Write me POSIX-shellscript to convert Celsius to Kelvin.
The following POSIX shell script can be used to convert Celsius to Kelvin. It uses the `bc` program to perform the actual computation.

```sh
#!/bin/sh

# Check if an argument has been passed to the script
if [ $# -eq 0 ]; then
  echo Usage: $0 <celsius_temperature>
  exit 1
fi

# Read the celsius value from the first argument given to the script
temp_c=$1

# Convert Celsius to Kelvin utilizing the basic calculator
temp_k=$(echo $temp_c + 273.15 | bc)

# Print the result to stdout
echo $temp_c °C = $temp_k K
```

If the script is saved as a file named `convert.sh`, 23°C could be converted to Kelvin by typing `sh convert.sh 23`