grep command uses the Xiang solution

grep is a powerful text search tool under Linux

grep: (Global search Regular expression (RE) and print out of the line

Principle: According to the user-specified text pattern, the text is searched line by line, displaying the rows that are matched by the pattern.

grep can use regular expressions for pattern matching

Format:grep [options] ' PATTERN ' file,...

Note: The use of single quotation marks is recommended for characters that do not have special meanings such as variables, or double quotes ""

Common options:
- v: Reverse, showing the line that cannot be matched to by the pattern;
- o: Displays only the strings that are matched by the pattern, not the entire row;
-I: Character case insensitive, ignore-case
- E: extended Regular expression support
-A #: Displays matching lines to the next # line that matches to
- b #: Displays matching lines to the top # lines that are attached to the display
- C #: Show matching lines, append display to the top and bottom # lines

--color=auto : Make matching text appear in color

Example:

1. Display the lines in the/proc/meminfo file that begin with the case s;

# grep-i ' ^s '/proc/meminfo #-I means case insensitive # grep ' ^[ss] '/proc/meminfo # [] brackets denote one of the character sets

2, remove the default shell for non-bash users;

# grep ' bash$ '/etc/passwd # Linux Chinese this defaults to $ as Terminator

3. Remove the user whose default shell is bash and its ID number is the largest;

# grep ' bash$ '/etc/passwd | Sort-n-T:-k3 | Tail-1 | Cut-d:-f1

4, display/etc/rc.d/rc.sysinit file, start with #, followed by at least one white space character, and then have at least one non-whitespace character line;

# grep ' ^#[[:space:]]\{1,\}[^[:space:]\{1,\} '/etc/rc.d/sysinit

5. Display the line beginning with at least one blank character in/boot/grub/grub.conf;

# grep ' ^[[:space:]]\{1,\} '/boot/grub/grub.conf

6, find out the/etc/passwd file in one or two digits;

# grep ' \<[0-9]\{1,2\}\> '/etc/passwd #其中一对尖括是用来锚定的, otherwise like 1234, such a number will also match, the topic of the clear 1-bit or 2-bit

7. Find the integer between 1 and 255 in the result of ifconfig command;

# Ifconfig | Grep-e--color=auto "\< ([1-9]|[ 1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]) \> "

8. View all the information of the root user on the current system;

grep ' ^root\> '/etc/passwd

9, add user bash and Testbash, basher, and then find the current system on its user name and the default shell of the same user;

# Useradd bash; useradd Testbash; Useradd basher # Multiple commands separated by semicolons # grep ' ^\ ([[: alnum:]]\{1,\}\). *\1$ '/etc/passwd

10. Find the line ending with "LISTEN" or "established" in the result of netstat-tan command execution;

# Netstat-tan | Grep-e--color=auto ' (listen| Established) [[: space:]]*$ '

11, remove all the users of the current system shell, requirements: Each shell is displayed only once, and in ascending order;

# cut-d:-f7/etc/passwd | Sort-u

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grep command uses the Xiang solution