Script returns full binary name

Makefile

@@ -96,28 +96,16 @@ build-deps-ubuntu:
 docs: docs-deps docs-build
 
 docs-build: .PHONY
-	@if ! SUFFIX=$$(tools/get-best-python-for-docs-build.sh); then \
-		echo "ERROR: could not find a recent version of Python. mkdocs needs >= 3.8"; \
-		exit 1; \
-	fi; \
-	echo "python$$SUFFIX $$(which mkdocs) build"; \
-	"python$$SUFFIX" $$(which mkdocs) build
+	PY=$$(tools/get-python-bin.sh python) && MKDOCS=$$(which mkdocs) && \
+	$$PY $$MKDOCS build
 
 docs-deps: .PHONY
-	@if ! SUFFIX=$$(tools/get-best-python-for-docs-build.sh); then \
-		echo "ERROR: could not find a recent version of Python. mkdocs needs >= 3.8"; \
-		exit 1; \
-	fi; \
-	echo "pip$$SUFFIX install -r requirements.txt"; \
-	"pip$$SUFFIX" install -r requirements.txt
+	PIP=$$(tools/get-python-bin.sh pip) && \
+	$$PIP install -r requirements.txt
 
 docs-deps-update: .PHONY
-	@if ! SUFFIX=$$(tools/get-best-python-for-docs-build.sh); then \
-		echo "ERROR: could not find a recent version of Python. mkdocs needs >= 3.8"; \
-		exit 1; \
-	fi; \
-	echo "pip$$SUFFIX install -r requirements.txt --upgrade"; \
-	"pip$$SUFFIX" install -r requirements.txt --upgrade
+	PIP=$$(tools/get-python-bin.sh pip) && \
+	$$PIP install -r requirements.txt --upgrade
 
 # Web app
 

tools/get-python-bin.sh

@@ -1,20 +1,31 @@
 #!/usr/bin/env bash
 
-# This script prints the version suffix of the most suitable version of Python
-# for building docs that's installed in this system.
+# Synopsis:
+# - get-python-bin.sh python
+# - get-python-bin.sh pip
 #
-# Caller can safely append this suffix to `python` or `pip` and expect the
-# binary to exist.
+# This script selects the most suitable `python` / `pip` binary available
+# for building docs that's installed in this system.
 #
 # If no usable version of Python is available, this script will exit with a
 # non-zero code.
 
 set -e
 
+case "$1" in
+    "python" | "pip")
+        BIN_PREFIX="$1"
+        ;;
+    *)
+        echo "Incorrect usage" >&2
+        exit 1
+        ;;
+esac
+
 # if `python3` is >= 3.8 and `pip3` is available, use that
 if echo -e "import sys\nif sys.version_info < (3,8):\n exit(1)" | python3 && \
 which pip3 1>/dev/null 2>&1; then
-    echo "3"
+    echo "${BIN_PREFIX}3"
     exit 0
 fi
 
@@ -24,10 +35,11 @@ for SUFFIX in ${CANDIDATE_SUFFIXES[@]}; do
     # if both `python3.N` and `pip3.N` are available, use that
     if which "python$SUFFIX" 1>/dev/null 2>&1 && \
     which "pip$SUFFIX" 1>/dev/null 2>&1; then
-        echo "$SUFFIX"
+        echo "${BIN_PREFIX}${SUFFIX}"
         exit 0
     fi
 done
 
 # none found
-exit 1
+echo "No suitable version of Python found" >&2
+exit 2