Upgrade according 25th meeting

Bash.md

@@ -14,7 +14,7 @@ _paginate: false
 Introduction to Bash Scripting<!--fit-->
 ===
 
-https://gogs.elic.ucl.ac.be/pbarriat/learning-bash
+https://forge.uclouvain.be/barriat/learning-bash
 
 ![h:200](assets/bash_logo.png)
 
@@ -131,6 +131,10 @@ 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)
 > combination of `bash #` and `bang !`
 
+
+
+---
+
 ### Comments start with `#`
 
 On a line, any characters after `#` will be ignored -- *with the exception of* `#!`
@@ -140,13 +144,13 @@ echo "A comment will follow." # Comment here.
 #                            ^ Note whitespace before #
 ```
 
----
-
 ### There is no standard indentation
 
 - Pick a standard in your team that you can all work to
 - Use something your editor makes easy (**Vim** uses `Tab`)
 
+---
+
 ### Command separators
 
 Commands can be combined using **meta-characters** and **control operators**
@@ -176,6 +180,10 @@ $ cd myfolder || ls  # if failed cd to myfolder, `ls` will run
 
 ---
 
+# Hands-on exercise
+
+---
+
 # Variables and data types in Bash
 
 Variables let you store data : **numeric values** or **character(s)**
@@ -190,11 +198,11 @@ Set the variable values in the following ways :
 - access the variable value using `$`: `echo $greeting`
 - assign based on variable: `b=$a`
 
-  > !!! no space before or after `=` in the assignation !!!
-  > `myvar=Hello World` :boom: `-bash: World: command not found`
-
 ---
 
+**!!!** no space before or after `=` in the assignation **!!!**
+> `myvar=Hello World` :boom: `-bash: World: command not found`
+
 ### Quotes for character(s) `" '`
 
 Double will do variable substitution, single will not
@@ -207,16 +215,6 @@ Double will do variable substitution, single will not
 myvar=$( ls )
 ```
 
-### Export variables
-
-```bash 
-#!/bin/bash
-var1=blah
-# Make the variable `var1` available to child processes
-export var1
-./script2.sh
-```
-
 ---
 
 ## Variable naming conventions
@@ -237,20 +235,6 @@ export var1
 
 ---
 
-|  Special Variables    |         |
-| ------------ | --------------- |
-|     `$0`    |  the name of the script |
-|     `$1` - `$9` | the first 9 arguments |
-|     `$#`    |  how many arguments were passed |
-|     `$@`    |  all the arguments supplied |
-|     `$$`    |  the process ID of the current script |
-|     `$?`    |  the exit status of the most recently run process |
-|     `$RANDOM`    |  returns a random number |
-|     `$LINENO`    |  returns the current line number |
-|     `$SECONDS`    | the number of seconds since the script was started |
-
----
-
 # Arithmetic
 
 |  Operator    |     Operation   |
@@ -288,7 +272,7 @@ a=$( expr 10 - 3 )
 ```
 
 - double parentheses : return the result of the expression
-  > it is the preferred method
+  > it is the **preferred method**
 
 ---
 
@@ -336,18 +320,17 @@ fi
 ### `test` command 
 
 ```bash 
-test -s /proc/cpuinfo
-echo $?
+test -s /etc/hosts && echo "Exists and not empty"
 ```
 
 |  Operator    |     Description   |
 | ------------ | --------------- |
 | `-d FILE` 	            |  FILE exists and is a directory                            |
 | `-e FILE` 	            |  FILE exists                                                        |
-| `-r FILE` 	            |  FILE exists and the read permission is granted                      |      
-| `-s FILE` 	            |  FILE exists and it's size is greater than zero (ie. it is not empty)|
-| `-w FILE` 	            |  FILE exists and the write permission is granted                     |       
-| `-x FILE` 	            |  FILE exists and the execute permission is granted                   |   
+| `-s FILE` 	            |  FILE exists and it's size is greater than zero (ie. it is **not empty**)|
+| `-r FILE` 	            |  FILE exists and the read permission is granted                      |   
+
+> `-w` and `-x` test the write and the execute permission
 
 ---
 
@@ -409,6 +392,10 @@ esac
 
 ---
 
+# Hands-on exercise
+
+---
+
 # Arrays
 
 ### Indexed arrays
@@ -456,8 +443,7 @@ unset countries[BHR]
 echo ${countries[@]}
 ```
 
----
-
+<!-- 
 ### About `declare`
 
 ```bash
@@ -472,6 +458,7 @@ Examples :
 - force a character(s) variable to store all uppercase or lowercase letters
 - display the attributes and values of all variables
 - etc.
+-->
 
 ---
 
@@ -543,6 +530,8 @@ 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
@@ -554,11 +543,15 @@ do
 done < "$input"
 ```
 
-The internal field separator (`IFS`) is set to the empty string to preserve whitespace issues
-
 > 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
+-->
 
 ---
 
@@ -580,6 +573,10 @@ done
 
 ---
 
+# Hands-on exercise
+
+---
+
 # Arguments - Positional Parameters
 
 How to pass command-line arguments to a bash script ?
@@ -607,6 +604,17 @@ a b c d e
 
 ---
 
+|  Special Variables    |         |
+| ------------ | --------------- |
+|     `$0`    |  the name of the script |
+|     `$1` - `$9` | the first 9 arguments |
+|     `$#`    |  how many arguments were passed |
+|     `$@`    |  all the arguments supplied |
+|     `$$`    |  the process ID of the current script |
+|     `$?`    |  the exit status of the most recently run process |
+
+---
+
 ### Flags
 
 ```bash
@@ -668,7 +676,7 @@ date
 echo $?
 ```
 
-> [List of common exit codes for GNU/Linux](https://slg.ddnss.de/list-of-common-exit-codes-for-gnu-linux/)
+> [List of special exit codes for GNU/Linux](https://tldp.org/LDP/abs/html/exitcodes.html)
 
 ---
 
@@ -812,6 +820,10 @@ ls
 
 ---
 
+# Hands-on exercise
+
+---
+
 # Shell vs Environment Variables
 
 Consider the script `test.sh` below :
@@ -957,6 +969,10 @@ time ./manager_par.sh
 
 ---
 
+# Hands-on exercise
+
+---
+
 # Debug
 
 Tips and techniques for debugging and troubleshooting Bash scripts