notes/compsci-missing_semester_2020

ronny abraham 21f0424e48 updates

2024-12-12 18:30:39 +02:00

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lesson 02 | course overview + the shell

Links
- timestamps
Notes
- bash
  - spaces are critical with bash
  - quotes
- sequential execution

Links

timestamps

Notes

bash

spaces are critical with bash

this works:

foo=bar
echo $foo

this doesn't:

foo = bar
echo $foo

the output of that will be zsh: command not found: foo
what happens in the above example is that we are effectively calling the "foo" program with the arguments: "=" and "bar"

quotes

you can use double or single quotes to print a value
```
echo "Hello"
```
```
echo 'Hello'
```
double quotes can interpolate variables
```
echo "Value is $foo"
```
will return: Value is bar
single quotes can NOT interpoloate variables
```
echo 'Value is $foo'
```
will return: Value is $foo

sequential execution

bash functions

mcd.sh

mcd() {
        mkdir -p "$1"
        cd "$1"
        }

creates a function that can be executed after loading
- $1 is a global variable referring to the first parameter

source

using source mcd.sh source mcd.sh
then carry out the function mcd testdir
this will create a new directory and cd into it as per the definied functioned

variables

$0 – name of the script we are currently in
- if you run this in the shell it will display 'bash'
$1->$9 – the first through ninth argument given to a script
$? – the last error message
$_ — last argument of the previous call
!! – recreates the last call with it's arguments
- use with sudo if you found your call needed a sudo and you don't feel like retyping it again
```
ls -lah
sudo !!
```