1) Script to output the number of days passed since the beginning of the year:

#!/bin/bash
days=$(date +"%j")
echo "Number of days passed since the beginning of the year: $days"

Save this script as days_passed.sh and run it using ./days_passed.sh.

2) Script to set, output, erase environmental variable or exit:

#!/bin/bash
echo "Enter a value:"
read value
case $value in
1)
echo "Enter a value to set the environmental variable:"
read var_value
export ENV_VAR="$var_value"
echo "Environmental variable set"
;;
2)
echo "Environmental variable value: $ENV_VAR"
;;
3)
unset ENV_VAR
echo "Environmental variable erased"
;;
4)
exit 0
;;
*)
echo "Error: Invalid option entered"
exit 1
;;
esac

Save this script as env_var_operations.sh and run it using ./env_var_operations.sh.