There is a shell, there is a way…

This is the study notes about bash shell-scripting. In part I, I would like to cover basic commands for starters.

Prelude

I have a memory shortage condition and this is just to warm up my scripting skills. Don’t expect to explain things. If you have strong imagination,that might works.

Some Env Setup

alias

create shortcut to save your fingers

$ alias l='ls'
$ alias ll='ls -l'
$ alias c='cd'
$ alias cc='cd ..'

$ set completion-ignore-case On

fuck the case-sensitive

’#!/bin/bash’

this ‘#i’ is called shebang. Declares that you are start banging with bash.

Variables

like php,everything is with $ sign.

 echo $PATH
 dir=${PWD##*/} //nowhitespace
 echo "The current working directory is $dir" 

Read input

sometimes,you want variables from outside world.

echo -n “Enter your name: “
read myvar
echo “myvar is $myvar

Some more advanced reading

this is for smarty pant.

 while read message
do
	 echo $message
	sleep 1
	 date
 done < /etc/motd

Positional parameters

if you know how to count one two and three,you can do it!

$ cat params.sh

#!/bin/bash
echo “My name is `basename $0` - I was called as $0echo “My first parameter is: $1echo “My second parameter is: $2”
//try it
$ ./params.sh one two

Small bash program

This is a bash script that did something which makes sense.

#! /bin/sh

calculate the length of the hypotenuse of a Pythagorean triangle

using hypotenuse^2 = adjacent^2 + opposite^2

echo -n Enter the Adjacent length: 
read adjacent
echo -n Enter the Opposite length: 
read opposite
osquared=$(($opposite ** 2)) # get o^2
asquared=$(($adjacent ** 2)) # get a^2
hsquared=$(($osquered + $asquared)) # h^2 = a^2 + o^2
hypotenuse=`echo “scale=3;sqrt ($hsquared)” | bc` # bc does sqrt
echo “The Hypotenuse is $hypotenuse

###Wildcards

####Globbing It’s a term comes from global and it will searchs all trees from the whole forest.

ls A*
ls A??
ls *.txt
ls *.???
ls -ld /etc/rc{0,1,2,3,4,5,6}.d //create multiple file names rc0.d,rc1.d and so on
ls a[a-z]c.txt //list files name start with a and ends with c and any characters between a to z

Quoting

Not a big deal but minor issues are the thing that destory the most.

echo '*'
echo "*"
echo "this is a '*'"
echo 'this is a "*"'