---
title: Scripting
permalink: Linux/Scripting
category:  Linux
parent:   Linux
layout: default
has_children: false
share: true
shortRepo:
  - linux
  - default
---


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Table of contents
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1. TOC
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***

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# Variables

## Special Variables

### The name of the Bash script.

> ```$0```

### The first 9 arguments to the Bash script. (As mentioned above.)

> ```$1``` - ```$9```

### How many arguments were passed to the Bash script.

> ```$#```

### All the arguments supplied to the Bash script.

> ```$@```

### The exit status of the most recently run process.

> ```$?```

### The process ID of the current script.

> ```$$```

### The username of the user running the script.

> ```$USER```

### The hostname of the machine the script is running on.

> ```$HOSTNAME```

### The number of seconds since the script was started.

> ```$SECONDS```

### Returns a different random number each time is it referred to.

> ```$RANDOM```

### Returns the current line number in the Bash script.

> ```$LINENO```

## Use

### The first, second, etc command line arguments to the script.

> ```$1, $2, ...```

### To set a value for a variable. Remember, no spaces on either side of =

> ```variable=value```

### Double will do variable substitution, single will not.

> ```Quotes " '```

### Save the output of a command into a variable

> ```variable=$( command )```

### Make the variable var1 available to child processes.

> ```export var1```

# Std In and Out

## use a string put int script that needs a user response

```shell
export GH_TOKEN=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;
act=$(gh auth status -t >>(tee -a) 2>&1 | sed -n 's/.*Token: //p');
if [[ "$act" == *"$GH_TOKEN"* ]]
then echo $GH_TOKEN | gh auth login --with-token;  
```

## use output from a script to set a variable

> ```tee``` can be used to create a file from output

`here i take the out put pipe that and error output`

```shell
 2 >&1
```

> File descriptor 1

`is the standard output (stdout)`

> File descriptor 2

`is the standard error (stderr)`

> ```2>``` redirects stderr to an (unspecified) file.

> ```&1``` redirects ```stderr``` to ```stdout```