Bash Notes

Parameters

A parameter is an entity that stores values

There are three types of parameters:

1. positional parameters
   • The arguments on the command line are available to a shell program as numbered parameters.
   • for example: $1 depicts the first command line argument
2. special parameters
3. variables name=VALUE
   • Bash is very particular about spacing: not that there are no spaces before the '=' and none after.

• Add -e to the echo command if the escape sequences are to recognised.

Ask the user for input

if we would like to ask the user for input then we use a command called read. This command takes the input and will save it into a variable.

#! /bin/bash
echo Hello, who am I talking to ?

read varname

echo It\'s nice to meet you $varname

More with Read

we can alter the behaviour of read with a variety of command line options.Two commanly used options however are -p which allows you to specify a prompt and -s which makes the input silent.

This can make it easy to ask for a username and password combination

#! /bin/bash

read -p 'Username: ' uservar
read -sp 'Password: ' passvar
echo
echo login details accepted

More variables

#! /bin/bash

echo What books do you like?

read game1 game2 game3

echo games are: $game1 $game2 $game3

• dirs -v
• $@ --> depicts the entire string of the args
• $1 --> depicts the first word of the args # args[0]
• -z --> returns true if the string is empty