require that EESSI version to use is specified in eessi shell via --eessi-version option

README.md

@@ -50,7 +50,11 @@ To see which commands this would evaluate, just run `eessi init`.
 
 Create subshell in which EESSI is available and initialised
 
-*(to be implemented)*
+```shell
+eessi shell --eessi-version 2025.06
+```
+
+You *must* specify the EESSI version to use, there is no default value for this.
 
 ## Design goals
 

src/eessi/cli/shell.py

@@ -7,20 +7,35 @@
 import tempfile
 import typer
 from rich import print as rich_print
+from typing import Annotated
 
 app = typer.Typer()
 
 
+def report_error(msg, exit_code: int = 1):
+    """
+    Report error and exit with specified non-zero exit code
+    """
+    rich_print(f"[bold red]{msg}", file=sys.stderr)
+    if exit_code <= 0:
+        raise ValueError(f"Exit code should be positive non-zero integer, got {exit_code}")
+    sys.exit(exit_code)
+
+
 @app.command()
-def shell():
+def shell(
+    eessi_version: Annotated[str, typer.Option(help="EESSI version")] = '',
+):
     """
     Create subshell in which EESSI is available and initialised
     """
+    if not eessi_version:
+        report_error("EESSI version to use is not specified, which is required!")
+
     init_file = tempfile.mkstemp()[1]
     with open(init_file, 'w') as fp:
-        fp.write("set -e; source /cvmfs/software.eessi.io/versions/2023.06/init/bash")
+        fp.write(f"set -e; source /cvmfs/software.eessi.io/versions/{eessi_version}/init/bash")
 
     res = subprocess.run(['/bin/bash', '--init-file', init_file])
     if res.returncode != 0:
-        rich_print("[bold red]ERROR: Non-zero exit code detected for interactive shell!", file=sys.stderr)
-        sys.exit(res.returncode)
+        report_error("ERROR: Non-zero exit code detected for interactive shell!", exit_code=res.returncode)