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Valider 15629a0c rédigé par Jérôme de Favereau de Jeneret's avatar Jérôme de Favereau de Jeneret
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first part of updates

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1 requête de fusion!1Add exercises, some edits
...@@ -80,6 +80,7 @@ echo $STRING ...@@ -80,6 +80,7 @@ echo $STRING
--- ---
<!-- JDF: je pense qu c'est trop tôt pur cette info
# Shell syntax rules # Shell syntax rules
Shells use 3 **"standard I/O streams"** Shells use 3 **"standard I/O streams"**
...@@ -93,19 +94,21 @@ Shell has several **meta-characters** and **control operators** ...@@ -93,19 +94,21 @@ Shell has several **meta-characters** and **control operators**
> `|`, `&`, `>`, `;` , etc. > `|`, `&`, `>`, `;` , etc.
--- ---
-->
# Bash environment # Bash environment
In a Bash shell many things constitute your environment In a Bash shell many things constitute your environment
- the form of your prompt - the form of your 'prompt' (what comes left of your commands)
- your home directory and your working directory - your home directory and your working directory
- the name of your shell - the name of your shell
- functions that you have defined - functions that you have defined
- etc. - etc.
Environment includes many variables that may have been set **by bash** or **by you** Environment includes many variables that may have been set **by bash** or **by you**
> Access the value of a variable by prefixing its name with `$`
**Access the value of a variable by prefixing its name with `$`**
--- ---
...@@ -119,8 +122,11 @@ Environment includes many variables that may have been set **by bash** or **by y ...@@ -119,8 +122,11 @@ Environment includes many variables that may have been set **by bash** or **by y
| `SHELL` | the name of the shell | | `SHELL` | the name of the shell |
| `UID` | the numeric user id of the logged-in user | | `UID` | the numeric user id of the logged-in user |
So to get the value of `USER` you would use `$USER` in bash code
> You can use special files to control bash variables : `$HOME/.bashrc` > You can use special files to control bash variables : `$HOME/.bashrc`
--- ---
# Bash Scripting basics # Bash Scripting basics
...@@ -131,13 +137,15 @@ By naming convention, bash scripts end with `.sh` ...@@ -131,13 +137,15 @@ By naming convention, bash scripts end with `.sh`
A good practice is to define a `shebang` : first line of the script, `shebang` is simply an absolute path to the shell interpreter (see `echo $SHELL` result) A good practice is to define a `shebang` : first line of the script, `shebang` is simply an absolute path to the shell interpreter (see `echo $SHELL` result)
> combination of `bash #` and `bang !` > combination of `bash #` and `bang !`
The usual shebang for bash is `#!/bin/bash`
--- ---
### Comments start with `#` ### Comments start with `#`
On a line, any characters after `#` will be ignored -- *with the exception of* `#!` On a line, any characters after `#` will be ignored (with the exception of `#!`)
```bash ```bash
echo "A comment will follow." # Comment here. echo "A comment will follow." # Comment here.
...@@ -150,7 +158,7 @@ echo "A comment will follow." # Comment here. ...@@ -150,7 +158,7 @@ echo "A comment will follow." # Comment here.
- Use something your editor makes easy (**Vim** uses `Tab`) - Use something your editor makes easy (**Vim** uses `Tab`)
--- ---
<!-- JDF: je pnseque c'est trop tôt pour ceci
### Command separators ### Command separators
Commands can be combined using **meta-characters** and **control operators** Commands can be combined using **meta-characters** and **control operators**
...@@ -167,11 +175,11 @@ $ cd myfolder || ls # if failed cd to myfolder, `ls` will run ...@@ -167,11 +175,11 @@ $ cd myfolder || ls # if failed cd to myfolder, `ls` will run
``` ```
--- ---
-->
# Permissions and execution # Permissions and execution
- Bash script is nothing else just a **text file** containing instructions to be executed sequentially - Bash script is nothing else just a **text file** containing instructions to be executed sequentially
> by default in Linux, a new text file is **-rw-r--r--** (or 644) > by default in Linux, a new text file's permissons are **-rw-r--r--** (or 644)
- You can run the script `hello_world.sh` using - You can run the script `hello_world.sh` using
* `sh hello_world.sh` * `sh hello_world.sh`
* `bash hello_world.sh` * `bash hello_world.sh`
...@@ -182,6 +190,15 @@ $ cd myfolder || ls # if failed cd to myfolder, `ls` will run ...@@ -182,6 +190,15 @@ $ cd myfolder || ls # if failed cd to myfolder, `ls` will run
# Hands-on exercise # Hands-on exercise
Your first bash script:
1. create a folder `bash_exercises` and go there
1. use your favourite editor (vim, obviously) to create a new file called `exercise_1.sh`
1. write some code in it to display the current working directory as:
> The current directory is : /home/me/bash_exercises
4. make the file executable
5. run it !
--- ---
# Variables and data types in Bash # Variables and data types in Bash
...@@ -190,22 +207,29 @@ Variables let you store data : **numeric values** or **character(s)** ...@@ -190,22 +207,29 @@ Variables let you store data : **numeric values** or **character(s)**
You can use variables to read, access, and manipulate data throughout your script You can use variables to read, access, and manipulate data throughout your script
**There are no data types in Bash** **You don't specify data types in Bash**
Set the variable values in the following ways :
- assign directly : `greeting="Welcome"` or `a=4` - assign directly : `greeting="Welcome"` or `a=4`
- access the variable value using `$`: `echo $greeting`
- assign based on variable: `b=$a` - assign based on variable: `b=$a`
--- And then access using `$`: `echo $greeting`
**!!!** no space before or after `=` in the assignation **!!!** **!!!** no space before or after `=` in the assignation **!!!**
> `myvar=Hello World` :boom: `-bash: World: command not found` `myvar = "Hello World"` :boom:
---
### Quotes for character(s) `" '` ### Quotes for character(s) `" '`
Double will do variable substitution, single will not Double will do **variable substitution**, single will not:
```
$ echo "my home is $HOME"
my home is /home/me
$ echo 'my home is $HOME'
my home is $HOME
```
### Command Substitution ### Command Substitution
...@@ -231,7 +255,7 @@ myvar=$( ls ) ...@@ -231,7 +255,7 @@ myvar=$( ls )
* Avoid using **reserved keywords**, such as `if`, `then`, `else`, `fi`, and so on... * Avoid using **reserved keywords**, such as `if`, `then`, `else`, `fi`, and so on...
* **Never** name your private variables using only **UPPERCASE** characters * **Never** name your private variables using only **UPPERCASE** characters to avod conflicts with builtins
--- ---
...@@ -242,13 +266,16 @@ myvar=$( ls ) ...@@ -242,13 +266,16 @@ myvar=$( ls )
| `+` `-` `\*` `/` | addition, subtraction, multiply, divide | | `+` `-` `\*` `/` | addition, subtraction, multiply, divide |
| `var++` | increase the variable var by 1 | | `var++` | increase the variable var by 1 |
| `var--` | decrease the variable var by 1 | | `var--` | decrease the variable var by 1 |
| `%` | modulus (Return the remainder after division) | | `%` | modulus (remainder after division) |
Several ways to go about arithmetic in Bash scripting : Several ways to go about arithmetic in Bash scripting :
`let`, `expr` or using **double parentheses** `let`, `expr` or using **double parentheses**
<!-- JDF: probablement pas la bonne place pour ça
Return the length of a variable : `${#var}` Return the length of a variable : `${#var}`
-->
<!-- JDF: a mon avis pas utile
--- ---
- `let` make a variable equal to an expression - `let` make a variable equal to an expression
...@@ -273,7 +300,7 @@ a=$( expr 10 - 3 ) ...@@ -273,7 +300,7 @@ a=$( expr 10 - 3 )
- double parentheses : return the result of the expression - double parentheses : return the result of the expression
> it is the **preferred method** > it is the **preferred method**
-->
--- ---
```bash ```bash
...@@ -298,6 +325,23 @@ echo $b # 16 ...@@ -298,6 +325,23 @@ echo $b # 16
# Conditional statements # Conditional statements
Use:
* `if condition; then` to start conditional block
* `else` to start alternative block
* `elif` to start alternative conition block
* `fi` to close conditional block
The following operaors can be used beween conditions:
* `||` means **OR**
* `&&` mean **AND**
---
# Conditional exemple
(Dont pay too much attention to the details yet)
```bash ```bash
#!/bin/bash #!/bin/bash
echo "Please enter a number: " echo "Please enter a number: "
...@@ -313,14 +357,28 @@ else ...@@ -313,14 +357,28 @@ else
fi fi
``` ```
> read the **standard input stream** with the `read` command Read the **standard input stream** with the `read` command
--- ---
### `test` command | Operator | Description |
| ------------ | --------------- |
| `! EXPRESSION` | The EXPRESSION is false|
| `-n STRING` | The length of STRING is greater than zero |
| `-z STRING` | The lengh of STRING is zero (ie it is empty) |
| `STR1 = STR2` | STRING1 is equal to STRING2 |
| `STR1 != STR2` | STRING1 is not equal to STRING2 |
| `INT1 -eq INT2` | INTEGER1 is numerically equal to INTEGER2 (or `==`) |
| `INT1 -gt INT2` | INTEGER1 is numerically greater than INTEGER2 |
| `INT1 -lt INT2` | INTEGER1 is numerically less than INTEGER2 |
| `INT1 -ne INT2` | INTEGER1 is numerically not equal to INTEGER2 |
---
### Build conditions with the `test` command
```bash ```bash
test -s /etc/hosts && echo "Exists and not empty" test -s /etc/hosts
``` ```
| Operator | Description | | Operator | Description |
...@@ -334,20 +392,6 @@ test -s /etc/hosts && echo "Exists and not empty" ...@@ -334,20 +392,6 @@ test -s /etc/hosts && echo "Exists and not empty"
--- ---
| Operator | Description |
| ------------ | --------------- |
| `! EXPRESSION` | The EXPRESSION is false|
| `-n STRING` | The length of STRING is greater than zero |
| `-z STRING` | The lengh of STRING is zero (ie it is empty) |
| `STR1 = STR2` | STRING1 is equal to STRING2 |
| `STR1 != STR2` | STRING1 is not equal to STRING2 |
| `INT1 -eq INT2` | INTEGER1 is numerically equal to INTEGER2 (or `==`) |
| `INT1 -gt INT2` | INTEGER1 is numerically greater than INTEGER2 |
| `INT1 -lt INT2` | INTEGER1 is numerically less than INTEGER2 |
| `INT1 -ne INT2` | INTEGER1 is numerically not equal to INTEGER2 |
---
### Conditional: light variation ### Conditional: light variation
Check an expression in the `if` statement ? Check an expression in the `if` statement ?
...@@ -394,6 +438,13 @@ esac ...@@ -394,6 +438,13 @@ esac
# Hands-on exercise # Hands-on exercise
1. In your `bash_exercises` folder create a new bash file called `exercise_2.sh` and make it executable
2. Ask the user for two numbers smaller or equal to 100, put them in variables `NUMBER1` and `NUMBER2`
3. Do the following only if the number are smaller than 100:
4. Check if at least one of the numbers is a multiple of 3, and tell the user
5. Otherwise, check if both numbers are even, and tell the user
6. If the user's numbers ar too big, tell them
--- ---
# Arrays # Arrays
...@@ -401,7 +452,6 @@ esac ...@@ -401,7 +452,6 @@ esac
### Indexed arrays ### Indexed arrays
```bash ```bash
#!/bin/bash
# Declare an array with 4 elements # Declare an array with 4 elements
my_array=( 'Debian Linux' 'Redhat Linux' Ubuntu OpenSUSE ) my_array=( 'Debian Linux' 'Redhat Linux' Ubuntu OpenSUSE )
# get number of elements in the array # get number of elements in the array
...@@ -423,16 +473,16 @@ echo ${my_array[@]} ...@@ -423,16 +473,16 @@ echo ${my_array[@]}
By default, a bash array is an indexed array : need to use the `declare` command By default, a bash array is an indexed array : need to use the `declare` command
```bash ```bash
#!/bin/bash declare -A acronyms # -A for associative array
declare -A acronyms
acronyms[ACK]=Acknowledgement acronyms[ACK]=Acknowledgement
acronyms[EOF]="End of Frame" acronyms[EOF]="End of Frame"
echo ${acronyms[ACK]} echo ${acronyms[ACK]}
if [ ${acronyms[EOF]+_} ]; then echo "Found"; else echo "Not found"; fi if [ ${acronyms[EOF]+_} ]; then echo "Found"; else echo "Not found"; fi
``` ```
The variable expansion `${MYVAR+ABC}` expands to "ABC" is `MYVAR` is set and to nothing otherwise.
```bash ```bash
#!/bin/bash
declare -A countries=( [ALB]=Albania [BHR]=Bahrain [CMR]=Cameroon [DNK]=Denmark [EGY]=Egypt ) declare -A countries=( [ALB]=Albania [BHR]=Bahrain [CMR]=Cameroon [DNK]=Denmark [EGY]=Egypt )
echo ${countries[@]} echo ${countries[@]}
echo ${!countries[@]} echo ${!countries[@]}
...@@ -484,7 +534,6 @@ Basic loop structures in Bash scripting : ...@@ -484,7 +534,6 @@ Basic loop structures in Bash scripting :
### Examples ### Examples
```bash ```bash
#!/bin/bash
# Basic while loop # Basic while loop
counter=0 counter=0
while [ $counter -lt 3 ]; do while [ $counter -lt 3 ]; do
...@@ -493,7 +542,6 @@ while [ $counter -lt 3 ]; do ...@@ -493,7 +542,6 @@ while [ $counter -lt 3 ]; do
done done
``` ```
```bash ```bash
#!/bin/bash
# Basic until loop # Basic until loop
counter=1 counter=1
until [ $counter -gt 10 ]; do until [ $counter -gt 10 ]; do
...@@ -530,31 +578,6 @@ for i in $( cat file.txt ) ...@@ -530,31 +578,6 @@ for i in $( cat file.txt )
--- ---
### How to Read a File Line By Line
```bash
#!/bin/bash
# How to Read a File Line By Line
input="/path/to/txt/file"
while IFS= read -r line
do
echo "$line"
done < "$input"
```
> by default `read` removes all leading and trailing whitespace characters such as spaces and tabs
<!--
`while IFS= read -r line`
The internal field separator (`IFS`) is set to the empty string to preserve whitespace issues
The `-r` option is used not to allow backslashes to escape any characters
-->
---
```bash ```bash
#!/bin/bash #!/bin/bash
# How to iterate over keys or values of an Array # How to iterate over keys or values of an Array
...@@ -575,6 +598,15 @@ done ...@@ -575,6 +598,15 @@ done
# Hands-on exercise # Hands-on exercise
Speed game:
1. Use the following webiste to get a list of random words: https://randomwordgenerator.com and put them in a variable
2. Register the start time with `date +%s` and put it in a variable `TSTART`
3. Loop over the words and ask the user to give the number of letters. Put the answers in an associative array using the words as keys and the answers as values
4. Register the end time in `TEND`
5. Display the total run time
6. Loop over the associative array to compute the score (number of good answers) and show it to the user.
--- ---
# Arguments - Positional Parameters # Arguments - Positional Parameters
...@@ -660,6 +692,31 @@ cat $1 2>&1 ...@@ -660,6 +692,31 @@ cat $1 2>&1
--- ---
### How to Read a File Line By Line : input redirection
```bash
#!/bin/bash
# How to Read a File Line By Line
input="/path/to/txt/file"
while IFS= read -r line
do
echo "$line"
done < "$input"
```
> by default `read` removes all leading and trailing whitespace characters such as spaces and tabs
<!--
`while IFS= read -r line`
The internal field separator (`IFS`) is set to the empty string to preserve whitespace issues
The `-r` option is used not to allow backslashes to escape any characters
-->
---
# Return codes # Return codes
Linux command returns a status when it terminates normally or abnormally Linux command returns a status when it terminates normally or abnormally
......
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