Shells

Back to Basics

User interface for accessing the operating system's services.

(I got that from wikipedia)

Another simple way to put it is:

- A program that takes in user input and has the OS perform the tasks.

This is the most basic it can get, not used as much, but still used in someplaces.

Places I have seen it used before:

• docker images
• when writing shell scripts

This is what most are familar with

Bourne again shell

- Very similar to shell with some more added features.

- Since it has been made freely available for everyone, it has become a standard that a lot of people use.

It is an "upgraded" version of bash, with some feature built in improvements, i.e. tab complete commands.

Here are some notable frameworks that make it easier to use:

oh-my-zsh

prezto

This is similar to zsh, but a lot of the customization is already done for you.

There are a lot more but these are the more "popular" ones that I am aware of, there are also:

• command shell/powershell (windows)
• KSH (which was developed by AT&T)
• CSH (made scripts look more like the C language)

We will talk about how we can start using these shells or rather what kind of information we can get.

'#!/bin/sh'

What is it?

#!

shebang

hashbang

poundbang

hashpling

(I also pulled these from wikipedia)

#!

Basicly says which interpreter to use.

#!/bin/bash

#!/bin/sh

#!/bin/csh

#!/usr/bin/perl

#!/path/to/interpreter

When trying to run a script (./scriptname) you are usually unable to run it at first.

The reason being, you usually don't have permission to.

               
               ls
               
              

               
CCLulu∴~/workspace/shell-basics⨕master⚡
 ⤕  ls
CONTRIBUTING.md   Gruntfile.js      LICENSE           README.md         bower.json        css               demo.html         index.html        js                lib               node_modules      package-lock.json package.json      plugin            res
               
              

               
               ls -la
               
              

               
CCLulu∴~/workspace/shell-basics⨕master⚡
 ⤕  ls -la
total 496
drwxr-xr-x   21 Cuahuc  staff     672 Feb  5 13:24 .
drwxr-xr-x   44 Cuahuc  staff    1408 Feb  5 09:44 ..
-rw-r--r--@   1 Cuahuc  staff    8196 Feb  5 13:08 .DS_Store
drwxr-xr-x   12 Cuahuc  staff     384 Feb  5 13:09 .git
-rw-r--r--    1 Cuahuc  staff     142 Feb  5 07:48 .gitignore
-rw-r--r--    1 Cuahuc  staff      75 Feb  5 07:48 .travis.yml
-rw-r--r--    1 Cuahuc  staff    1062 Feb  5 07:48 CONTRIBUTING.md
-rw-r--r--    1 Cuahuc  staff    3749 Feb  5 07:48 Gruntfile.js
-rw-r--r--    1 Cuahuc  staff    1103 Feb  5 07:48 LICENSE
-rw-r--r--    1 Cuahuc  staff     226 Feb  5 08:27 README.md
-rw-r--r--    1 Cuahuc  staff     512 Feb  5 07:48 bower.json
drwxr-xr-x    6 Cuahuc  staff     192 Feb  5 07:48 css
-rw-r--r--    1 Cuahuc  staff   16240 Feb  5 07:48 demo.html
-rw-r--r--    1 Cuahuc  staff    7828 Feb  5 13:24 index.html
drwxr-xr-x    4 Cuahuc  staff     128 Feb  5 08:28 js
drwxr-xr-x    5 Cuahuc  staff     160 Feb  5 07:48 lib
drwxr-xr-x  466 Cuahuc  staff   14912 Feb  5 07:51 node_modules
-rw-r--r--    1 Cuahuc  staff  182915 Feb  5 07:51 package-lock.json
-rw-r--r--    1 Cuahuc  staff    1066 Feb  5 07:48 package.json
drwxr-xr-x   11 Cuahuc  staff     352 Feb  5 07:48 plugin
drwxr-xr-x    4 Cuahuc  staff     128 Feb  5 09:19 res
               
              

Why do this?

               
-rw-r--r--    1 Cuahuc  staff    7828 Feb  5 13:24 index.html
drwxr-xr-x    4 Cuahuc  staff     128 Feb  5 08:28 js
               
              

Let's break it down

               
   r w x
   1 1 1 = 7
   1 1 0 = 6
   1 0 1 = 5
   1 0 0 = 4
   0 1 1 = 3
   0 1 0 = 2
   0 0 1 = 1
   0 0 0 = 0
               
              

                
User Group World
rwx  rwx   rwx
                
              

                
r w x | r w x |  r w x
1 1 1 | 1 1 1 |  1 1 1 = 777
1 1 1 | 1 0 1 |  1 0 1 = 755
1 1 1 | 1 0 0 |  1 0 0 = 744
                
              

               
-rw-r--r--    1 Cuahuc  staff    7828 Feb  5 13:24 index.html
drwxr-xr-x    4 Cuahuc  staff     128 Feb  5 08:28 js
               
              

                
r w x | r w x |  r w x
1 1 1 | 1 0 1 |  1 0 1 = 755
1 1 0 | 1 0 0 |  1 0 0 = 644
                
              

Changing permissions

A simple command to change your file's permission:

               
               chmod 777 filename.sh
               chmod 755 filename.sh
               chmod 744 filename.sh
               
              

Great, but how do I run it from anywhere?

Put in the PATH!

Is the place where your OS looks for where to run the binary

              
              echo $PATH
              
            

              
/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/localadmin/bin:/Users/cuahuctemocosorio/bin:/Users/cuahuctemocosorio/go/bin
              
            

Last bit, some keyboard short cuts.

               
               ctrl + a // jump to the beginning of the line
               ctrl + e // jump to the end of the line
               ctrl + u // clear the current line
               ctrl + w // clear one word behind the cursor
               ctrl + l // clear the terminal screen
               ctrl + n // same as up arrow
               ctrl + p // same as down arrow
               ctrl + f // move forward one character
               ctrl + b // move back one character