Linux Regular Expressions

Linux Regular Expressions
Grep: linux Text Processing Sankey: grep: text filtering tool sed: Text editor (line); stream editor awk: Text report editor; Linux awk implementation gawk; grep: global search REgularexpression and Print out the line. purpose: Use a text search tool to search for the target text line by line based on the user's pattern and print the matched rows. Mode: filter condition metacharacters written by metacharacters of regular expressions and text characters: A character does not represent its literal meaning, but is used to indicate wildcard or control functions. There are two types: Basic Regular Expressions: BRE extension Regular Expression Engine: ERE Regular Expression Engine: grep [OPTIONS] PATTERN [FILE...]: Option: -- color = auto: highlight the matched string;-v: The display mode does not match the row;-I: Ignore the case sensitivity;-o: only display the strings that can be matched by the pattern;-q: silent mode;-E: use an extended regular expression; metacharacter of the basic regular expression: character match :.: match any single character; []: match any single character in the specified range; [^]: match any single character in the specified range; [: lower:], [: upper:],... number of times matching: used to specify the characters behind the number of times; *: Any time; abxy xay xxxxxxxy grep "x * y "\?: 0 or 1 time; grep "x \? Y "\ +: 1 or multiple times; \ {m \}: The exact limit is MB; \ {m, n \}: At least m times, up to n times, [m, n] \ {0, n \}: up to n times; \ {m, \}: At least m times ;. *: match any character of any length; position anchoring: ^: First row anchoring; leftmost of the pattern; $: Last Row anchoring; rightmost pattern; \ <, \ B: the beginning of a word; used to represent the left side of the word's pattern; \>, \ B: the end of a word; used to represent the right side of the pattern of a word; ^ $: blank rows; the pattern matching content in the parentheses of the group \ (\) will be recorded by the Regular Expression Engine During execution and saved in the built-in variables; these variables are \ 1, \ 2 ,... \ 1: Starting from the left, the first left bracket, and the matching content of the pattern in the middle of the matching right brace; \ 2 :... backward reference: Use a variable to reference the characters matching the pattern in the group brackets. The extended regular expression: grep family has three commands: grep: Basic regular expression-E: extended Regular Expression -F: the regular expression egrep is not supported. The extended regular expression fgrep is not supported. 1. The line ending with bash in the/etc/passwd file is displayed. [root @ localhost ~] # Grep -- color = auto'bash $ '/etc/passwd root: x: 0: 0: root:/bin/bash wengangwang: x: 1000: 1000: wengangwang:/home/wengangwang:/bin/bash 2. display two or three digits in the/etc/passwd file. [root @ localhost ~] # Grep -- color = auto "[[: digit:] \ {2, 3 \}"/etc/passwd mail: x: 8: 12: mail: /var/spool/mail:/sbin/nologin operator: x: 11: 0: operator:/root:/sbin/nologin games: x: 12: 100: games: /usr/games:/sbin/nologin ftp: x: 14: 50: FTP User:/var/ftp:/sbin/nologin nobody: x: 99: 99: Nobody: //:/sbin/nologin logs: x: 81: 81: System message bus: //:/sbin/nologin polkitd: x: 999: 999: User for polkitd :/: /sbin/nologin 3. display the 'netstat-tan' command result with 'LIST' EN 'followed by a line ending with 0, 1, or multiple blank characters [root @ localhost ~] # Netstat-tan | egrep 'Listen [[: space:] * $ 'tcp 0 0 0.0.0.0: 22 0.0.0.0: * LISTEN tcp 0 0 127.0.0.1: 631 0.0.0.0: * LISTEN tcp 0 127.0.0.1: 25 0.0.0.0: * LISTEN tcp6 0 0: 22: * LISTEN tcp6 0 0 0: 1: 631 ::: * LISTEN tcp6 0 0: 1: 25: * LISTEN 4. Add bash, testbash, basher, and nologin users (the shell of nologin users is/sbin/nologin ); then find the line with the same username as the shell name in the/etc/passwd file [root @ localhost ~] # Useraddbash; useradd testbash; useradd busher; useradd-s/sbin/nologin [root @ localhost ~] # Grep "\ (bash \). * \ 1 "/etc/passwdbash: x: 3002: 3002:/home/bash:/bin/bashtestbash: x: 3003: 3003:/home/testbash: /bin/bash 5. display the default shell and UID of the root, centos, or user1 users on the current system (Please create these users in advance if they do not exist) [root @ localhost ~] # Egrep '^ root | ^ centos | ^ user1'/etc/passwd | cut-d:-f3, 70:/bin/bash3006:/bin/bash3007: /bin/bash [root @ localhost ~] # Egrep -- color = auto' (^ \ <root \> | ^ \ <centos \> | ^ \ <user1 \>) '/etc/passwdroot: x: 0: 0: root:/bin/bashcentos: x: 3006: 3006:/home/centos:/bin/bashuser1: x: 3007: 3007 :: /home/user1:/bin/bash 6. Find/etc/rc. d/init. A word in the d/functions file (which can contain underscores in the middle of the word) followed by a group of parentheses [root @ localhost ~] # Grep '. * () '/etc/rc. d/init. d/forward () {checkpid () {__ readlink () {__ fgrep () {__ umount_loop () {__ umount_loopback_loop () {__ pids_var_run () {__ pids_pidof () {daemon () {killproc () {pidfileofproc () {pidofproc () {status () {Summary () {echo_passed () {echo_warning () {update_boot_stage () {success () {failure () {passed () {warning () {action () {action_silent () {strstr () {co Nfirm () {get_numeric_dev () {is_ignored_file () {is_true () {is_false () {apply_sysctl () {key_is_random () {encrypt () {init_crypto () {7. Use echo to output a path, and then find the base name of the path. Use egrep to retrieve the directory name [root @ localhost ~]. # Echo/etc/passwd | egrep -- color = auto-o "[[: alnum:] + \/? $ "Passwd [root @ localhost ~] # Echo/etc/passwd/| egrep -- color = auto-o "^ \/. * \/"/etc/passwd/8. Find the number between 1-In the ifconfig command execution result [root @ localhost ~] # Ifconfig | egrep '\ <([1-9] | [1-9] [0-9] | 1 [0-9] [0-9] | 2 [0 -4] [0-9] 25 [0-5]) \> 'inet 192.168.88.106 netmask00000000255.0 broadcast 192.168.88.255 inet6 fe80: 20c: 29ff: fe7b: rjc prefixlen 64 scopeid 0x20 <link> ether 00: 0c: 29: 7b: 34: 7c txqueuelen 1000 (Ethernet) RX packets 144034 bytes202904157 (193.5 MiB) TX packets 64975 bytes 4455917 (4.2 MiB) lo: flags = 73 <UP, LOOPBACK, RUNNING> mtu 65536 inet 127.0.0.1 netmask1_0.0.0 inet6: 1 prefixlen 128 scopeid 0x10