grep command
1. Function
The grep command in Linux is a powerful text search tool that uses regular expressions to search for text and print out the matching lines. The full name of grep is Global Regular Expression Print, which means the global regular expression version, and its use rights are all users.
2. Format
grep [options]
3. Main parameters (if you forget, you can refer to man grep)
[options] Main parameters:
-c: Only output the count of matching lines.
-I: case-insensitive (only applies to single characters).
-h: Do not display file names when querying multiple files.
-l: When querying multiple files, only output file names that contain matching characters.
-n: Display matching lines and line numbers.
-s: Do not display error messages for nonexistent or no matching text.
-v: Display all lines that do not contain matching text.
4. Examples
- 4.1 Find out which lines of the root and imix strings in the passwd file (passwd is a system file that stores user-related information grep –n “root\|imix” /etc/passwd
- 4.2 Following 4.1, query the information of the first 4 lines and the last 3 lines that meet the conditions
grep –n –B 4 –A 3 “imix” /etc/passed
- 4.3 After entering df , cancel the lines related to tmpfs (df is used to check the disk space usage of the file system of the linux server )
df |grep -v tmpfs
5. Regular
| character | Meaning and Examples |
| ^word | Meaning: The query string (word) is at the beginning of the line Example: Query which line starts with # and list the line number grep -n '^#' express.txt |
| word$ | Meaning: The query string (word) is at the end of the line Example: List which line ends with ! and display the line number grep -n '!$' express.txt |
| . | Meaning: matches any single character Example: Query string starts with eve, eae, eee, ee but not (ee) grep -n 'e.e' express.txt |
| \ | Meaning: Escape characters, remove the special meaning of special symbols Example: Querying which row is left with single quotes ' grep -n \' express.txt |
| * | Meaning: match the previous character ≥ 0 times Example: Query the row where the strings of (es) (ess) (esss) , etc. are located grep -n 'ess *' |
| [list] | Meaning: The specified characters are listed in query[] Example: query aay,afy,aly grep -n 'a[afl]y' express.txt |
| [n1-n2] | Meaning: Query out the specified character Example: Querying for lines starting with an uppercase letter grep -n '^[A-Z]' express.txt |
| [^list] | Meaning: The query is not a list set row (Note: when the ^ is in [], the meaning is reverse selection ) Example: Query the string oog,ood but not oot grep -n 'oo[^t]' express.txt |
| \{n,m\} | significance: \{n,m\} Query to find out that a certain character appears n to m times in a row \{n,\} Query to find out that a character appears more than n times in a row \{n\}Query to find out that a character appears n times in a row Example: Query for rows with 2 to 3 o's between g and g grep -n 'go\{2,3\}g' express.txt |