for doc bash script

Linux/Bash Script/9-For.md

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+# Bash `for` Loop Cheat Sheet
+
+A clear and concise reference for using `for` loops in Bash, with syntax variations, examples, and best practices.
+
+---
+
+## 1. Basic `for` Loop (List Iteration)
+
+Iterates over a fixed list of items.
+
+**Syntax:**
+
+```bash
+for VARIABLE in ITEM1 ITEM2 ITEM3 ...
+do
+  commands
+DONE
+done
+```
+
+**Example:**
+
+```bash
+for color in red green blue
+do
+  echo "Color: $color"
+done
+```
+
+*Output:*
+
+```
+Color: red
+Color: green
+Color: blue
+```
+
+---
+
+## 2. Numeric Iteration Using a List
+
+When you explicitly list out numbers.
+
+**Example:**
+
+```bash
+for i in 1 2 3 4 5
+do
+  echo "Number: $i"
+done
+```
+
+*Output:*
+
+```
+Number: 1
+Number: 2
+Number: 3
+Number: 4
+Number: 5
+```
+
+---
+
+## 3. C-style `for` Loop (Arithmetic)
+
+Similar to loops in C-style languages: initialize, condition, increment.
+
+**Syntax:**
+
+```bash
+for (( init; condition; increment ))
+do
+  commands
+ndone
+```
+
+**Example:**
+
+```bash
+for (( i=0; i<5; i++ ))
+do
+  echo "Index: $i"
+done
+```
+
+*Output:*
+
+```
+Index: 0
+Index: 1
+Index: 2
+Index: 3
+Index: 4
+```
+
+---
+
+## 4. Looping Over Files (Globbing)
+
+Use shell glob patterns to iterate over matching filenames.
+
+**Example:**
+
+```bash
+for file in *.txt
+do
+  echo "Found text file: $file"
+done
+```
+
+```
+# If the directory contains a.txt and notes.txt, output might be:
+Found text file: a.txt
+Found text file: notes.txt
+```
+
+---
+
+## Summary
+
+| Style             | Purpose                                    | Notes                                 |
+| ----------------- | ------------------------------------------ | ------------------------------------- |
+| `for var in list` | Iterate over a static list or glob results | Most common in shell scripting        |
+| `for (( ... ))`   | Numeric / arithmetic loops                 | C-style syntax, powerful for counters |
+