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technology/applications/cli/Shell.md
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@ -2,8 +2,9 @@
obj: concept obj: concept
arch-wiki: https://wiki.archlinux.org/title/Command-line_shell arch-wiki: https://wiki.archlinux.org/title/Command-line_shell
wiki: https://en.wikipedia.org/wiki/Unix_shell wiki: https://en.wikipedia.org/wiki/Unix_shell
rev: 2024-03-07 rev: 2024-09-05
--- ---
# Shell # Shell
The shell is a command-line interpreter that provides a user interface to an operating system's services. It allows users to interact with the system through text-based commands and scripts. Shell scripting refers to writing a series of commands in a script file to automate tasks and perform complex operations. The shell is a command-line interpreter that provides a user interface to an operating system's services. It allows users to interact with the system through text-based commands and scripts. Shell scripting refers to writing a series of commands in a script file to automate tasks and perform complex operations.
@ -17,6 +18,33 @@ command
Commands can be either a script, a binary or anything that can be executed. If you don't provide a full path to the file you want to run the shell will search in the locations defined in the `$PATH` environment variable. Commands can be either a script, a binary or anything that can be executed. If you don't provide a full path to the file you want to run the shell will search in the locations defined in the `$PATH` environment variable.
### Keyboard Shortcuts
- `Ctrl + C`: Terminate the current running process or command.
- `Ctrl + Z`: Suspend the current process and push it to the background.
- `Ctrl + D`: Exit the terminal or send EOF (End Of File) if running a script or command.
- `Ctrl + L`: Clear the terminal screen (similar to the clear command).
- `Ctrl + A`: Move the cursor to the beginning of the line.
- `Ctrl + E`: Move the cursor to the end of the line.
- `Ctrl + U`: Delete everything from the cursor position to the beginning of the line.
- `Ctrl + K`: Delete everything from the cursor position to the end of the line.
- `Ctrl + W`: Delete the word before the cursor.
- `Ctrl + R`: Search command history backward interactively.
- `Ctrl + T`: Swap the current character with the previous one (transpose).
- `Ctrl + Y`: Paste (yank) the last killed text.
- `Ctrl + P`: Previous command in history (similar to the Up arrow key).
- `Ctrl + N`: Next command in history (similar to the Down arrow key).
- `Alt + F`: Move forward one word.
- `Alt + B`: Move backward one word.
- `Alt + D`: Delete the word after the cursor.
- `Shift + PageUp/PageDown`: Scroll the terminal output up or down.
- `Tab`: Auto-complete file or directory names.
### Process Management
- `Ctrl + Z`: Suspend a running process.
- `fg`: Resume the last suspended process in the foreground.
- `bg`: Resume the last suspended process in the background.
- `jobs`: List all jobs currently running or suspended.
### Arguments ### Arguments
Everything after the command will be provided to the command as arguments. Each argument is separated by a space character. To avoid that you could quote an argument or escape the space character. Everything after the command will be provided to the command as arguments. Each argument is separated by a space character. To avoid that you could quote an argument or escape the space character.
@ -229,7 +257,7 @@ Assume variable **a** holds 10 and variable **b** holds 20 then −
| * (Multiplication) | Multiplies values on either side of the operator | `expr $a \* $b` will give 200 | | * (Multiplication) | Multiplies values on either side of the operator | `expr $a \* $b` will give 200 |
| / (Division) | Divides left hand operand by right hand operand | `expr $b / $a` will give 2 | | / (Division) | Divides left hand operand by right hand operand | `expr $b / $a` will give 2 |
| % (Modulus) | Divides left hand operand by right hand operand and returns remainder | `expr $b % $a` will give 0 | | % (Modulus) | Divides left hand operand by right hand operand and returns remainder | `expr $b % $a` will give 0 |
| = (Assignment) | Assigns right operand in left operand | `a = $b` would assign value of b into a | | = (Assignment) | Assigns right operand in left operand | `a = $b` would assign value of b into a |
| == (Equality) | Compares two numbers, if both are same then returns true. | `[$a == $b ]` would return false. | | == (Equality) | Compares two numbers, if both are same then returns true. | `[$a == $b ]` would return false. |
| != (Not Equality) | Compares two numbers, if both are different then returns true. | `[ $a != $b ]` would return true. | | != (Not Equality) | Compares two numbers, if both are different then returns true. | `[ $a != $b ]` would return true. |
@ -250,8 +278,8 @@ Assume variable **a** holds 10 and variable **b** holds 20 then −
##### Boolean Operators ##### Boolean Operators
Assume variable **a** holds 10 and variable **b** holds 20 then − Assume variable **a** holds 10 and variable **b** holds 20 then −
| Operator | Description | Example | | Operator | Description | Example |
| -------- | -------------------------------------------------------------------------------------------------------- | ------------------------------------- | | -------- | -------------------------------------------------------------------------------------------------------- | --------------------------------------- |
| **!** | This is logical negation. This inverts a true condition into false and vice versa. | `[ ! false ]` is true. | | **!** | This is logical negation. This inverts a true condition into false and vice versa. | `[ ! false ]` is true. |
| **-o** | This is logical **OR**. If one of the operands is true, then the condition becomes true. | `[ $a -lt 20 -o $b -gt 100 ]` is true. | | **-o** | This is logical **OR**. If one of the operands is true, then the condition becomes true. | `[ $a -lt 20 -o $b -gt 100 ]` is true. |
| **-a** | This is logical **AND**. If both the operands are true, then the condition becomes true otherwise false. | `[ $a -lt 20 -a $b -gt 100 ]` is false. | | **-a** | This is logical **AND**. If both the operands are true, then the condition becomes true otherwise false. | `[ $a -lt 20 -a $b -gt 100 ]` is false. |