script bash Linux don't find error - linux

Question

I have to verify in a script bash that a folder exists. The problem is, it does but the script tells me that my file does not exist.
I don't find the error and I have searched on the internet and I do exactly the way it says to do( on Openclassroom, forum, ...).
here is my script:
#!/bin/bash
if [ $# -ne 1 ] && [ -d $1 ]; then
echo "Usage : $0 dir">/dev/stderr
exit 1
fi
backup="~/backup"
echo $backup , argument = $1
if [ ! -e ${backup} ]; then
echo "Le dossier backup n'existe pas">/dev/stderr
exit 1
fi
if [ ! -d $backup ]; then
echo "le document backup n'est pas un fichier">/dev/stderr
exit 1
fi
if [ -w $backup ]; then
echo "Le dossier backup n'est pas protégé en écriture">/dev/stderr
exit 1
fi
il qu$if [! chmod u=+w $backup ]; then
echo "une erreur c'est produite">/dev/stderr
exit 1
fi
And what it said in the shell + the proof that the file backup exist in the correct repertory:
guy#PC-DE-GUY:~/bash/Chap9$ ./backup.sh ~/seance06/
~/backup , argument = /home/guy/seance06/
Le dossier backup n'existe pas
guy#PC-DE-GUY:~/bash/Chap9$ ~/backup
bash: /home/guy/backup : est un dossier
guy#PC-DE-GUY:~/bash/Chap9$ cd ~/backup
guy#PC-DE-GUY:~/backup$

Answer 1

The issue is with the ~ character inside quotes, in backup="~/backup" (line 6). BASH processes it as a character, not as an alias to your home directory, so your code runs the checks on the string '~/backup', instead of '/home/guy/backup'.
To use ~ as an alias to your home directory, it should be outside quotes: backup=~/backup
If you want to hardcode your home directory, I suggest you use $HOME instead of ~. It's clearer to understand.
You can test what I tried to explain with the following code:
#!/bin/bash
# Save this file as test.sh
# run this script with ~ as an argument:
# ./test.sh ~
echo "Value for \$HOME: $HOME"
echo "Value for ~ inside quotes: ~"
echo "Value for ~ outside quotes:" ~
echo "Value for \$1: $1"
If you save the code above as test.sh and you run it as: ./test.sh ~, outputs will be:
Value for $HOME: /home/guy
Value for ~ inside quotes: ~
Value for ~ outside quotes: /home/guy
Value for $1: /home/guy