From afebcbabc1fce1871834da0d86e0cdb959c13ace Mon Sep 17 00:00:00 2001
From: Mo8it <mo8it@proton.me>
Date: Mon, 26 Sep 2022 20:56:41 +0200
Subject: [PATCH] Add if block

---
 src/day_2/shell_scripting.md | 84 +++++++++++++++++++++++++++++++++---
 1 file changed, 78 insertions(+), 6 deletions(-)

diff --git a/src/day_2/shell_scripting.md b/src/day_2/shell_scripting.md
index 370cfd6..b8478eb 100644
--- a/src/day_2/shell_scripting.md
+++ b/src/day_2/shell_scripting.md
@@ -4,9 +4,9 @@ Task automation requires multiple instructions that have to run on demand. To co
 
 Since `bash` is the default shell on most Linux distributions, we learn bash scripting.
 
-## First script
+## First bash script
 
-Lets write our first Bash script (also for some more demonstration of the two output forms from the last chapter):
+Lets write our first Bash script:
 
 ```bash
 #!/usr/bin/bash
@@ -73,7 +73,7 @@ This means that we can now write this script:
 print("Hello world!")
 ```
 
-Lets save this tiny Python script as `hello_world.py`, make it executable (will be explained later) and then run it:
+Lets save this tiny Python script as `hello_world.py`, make it executable with `chmod` (will be explained later) and then run it:
 
 ```console
 $ chmod u+x hello_world.py
@@ -204,16 +204,88 @@ In a script, you can ask for user input. To do so, you can use the command `read
 
 In our first bash script, we use `read` to take the answer of the user. The input is then saved in the variable `ANSWER`. You can choose a different name for this variable. After the line with `read`, you can use the variable storing the input as a normal variable.
 
-<!-- TODO: if -->
+## Conditions
 
-<!-- TODO: test -->
+### `if` block
 
-<!-- TODO: if [ ! -f ] -->
+Our first bash script checks if the user input which is stored in the variable `ANSWER` equals the variable `RIGHT_ANSWER` which stores the value `1`.
+
+To check for a condition in Bash, we use the following syntax:
+
+```bash
+if [ CONDITION ]
+then
+    (...)
+fi
+```
+
+Here, `(...)` stands for the commands that we want to run if the condition is true.
+
+In our first bash script, we check for equality of two variables with a double equal sign `==`.
+
+`fi` is not a typo! It is just `if` reversed to indicate the end of the `if` block. Although the syntax is not the best, you have to sadly accept it. Bash does not have the best syntax...
+
+Speaking about syntax: You have to take spaces seriously with conditions.
+
+For example, if we define the variable `VAR=1`, the following snippets **do not work**:
+
+1. No space after `[`
+   ```bash
+   if [$VAR == 1 ]
+   then
+       echo "VAR has the value 1"
+   fi
+   ```
+
+1. No space before `]`
+   ```bash
+   if [ $VAR == 1]
+   then
+       echo "VAR has the value 1"
+   fi
+   ```
+1. No space before `==` but a space after `==`
+   ```bash
+   if [ $VAR== 1 ]
+   then
+       echo "VAR has the value 1"
+   fi
+   ```
+1. No space after `==` but a space before `==`
+   ```bash
+   if [ $VAR ==1 ]
+   then
+       echo "VAR has the value 1"
+   fi
+   ```
+
+But the following snippets **work**:
+
+1. Space after `[`, before `]`, before `==` and after `==`
+   ```bash
+   if [ $VAR == 1 ]
+   then
+       echo "VAR has the value 1"
+   fi
+   ```
+1. Space after `[` and before `]`. No space before `==` and after `==`
+   ```bash
+   if [ $VAR==1 ]
+   then
+       echo "VAR has the value 1"
+   fi
+   ```
+
+### `else` block
 
 <!-- TODO: else -->
 
 <!-- TODO: else if -->
 
+<!-- TODO: test -->
+
+<!-- TODO: if [ ! -f ] -->
+
 <!-- TODO: case -->
 
 <!-- TODO: for -->