Update file Bash.md

Bash.md

@@ -76,10 +76,6 @@ echo $STRING
 
 ---
 
-![h:600](assets/scripting.png)
-
----
-
 # Bash environment
 
 In a Bash shell many things constitute your environment
@@ -184,6 +180,12 @@ Your first bash script:
 4. make the file executable
 5. run it !
 
+<!-- 
+
+Durée max: 10-15 min
+
+-->
+
 ---
 
 # Variables and data types in Bash
@@ -228,22 +230,23 @@ myvar=$( ls )
 
 ## Variable naming conventions
 
-* Variable names **should start** with a letter or an underscore
+- Variable names **should start** with a letter or an underscore
 
-* Variable names can contain letters, numbers, and underscores
+- Variable names can contain letters, numbers, and underscores
 
-* Variable names are **case-sensitive**
+- Variable names are **case-sensitive**
 
-* Variable names **should not** contain spaces or **special characters**
+- Variable names **should not** contain spaces or **special characters**
 
-* Use descriptive names that reflect the purpose of the variable
+- Use descriptive names that reflect the purpose of the variable
 
-* 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 to avoid conflicts with builtins
+- **Never** name your private variables using only **UPPERCASE** characters to avoid conflicts with builtins
 
 ---
 
+<!--
 ## String manipulation
 
 Consider `string=abcABC123ABCabc`
@@ -255,20 +258,21 @@ Consider `string=abcABC123ABCabc`
   * `${string:(-4)}` or `${string: -4}` is `Cabc` 
 
 ---
+-->
 
 ## String manipulation
 
 Consider `filename=/var/log/messages.tar.gz`
 
-* substring removal from left :
-  * `${filename##/var}` is `/log/messages.tar.gz`
-* substring removal from right :
-  * `${filename%%.gz}` is `/var/log/messages.tar`
+- substring removal from left :
+  - `${filename##/var}` is `/log/messages.tar.gz`
+- substring removal from right :
+  - `${filename%%.gz}` is `/var/log/messages.tar`
 
 You can use `*` to match all characters:
 
-* `${filename%%.*}` is `/var/log/messages`
-* `$(filename##*/)` is `messages.tar.gz`
+- `${filename%%.*}` is `/var/log/messages`
+- `$(filename##*/)` is `messages.tar.gz`
 
 ---
 
@@ -340,19 +344,19 @@ echo $b # 16
 # Conditional statements
 
 Use:
-* `if condition; then` to start conditional block
-* `else` to start alternative block
-* `elif` to start alternative condition block
-* `fi` to close conditional block
+- `if condition; then` to start conditional block
+- `else` to start alternative block
+- `elif` to start alternative condition block
+- `fi` to close conditional block
 
 The following operaors can be used beween conditions:
 
-* `||` means **OR**
-* `&&` mean **AND** 
+- `||` means **OR**
+- `&&` mean **AND** 
 
 ---
 
-# Conditional exemple
+# Conditional example
 
 ```bash 
 #!/bin/bash
@@ -368,6 +372,12 @@ else
 fi
 ```
 
+<!--
+
+NOTE: réfléchir à la meilleure syntaxe à utiliser ( les ((, les [ ], les [[]] )
+
+-->
+
 ---
 
 |  Operator    |     Description   |
@@ -449,12 +459,12 @@ 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 than 100 and 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
-   > read NUMBER1
-   > read NUMBER2
+   > read number1
+   > read number2
    >```
 
 3. Check if the numbers are smaller than 100
@@ -536,16 +546,13 @@ Useful for automating repetitive tasks
 
 Basic loop structures in Bash scripting :
 
-* `while` : perform a set of commands while a test is true
-* `until` : perform a set of commands until a test is true
-* `for` : perform a set of commands for each item in a list
-
-* controlling loops
+- `while` : perform a set of commands while a test is true
+- `for` : perform a set of commands for each item in a list
 
-  * `break` : exit the currently running loop
-  * `continue` : stop this iteration of the loop and begin the next iteration
+- controlling loops
 
-* last loop mechanism : `select` allows you to create a simple menu system
+  - `break` : exit the currently running loop
+  - `continue` : stop this iteration of the loop and begin the next iteration
 
 ---
 
@@ -575,7 +582,7 @@ for word in $words
 ```
 ```bash
 # range with steps for loop
-for value in {10..0..2}
+for value in {10..0..-2}
 ```
 ```bash
 # set of files
@@ -620,6 +627,13 @@ done
 5. Register the end time in `tend`
 6. Display the total run time and the total number of letters.
 
+
+<!--
+
+PY: modifier pour avoir un exemple de 10 mots directement dans le slide
+
+-->
+
 ---
 
 # Arguments - Positional Parameters
@@ -697,6 +711,12 @@ Shells use 3 standard I/O streams
 
 Shell has several **meta-characters** and **control operators** 
 
+<!--
+
+Jerome: refaire ces 3 slides
+
+-->
+
 ---
 
 # Control operators
@@ -708,7 +728,8 @@ Shell has several **meta-characters** and **control operators**
 | `\|\|` | Execute next command only if command fails |
 | `&` | Don't wait for result of command before starting next command |
 | `\|` | Use output of command as input for the next command |
-| `> file_desc` | Send stdandard output of command to file descriptor |
+| `> file_desc` | Send standard output of command to file descriptor |
+| `>> file_desc` | Same but in append mode |
 | `< file_desc` | Use content of file descriptor as input |
 
 ---
@@ -751,6 +772,11 @@ done < "$input"
 > by default `read` removes all leading and trailing whitespace characters such as spaces and tabs
 
 <!-- 
+
+!!!!!!!!!!!!!!!!!!!!!
+REMPLACER cet exemple : a propos de l'entrée standard
+
+
 `while IFS= read -r line`
 
 The internal field separator (`IFS`) is set to the empty string to preserve whitespace issues
@@ -764,10 +790,10 @@ The `-r` option is used not to allow backslashes to escape any characters
 
 Linux command returns a status when it terminates normally or abnormally
 
-* every Linux command has an exit status
-* the exit status is an integer number
-* a command which exits with a **0** status has **succeeded**
-* a **non-zero** (1-255) exit status indicates **failure**
+- every Linux command has an exit status
+- the exit status is an integer number
+- a command which exits with a **0** status has **succeeded**
+- a **non-zero** (1-255) exit status indicates **failure**
 
 How do I display the exit status of shell command ?
 
@@ -797,10 +823,12 @@ command || echo "failed"
 command && echo "success" || echo "failed"
 ```
 
+<!--
 ```bash
 _files="$@"
 [[ "$_files" == "" ]] && { echo "Usage: $0 file1.png file2.png"; exit 1; }
 ```
+-->
 <!-- Attention utilisatin du [[ ]] pas encore expliqué ? -->
 
 ---
@@ -816,10 +844,10 @@ _files="$@"
 
 # Functions
 
-* "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 code
+- "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 code
 
 ```bash
 #!/bin/bash
@@ -857,7 +885,7 @@ echo $var
 ```
 
 ---
-
+<!--
 ## Return Values 
 
 Bash functions don’t allow you to return a value when called
@@ -876,22 +904,11 @@ echo $?
 ```
 
 ---
-
-Return an arbitrary value (different from a return code) from a function : 
-* Assign the result of the function
-
-```bash
-my_function () {
-  func_result="some result"
-}
-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`
+# Return an arbitrary value from a function 
+
+Assign the result of the function
 
 ```bash
 my_function () {
@@ -922,15 +939,24 @@ print_something Mars
 
 # Hands-on exercise
 
-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
+1. Write a script called `exercise_5.sh` expecting **2 arguments**. 
 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 
 
 ---
 
+# Subshells
+
+- A subshell is a "child shell" spawned by the main shell ("parent shell")
+- A subshell is a **separate** instance of the command process, run as a new process
+- **Unlike calling a shell script** (slide before), subshells inherit the **same** variables as the original process
+- A subshell allows you to execute commands within a separate shell environment = *Subshell Sandboxing*
+  > useful to set temporary variables or change directories without affecting the parent shell's environment 
+- Subshells can be used for **parallel processing** 
+
+---
+
 # Shell vs Environment Variables
 
 Consider the script `test.sh` below :
@@ -950,16 +976,7 @@ bash test.sh
 ```
 > By default, variables from the main interpreter are not available in scripts, unless you `export` them.
 
----
-
-# Subshells
-
-* A subshell is a "child shell" spawned by the main shell ("parent shell")
-* A subshell is a **separate** instance of the command process, run as a new process
-* **Unlike calling a shell script** (slide before), subshells inherit the **same** variables as the original process
-* A subshell allows you to execute commands within a separate shell environment = *Subshell Sandboxing*
-  > useful to set temporary variables or change directories without affecting the parent shell's environment 
-* Subshells can be used for **parallel processing** 
+<!--
 
 ---
 
@@ -981,15 +998,14 @@ bash -c "command1; command2; command3"
 
 > Reminder : variables in a subshell are **not** visible outside the block of code in the subshell
 
+-->
+
 ---
 
 ## 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 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
 
 Source a script using `source` or `.`
 
@@ -1006,27 +1022,33 @@ source myScript.sh
 
 ```bash
 #!/bin/bash
-COUNTRY="Belgium"
+country="Belgium"
 greeting() {
     echo "You're in $1"
 }
-greeting $COUNTRY
+greeting $country
 ```
 
 ```bash
-COUNTRY="France"
-./myScript.sh # or bash or exec
-echo $COUNTRY
-greeting $COUNTRY # !!
+country="France"
+./myScript.sh # or bash
+echo $country
+greeting $country # !!
 ```
 
 ```bash
-COUNTRY="France"
+country="France"
 source myScript.sh
-echo $COUNTRY
-greeting $COUNTRY
+echo $country
+greeting $country
 ```
 
+<!--
+
+!!!!!!!!!!!!!!!! A REDISCUTER
+
+-->
+
 ---
 
 # Debug