,2\}\>"/etc/passwd
      

  • Displays lines in the/boot/grub/grub.conf file that begin with at least one white space character followed by the I character

    • grep "^[[:space:]]\+i"/boot/grub/grub.conf
      

  • Find information about users on your system whose user name and default shell are the same

    • grep "^\ ([[: alnum:]]\>\). *\1$"/etc/passwd

  • D

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This article is from the "Ops Dog" blog, make sure to keep this source http://yunweigou.blog.51cto.com/6299641/1627427

Regular Expressions of Linux