docs(set-env-vars): add hints, fixx the test to block echo and fix solution

sh/tests/set-env-vars_test.sh

@@ -5,7 +5,16 @@ set -euo pipefail
 IFS='
 '
 
-submitted=$(bash student/set-env-vars.sh)
+FILENAME="student/set-env-vars.sh"
+
+if [ -s ${FILENAME} ]; then
+    if [[ $(cat $FILENAME | grep echo | wc -l) -ne 0 ]]; then
+        echo "echo is not allowed in this exercise!"
+        exit 1
+    fi
+fi
+
+submitted=$(bash $FILENAME)
 expected=$(bash solutions/set-env-vars.sh)
 
 diff <(echo "$submitted") <(echo "$expected")

sh/tests/solutions/set-env-vars.sh

@@ -3,5 +3,4 @@
 export MY_MESSAGE="Hello World"
 export MY_NUM=100
 export MY_PI=3.142
-export MY_ARR=(one, two, three, four, five)
-printenv
+printenv | grep "MY_"

subjects/devops/set-env-vars/README.md

@@ -2,7 +2,7 @@
 
 ### Instructions
 
-Create a script `set-env-vars.sh`, which will allow you to set the following variables as environment variables and and print them all:
+Create a script `set-env-vars.sh`, which will allow you to set the following variables as environment variables and and print only the ones you created:
 
 - `MY_MESSAGE` which contains the string `"Hello World"`.
 - `MY_NUM` which contains the number `100`.
@@ -28,28 +28,14 @@ LESSCLOSE=/usr/bin/lesspipe %s %s
 _=/usr/bin/printenv
 $ ./set-env-vars.sh
 MY_NUM=100
-SHELL=/bin/bash
-TERM=xterm
-USER=demouser
-LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:su=37;41:sg=30;43:ca:...
-MAIL=/var/mail/demouser
-PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
-PWD=/home/demouser
-LANG=en_US.UTF-8
 MY_PI=3.142
-SHLVL=1
-HOME=/home/demouser
-LOGNAME=demouser
 MY_MESSAGE=Hello World
-LESSOPEN=| /usr/bin/lesspipe %s
-LESSCLOSE=/usr/bin/lesspipe %s %s
-_=/usr/bin/printenv
 $
 ```
 
 ### Hints
 
-Setting values to environment variables
+Setting values to environment variables:
 
 In order to set a value to an existing environment variable, we use an assignment expression. For instance, to set the value of the "LANG" variable to "he_IL.UTF-8", we use the following command:
 
@@ -57,7 +43,7 @@ In order to set a value to an existing environment variable, we use an assignmen
 $ LANG=he_IL.UTF-8
 ```
 
-If we use an assignment expression for a variable that doesn't exist, the shell will create a shell variable, which is similar to an environment variable but does not influence the behaviour of other applications.
+If we use an assignment expression for a variable that doesn't exist, the shell will create a shell variable, which is similar to an environment variable but does not influence the behavior of other applications.
 
 A shell variable can be exported to become an environment variable with the export command. To create the "EDITOR" environment variable and assign the value "nano" to it, you can do:
 
@@ -66,5 +52,7 @@ $ EDITOR=nano
 $export EDITOR
 ```
 
+`echo` is not allowed in the exercise! Try to use the command `printenv` and filter with `grep` to get only the variables that you created.
+
 > You have to use Man or Google to know more about commands flags, in order to solve this exercise!
 > Google and Man will be your friends!