Merge branch 'master' into 'master'

Exercice 5 + quelques changements de formulation

See merge request !4

Bash.md

@@ -34,7 +34,7 @@ It's called the **C**ommand **L**ine **U**ser **I**nterface
 **CLUI** is one of the many strengths of Linux :
 
 - allows to be independent of distros (or UNIX systems like OSX)
-- allows to easily work at distance (SSH)
+- allows to easily work remotely (SSH)
 - allows to join together simple (and less simple) commands to do complex things and automate **= scripting**
 
 In Linux, process automation relies heavily on scripting. This involves creating a file containing a series of commands that can be executed together
@@ -43,7 +43,7 @@ In Linux, process automation relies heavily on scripting. This involves creating
 
 # Linux Shell
 
-A **shell** is a program that takes commands from the keyboard and gives them to the operating system to perform
+A **shell** is a program that takes commands from the keyboard and transmits them to the operating system to perform
 
 The main function is to interpret your commands **= language**
 
@@ -92,8 +92,6 @@ In a Bash shell many things constitute your environment
 
 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 `$`**
-
 ---
 
 # Environment variables
@@ -106,6 +104,8 @@ Environment includes many variables that may have been set **by bash** or **by y
 |     `SHELL`    |  the name of the shell |
 |     `UID`    |  the numeric user id of the logged-in user |
 
+**Access the value of a variable by prefixing its name with `$`**
+
 So to get the value of `USER` you would use `$USER` in bash code
 
 > You can use special files to control bash variables : `$HOME/.bashrc`
@@ -142,7 +142,7 @@ echo "A comment will follow." # Comment here.
 - Use something your editor makes easy (**Vim** uses `Tab`)
 
 ---
-<!-- JDF: je pnseque c'est trop tôt pour ceci
+<!-- JDF: je pense que c'est trop tôt pour ceci
 ### Command separators
 
 Commands can be combined using **meta-characters** and **control operators**
@@ -335,7 +335,7 @@ echo $b # 16
 Use:
 * `if condition; then` to start conditional block
 * `else` to start alternative block
-* `elif` to start alternative conition block
+* `elif` to start alternative condition block
 * `fi` to close conditional block
 
 The following operaors can be used beween conditions:
@@ -442,7 +442,7 @@ esac
 # 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`
+2. Ask the user for two numbers smaller than 100 and put them in variables `NUMBER1` and `NUMBER2`
 
    > ```bash
    > #!/bin/bash
@@ -452,7 +452,7 @@ esac
 
 3. Check if the numbers are smaller than 100
    - If yes, check if both numbers are even and tell the user
-   - If not, tell the user with `echo 'my message'`
+   - If not, tell the user (use `echo`)
 
 ---
 
@@ -690,8 +690,6 @@ Shells use 3 standard I/O streams
 
 Shell has several **meta-characters** and **control operators** 
 
-> `|`, `&`, `>`, `;`, `<`, etc.
-
 ---
 
 # Control operators
@@ -814,7 +812,7 @@ _files="$@"
 * "small script within a script" that you may call multiple times 
 * great way to reuse code
 * a function is most reuseable when it performs a single task
-* good to put ancillary tasks within functions : logically separate from main
+* good to put ancillary tasks within functions : logically separate from main code
 
 ```bash
 #!/bin/bash
@@ -883,6 +881,9 @@ my_function
 echo $func_result
 ```
 
+<!-- Note JDF: est-ce que la partie ci-dessus est utile ? Autant montrer directement la bonne manière pour moi
+-->
+
 * Better way is to send the value to `stdout` using `echo`
 
 ```bash
@@ -908,18 +909,18 @@ print_something () {
 print_something Mars
 ```
 
-> Be careful in case of "overriding commands": plaese never use an existing linux command name.
+> Athough it is possible, you should try to avoid having functions using the name of existing linux commands.
 
 ---
 
 # Hands-on exercise
 
-1. Write a script called `exercise_5.sh` expecting **2 arguments**. If not exactly two arguments are provided, exit with an error and show a "usage" message to the user.
-2. Write a function taking a **folder path** and an **extension** as arguments and giving the list of matching files to the user
-<!-- 3. Imagine you are running jobs taking data from two folders, each with a dedicated extension. Use the two arguments of the script as the name of the two folders and **get the two lists of files**. 
-4. Since your work needs to read these files, **check that all files can be read**. If some files cannot be read, display their name to the user-->
-
-<!-- Créer un petit exercice raisonnable-->
+1. Write a script called `exercise_5.sh` expecting **2 arguments**. If not exactly two arguments are provided:
+    * Echo an error message
+    * Exit with a non-zero error code
+2. Write a function taking a **folder path** (e.g `/home/ucl/elic/xxxx`) and an **extension** (e.g `py`) as arguments
+3. Use the `ls` command to list the files in the given path having with the given extension. Write this list to a file called `files_found.txt`.
+4. Bonus : if there are no files, Exit with a non-zero error code 
 
 ---
 
@@ -929,8 +930,8 @@ Consider the script `test.sh` below :
 
 ```bash
 #!/bin/bash
-echo $var1
-echo $var2
+echo "var1 = ${var1}"
+echo "var2 = ${var2}"
 ```
 
 Then run this script :
@@ -940,6 +941,7 @@ var1=23
 export var2=12
 bash test.sh
 ```
+> By default, variables from the main interpreter are not available in scripts, unless you `export` them.
 
 ---
 
@@ -956,7 +958,7 @@ bash test.sh
 
 ### Syntax
 
-A command list embedded between parentheses runs as a subshell :
+A command list embedded **between parentheses** runs as a subshell :
 
 ```bash
 #!/bin/bash
@@ -976,8 +978,8 @@ bash -c "command1; command2; command3"
 
 ## Differences between **Sourcing** and **Executing** a script
 
-- source a script = execution in the current shell
-  > variables and functions are valid in the current shell after sourcing
+- source a script = execution **in the current shell**
+  > variables and functions are valid in the current shell after sourcing even if not `export`ed
 
 - execute a script = execution in a new shell (in a subshell of the current shell)
   > all new variables and functions created by the script will only live in the subshell
@@ -1041,7 +1043,7 @@ fi
 
 ### use `echo`
 
-"classical" but useful technique : insert `echo` throughout your code
+Classical but useful technique : insert `echo` throughout your code to check variable content
 
 ```bash
 #!/bin/bash