> For the complete documentation index, see [llms.txt](https://explore-vineeth.gitbook.io/mywiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://explore-vineeth.gitbook.io/mywiki/programming/bash.md).

# Bash

There are various types of  shells available. bash, csh, zsh.

### Shebang

If we execute the script ./script.sh , it needs to have first line mentioning the interpretor.\
*<mark style="color:green;">#!/bin/bash</mark>* or *<mark style="color:green;">#!/bin/csh</mark>*&#x20;

Users can specify all "set" options along with the shell interpretor

### Execution

* /bin/sh is the default executor. it generally points to any of the above shell.\
  it is used by all make command executions. It is important to change the default shell&#x20;
* By default the env gets sourced. To get new shell without any user/system env.\
  /bin/bash --norc

### set options

* Printing each line before executing. ( set -x ) to unset ( set +x)&#x20;
* By default shell execution moves further even though a particular command gets failed.\
  To change this behaviour we need to use ( set -e )

### Non Interactive Mode

There is a difference in the execution between normal shell executin and using pipe with tee command. The animating commands changes its ourput based on this mode. \
Ex- see the yocto bitbake command normally and check the output with pipe and tee command

set flags can be used to toggle the modes ( setops )&#x20;

## Interpolation&#x20;

By default the variable gets substituted at the time of parsing. It will not allow to change the dependent variable.#Defining some variables

```bash
var_a="value-a"
var_b="value-b"
var_c='${var_a}/test'
# if we define var_c="${var_a}/test", it will substitue var_c="value-a/test" at the
# time of parsing
# Any further changes in var_a at later point will not get impacted on var_c
# var_c will always print "value-a/tets"

function parse_var() {
        local var=$1
        local val=$(eval "echo ${var}")
        echo ${val}
}

# Interpolate value of var_c -> var_a -> value-a
echo $var_c
parsed_var_c=$(parse_var $var_c)
echo ${parsed_var_c}

# Change the value of var_a
var_a="value-a-new"
echo $var_c
echo $(parse_var $var_c)

```

Pipes

#### <mark style="color:blue;">Clear Broken Shell</mark>

```bash
stty sane
```

## Useful libraries

assert functions&#x20;

## Coding Tips

```bash
#Usage of or in single line conditional statements
value = var1 || var2

```