Bash

Compare integer in bash, unary operator expected error
```
if [[ $i -ge 2 ]]
```

Number tables

for i in {1..9}; do for j in $(seq 1 9); do echo -ne $i×$j=$((i*j))\\t;done; echo;done

Test of variable is a number in bash

re='^[0-9]+$'
if ! [[ $yournumber =~ $re ]] ; then
   echo "error: Not a number" >&2; exit 1
fi

Remove last character of variable
```
something="myname"
echo ${something%?}
```
Removing first character of variable
```
something="myname"
echo ${something#?}
```