grep Command Learning

Introduction to 1.GREP commands

the grep command is a very powerful text Search tool in the Linux system, full name global Regular expression Print, which represents the globally regular expression version, which is used by all users. According to a pattern ( pattern) to search for text and display the line of text that conforms to the pattern. The pattern: a matching condition that consists of a combination of metacharacters of the text Word wildcards regular the expression .

2. Command format

grep [Options] PATTERN [FILE ...]

Options option:

-I ignore pattern case

--color with color tags

-V Reverse Lookup

-O displays only strings that are matched by the pattern

-C outputs only the count of matching rows

-N Displays matching lines and line numbers

-V Displays all lines that do not contain matching text

Pattern field:

Regular Expressions:

• Match any single character "." grep ' R.. T '/etc/passwd
• Match the previous character any time "*"
• Match any character of any length ". *" grep ' a.*b '/333/testre
• Matches the previous character 1 or 0 times "\?" grep ' A\?b '/333/testre
• Match the preceding character at least N, up to M "\{n,m\}" grep ' A\{1,3\}b '/333/testre

• The position is defined as the beginning of the line "^", grep ' ^r. T '/etc/passwd
• Position defined as Line end "$", grep ' w$ '/etc/initab
• Blank line "^$", grep ' ^$ '/etc/fstab | Wc-l
• Matches a single character "[]" in a specified range
• Matches a single character "[^]" outside the specified range
• [[:d Igit:]] [[: Lower:]] [[: Upper:]] [[: Space:]] [: Alpha:]] [[: Alnum:]]

For example: Match lines that end with a white space character + number? grep ' [[: space:]]*[[:d igit:]]$ '/etc/initab

• Any character behind it appears as the first word "\<"
• Any character in front of the word "\>" appears as the header
• Grouped content "\ (\)" grep "\ (ab\) *"/333/testre
  

Basic Regular Expressions:

• Character match: "." "[]" "[^]"
• Number of matches: "*" "\?" "\{m,n\}" ". *"
• Location matching: "^" "$" "\<" "\>" "\b" "\ (\) \1 \2 \3"

To extend the regular expression:

GREP-E/Egrep

Number of matches "*"? "+" its pre-character at least once grep-e ' ^[[:space:]]+ '/boot/grup/group.conf '

"|" or grep-e ' C|cat '/333/testre

Example: Find all of the 1-255 integers in/etc/networks

Grep-e--color ' \< ([1-9] | [1-9] [0-9] | 1[0-9][[0-9] | 2[0-4][0-9] | 25[0-5] '/etc/networks

grep Command Learning