Operation and Maintenance
Linux Operation and Maintenance
A brief introduction to Linux grep and regular expressions
A brief introduction to Linux grep and regular expressions
grep is a powerful text search tool that uses regular expressions to search text and prints matching lines. This article will share with you knowledge about Linux grep and regular expressions. Friends who are interested should take a look at it
grep introduction
grep is a powerful text search tool that uses regular expressions to search text and prints matching lines. Usually there are three versions of grep: grep, egrep (equivalent to grep -E) and fgrep. egrep is extended grep, and fgrep is fast grep (fixed string to search text, does not support regular expression references but the query is extremely fast). grep is one of the three musketeers of Linux text processing.
How to use grep
How to use:
grep [OPTIONS] PATTERN [FILE...]
grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]
Common options:
--color=auto: Color the matched text and highlight it;
-i: Ignore the case of characters
-o: Only display matched strings
-v: Display lines that cannot be matched by the pattern
-E: Support the use of extended regular expressions
-q: Silent mode, that is, no information is output
-A #: Display the lines matched by the pattern and the following # lines
-B #: Display the pattern matched Matched lines and the # lines before and after
-C #: Display the lines matched by the pattern and the # lines before and after
Note: When using grep matching, you need to use double quotes (single quotes) Quotation marks are strong quotes) to prevent the system from mistaking it for parameters or special commands and reporting an error.
Extended grep usage
Usage:
##
egrep [OPTIONS] PATTERN [FILE...] grep -E [OPTIONS] PATTERN [FILE...]
-o: Only display the matched string itself
-v: Display lines that are not matched by the pattern
-q: Silent mode, that is, no information is output
-A #: Display the line matched by the pattern and # lines after it
-B #: Display the line matched by the pattern and the # lines before it
-C #: Display the line matched by the pattern and the lines before and after it #Row
-G: Support basic regular expressions
grep regular expression metacharacter
'^': Anchor line Heading '$': Anchor line end '.': Match any one character '*': Match zero or more previous characters '\?': Matches the character before it 0 or 1 times; '\+': Matches the character before it 1 or more times; \{m\}': Match the character before it m times (\ is an escape character) '\{m,n\}': Match the character before it at least m times and at most n times '[]': matches a character within the specified range | '[^]' matches any single character outside the specified range '\<' or '\b': anchor Beginning of the word, '\>' or '\b': anchor the end of the word (available\[:alpha:] matches any single letter
[:alnum:] matches any single letter or number
[:punct:] matches any single symbol
[:space:] Matches a single space
Some places cancel the use of escape characters:
'?': Matches the preceding character 0 or 1 times;
'+': Match the character before it 1 or more times;
'{m}': Match the character before it m times (\ is an escape character)
'{ m,n}': Match the preceding character at least m times and at most n times
(): Bundle one or more characters together and process them as a whole. Backreferences are used as usual.
'|': or (Note: 'C|cat' is C and cat, '(C|c)at is Cat and cat')
Exercise:
1. List the user names of all logged-in users on the current system. Note: If the same user logs in multiple times, it will only be displayed once
[root@localhost ~]# who | cut -d' ' -f1|uniq root
2、取出最后登录到当前系统的用户的相关信息
[root@localhost ~]# id `last | head -1 | cut -d' ' -f1` uid=0(root) gid=0(root) groups=0(root)
3.取出当前系统上被用户当做其默认shell最多的那个shell
[root@localhost ~]# cut -d':' -f7 /etc/passwd|uniq -c|sort -n|tail -1|cut -d' ' -f7 /sbin/nologin
4.将/etc/passd中的第三个字段设置最大的后10个用户的信息全部改为大写保存至/tmp/maxuser.txt文件中
[root@localhost ~]# sort -t':' -k3 -n /etc/passwd|tail -10|tr 'a-z' 'A-Z' >/tmp/maxusers.txt [root@localhost ~]# cat /tmp/maxusers.txt NOBODY:X:99:99:NOBODY:/:/SBIN/NOLOGIN SYSTEMD-NETWORK:X:192:192:SYSTEMD NETWORK MANAGEMENT:/:/SBIN/NOLOGIN NGINX:X:996:994:NGINX WEB SERVER:/VAR/LIB/NGINX:/SBIN/NOLOGIN CHRONY:X:997:995::/VAR/LIB/CHRONY:/SBIN/NOLOGIN POLKITD:X:998:996:USER FOR POLKITD:/:/SBIN/NOLOGIN SYSTEMD-BUS-PROXY:X:999:997:SYSTEMD BUS PROXY:/:/SBIN/NOLOGIN DINGJIE:X:1000:1000:DINGJIE:/HOME/DINGJIE:/BIN/BASH JEFF:X:1001:1024:WOSHIDASHUAIBI:/HOME/JEFF:/BIN/BASH EGON:X:1002:1002::/HOME/EGON:/BIN/BASH NFSNOBODY:X:65534:65534:ANONYMOUS NFS USER:/VAR/LIB/NFS:/SBIN/NOLOGIN
5.取出当前主机的IP地址
[root@localhost ~]# ifconfig | egrep "inet.*broadcast.*"|cut -d' ' -f10 192.168.0.133
6.列出/etc目录下所有已.conf结尾的文件的文件名，并将其名字转换为大写后保存至/tmp/etc.conf文件中
[root@localhost ~]# find /etc -name '*.conf' | egrep -o "[^/]*(\.conf)$"|tr 'a-z' 'A-Z' >/tmp/etc.conf [root@localhost ~]# cat /tmp/etc.conf RESOLV.CONF CA-LEGACY.CONF FASTESTMIRROR.CONF LANGPACKS.CONF SYSTEMD.CONF VERSION-GROUPS.CONF LVM.CONF LVMLOCAL.CONF ASOUND.CONF LDAP.CONF MLX4.CONF RDMA.CONF SMTPD.CONF
7.显示/var目录下一级子目录或文件的总数
[root@localhost ~]# ls /var | wc -l
8.取出/etc/group第三个字段数值最小的10个组的名字
[root@localhost ~]# sort -t: -k3 -n /etc/group|head -10 |cut -d':' -f1 root bin daemon sys adm tty disk lp mem kmem
9.将/etc/fstab和/etc/issue文件的内容合并为同一个内容后保存至/tmp/etc.test文件中
[root@localhost ~]# cat /etc/fstab /etc/issue > /tmp/etc.test [root@localhost ~]# cat /tmp/etc.test # # /etc/fstab # Created by anaconda on Sat May 13 10:12:58 2017 # # Accessible filesystems, by reference, are maintained under '/dev/disk' # See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info # /dev/mapper/cl-root / xfs defaults 0 0 UUID=2789d01a-4e2b-47a5-9c3c-537641648663 /boot xfs defaults 0 0 /dev/mapper/cl-swap swap swap defaults 0 0 \S Kernel \r on an \m
The above is the detailed content of A brief introduction to Linux grep and regular expressions. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
What computer configuration is required for vscode
Apr 15, 2025 pm 09:48 PM
VS Code system requirements: Operating system: Windows 10 and above, macOS 10.12 and above, Linux distribution processor: minimum 1.6 GHz, recommended 2.0 GHz and above memory: minimum 512 MB, recommended 4 GB and above storage space: minimum 250 MB, recommended 1 GB and above other requirements: stable network connection, Xorg/Wayland (Linux)
Linux Architecture: Unveiling the 5 Basic Components
Apr 20, 2025 am 12:04 AM
The five basic components of the Linux system are: 1. Kernel, 2. System library, 3. System utilities, 4. Graphical user interface, 5. Applications. The kernel manages hardware resources, the system library provides precompiled functions, system utilities are used for system management, the GUI provides visual interaction, and applications use these components to implement functions.
How to run java code in notepad
Apr 16, 2025 pm 07:39 PM
Although Notepad cannot run Java code directly, it can be achieved by using other tools: using the command line compiler (javac) to generate a bytecode file (filename.class). Use the Java interpreter (java) to interpret bytecode, execute the code, and output the result.
vscode cannot install extension
Apr 15, 2025 pm 07:18 PM
The reasons for the installation of VS Code extensions may be: network instability, insufficient permissions, system compatibility issues, VS Code version is too old, antivirus software or firewall interference. By checking network connections, permissions, log files, updating VS Code, disabling security software, and restarting VS Code or computers, you can gradually troubleshoot and resolve issues.
vscode terminal usage tutorial
Apr 15, 2025 pm 10:09 PM
vscode built-in terminal is a development tool that allows running commands and scripts within the editor to simplify the development process. How to use vscode terminal: Open the terminal with the shortcut key (Ctrl/Cmd). Enter a command or run the script. Use hotkeys (such as Ctrl L to clear the terminal). Change the working directory (such as the cd command). Advanced features include debug mode, automatic code snippet completion, and interactive command history.
How to check the warehouse address of git
Apr 17, 2025 pm 01:54 PM
To view the Git repository address, perform the following steps: 1. Open the command line and navigate to the repository directory; 2. Run the "git remote -v" command; 3. View the repository name in the output and its corresponding address.
Where to write code in vscode
Apr 15, 2025 pm 09:54 PM
Writing code in Visual Studio Code (VSCode) is simple and easy to use. Just install VSCode, create a project, select a language, create a file, write code, save and run it. The advantages of VSCode include cross-platform, free and open source, powerful features, rich extensions, and lightweight and fast.
Can vscode be used for mac
Apr 15, 2025 pm 07:36 PM
VS Code is available on Mac. It has powerful extensions, Git integration, terminal and debugger, and also offers a wealth of setup options. However, for particularly large projects or highly professional development, VS Code may have performance or functional limitations.
