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Linux/LPIC1/12-grep.md

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+# 📘 **Using `grep` in Linux/Unix**
+
+`grep` (Global Regular Expression Print) is a powerful command-line utility used to search for text patterns in files. Below are common variations of the `grep` command with examples and explanations.
+
+---
+
+## 🔍 Basic Search
+
+```bash
+grep "hello" file1
+```
+
+**Description**:
+Searches for lines containing the word `hello` in `file1`. The search is **case-sensitive**.
+
+---
+
+## 🔍 Case-Insensitive Search
+
+```bash
+grep -i "hello" file1
+```
+
+**Description**:
+Performs a **case-insensitive** search for `hello` in `file1`. Matches `hello`, `Hello`, `HELLO`, etc.
+
+---
+
+## 🔢 Show Line Numbers
+
+```bash
+grep -n "hello" file1
+```
+
+**Description**:
+Displays matching lines **with their line numbers**.
+
+---
+
+## 🔢 Case-Insensitive with Line Numbers
+
+```bash
+grep -in "hello" file1
+```
+
+**Description**:
+Combines `-i` and `-n` to show line numbers and ignore case.
+
+---
+
+## 🚫 Invert Match
+
+```bash
+grep -v "hello" file1
+```
+
+**Description**:
+Shows lines that **do NOT** contain the word `hello`.
+
+---
+
+## 🚫 Invert, Ignore Case, and Show Line Numbers
+
+```bash
+grep -ivn "hello" file1
+```
+
+**Description**:
+Combines all the above:
+
+* `-i`: Ignore case
+* `-v`: Invert match
+* `-n`: Show line numbers
+  Shows all lines that **don’t contain** `hello`, regardless of case, and includes line numbers.
+
+---
+
+## ✅ Summary of Flags
+
+| Flag | Description                |
+| ---- | -------------------------- |
+| `-i` | Ignore case                |
+| `-n` | Show line numbers          |
+| `-v` | Invert the match (exclude) |
+