文本处理CLI Manual

$grep

使用正则表达式或匹配字符串在文本文件与输出流中搜索内容。

命令语法POSIX Standard

grep [OPTIONS] PATTERN [FILE...]

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Grep 是 Linux/Unix 环境下最著名的文本过滤与正则检索工具，逐行扫描输入内容并输出符合条件的行。

Flag / Option	Description
-i	Ignore case distinctions in both patterns and input data.
-n	Prefix each matched output line with its 1-based line number.
-v	Invert the match to print lines that do NOT match the pattern.
-r, -R	Recursively search all files under each directory.
-c	Suppress normal output and print only the count of matching lines.
-E	Interpret pattern as an Extended Regular Expression (ERE).

#1Search for errors in system log files

grep -i -n "error" /var/log/syslog

Searches /var/log/syslog for case-insensitive occurrences of "error" and prints line numbers.

#2Filter process list through a pipe

ps aux | grep nginx

Pipes process snapshot data and isolates lines containing the nginx web server process.

#3Count total failed authentication attempts

grep -c "Failed password" /var/log/auth.log

Outputs the integer count of failed login attempts without listing every individual line.