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#                   SHELL OPERATORS CHEATSHEET             #
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============================================================
TABLE OF CONTENTS
============================================================
1. Overview
2. Basic Operators
   - Arithmetic Operators
   - Relational Operators
   - Logical Operators
   - String Operators
   - File Test Operators
3. Command Chaining Operators
   - Sequential Execution
   - Conditional Execution
4. Redirection Operators
   - Input Redirection
   - Output Redirection
   - Error Redirection
5. Pipes and Filters
6. Process Control Operators
   - Background Processes
   - Job Control
7. Special Operators
8. Comparisons Table
9. Conclusion

============================================================
1. OVERVIEW
============================================================
Shell operators in Linux are symbols and keywords used for 
command execution, chaining, testing, or manipulating inputs 
and outputs in shell scripts or commands.

============================================================
2. BASIC OPERATORS
============================================================
### Arithmetic Operators
- `+` : Addition (e.g., `expr 5 + 2`)
- `-` : Subtraction (e.g., `expr 5 - 2`)
- `*` : Multiplication (e.g., `expr 5 \* 2`)
- `/` : Division (e.g., `expr 10 / 2`)
- `%` : Modulus (e.g., `expr 5 % 2`)

### Relational Operators (used in `[ ]` or `[[ ]]`)
- `-eq` : Equal to (e.g., `[ $a -eq $b ]`)
- `-ne` : Not equal to
- `-gt` : Greater than
- `-lt` : Less than
- `-ge` : Greater than or equal to
- `-le` : Less than or equal to

### Logical Operators
- `&&` : Logical AND (e.g., `[ $a -gt 10 ] && echo "True"`)
- `||` : Logical OR (e.g., `[ $a -gt 10 ] || echo "False"`)
- `!`  : Logical NOT (e.g., `! [ $a -eq $b ]`)

### String Operators
- `=`  : Equal (e.g., `[ "$a" = "$b" ]`)
- `!=` : Not Equal
- `-z` : String is null
- `-n` : String is not null

### File Test Operators
- `-e` : File exists
- `-f` : File is a regular file
- `-d` : Directory exists
- `-r` : File is readable
- `-w` : File is writable
- `-x` : File is executable

============================================================
3. COMMAND CHAINING OPERATORS
============================================================
### Sequential Execution
- `;` : Execute commands sequentially
  - Example: `cmd1 ; cmd2`

### Conditional Execution
- `&&` : Execute next command only if previous succeeds
  - Example: `cmd1 && cmd2`
- `||` : Execute next command only if previous fails
  - Example: `cmd1 || cmd2`

============================================================
4. REDIRECTION OPERATORS
============================================================
### Input Redirection
- `<` : Redirect input from a file
  - Example: `cmd < input.txt`

### Output Redirection
- `>` : Redirect output to a file (overwrite)
  - Example: `cmd > output.txt`
- `>>` : Append output to a file
  - Example: `cmd >> output.txt`

### Error Redirection
- `2>` : Redirect errors to a file
  - Example: `cmd 2> errors.txt`
- `2>>` : Append errors to a file
  - Example: `cmd 2>> errors.txt`

============================================================
5. PIPES AND FILTERS
============================================================
- `|` : Pass output of one command as input to another
  - Example: `cat file.txt | grep "pattern"`

============================================================
6. PROCESS CONTROL OPERATORS
============================================================
### Background Processes
- `&` : Run command in the background
  - Example: `cmd &`

### Job Control
- `jobs` : List active jobs
- `fg` : Bring job to foreground
- `bg` : Resume background job

============================================================
7. SPECIAL OPERATORS
============================================================
- `` `cmd` `` : Command substitution
  - Example: `output=`date``

- `$(( ))` : Arithmetic expansion
  - Example: `result=$((5 + 2))`

============================================================
8. COMPARISONS TABLE
============================================================
| Operator Type        | Symbol/Keyword     | Example                        |
|----------------------|--------------------|--------------------------------|
| Arithmetic           | `+`, `-`, `*`     | `expr 5 + 2`                  |
| Relational           | `-eq`, `-gt`      | `[ $a -gt $b ]`               |
| Logical              | `&&`, `||`        | `[ $a -gt 10 ] && echo "yes"` |
| Redirection          | `<`, `>`          | `cmd > output.txt`            |
| Pipe                 | `|`               | `cmd1 | cmd2`                 |

============================================================
9. CONCLUSION
============================================================
Shell operators in Linux offer powerful tools for command 
execution, input/output management, logical tests, and process 
control. Mastering these operators enhances your scripting 
skills and command-line efficiency. Use this cheatsheet as a 
quick reference to boost your productivity!

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