Make launcher find python binary

bin/dotbot

@@ -1,4 +1,20 @@
-#!/usr/bin/env python
+#!/usr/bin/env sh
+
+# This is a valid shell script and also a valid Python script. When this file
+# is executed as a shell script, it finds a python binary and executes this
+# file as a Python script, passing along all of the command line arguments.
+# When this file is executed as a Python script, it loads and runs Dotbot. This
+# is useful because we don't know the name of the python binary.
+
+''':' # begin python string; this line is interpreted by the shell as `:`
+which python3 >/dev/null 2>&1 && exec python3 "$0" "$@"
+which python  >/dev/null 2>&1 && exec python  "$0" "$@"
+which python2 >/dev/null 2>&1 && exec python2 "$0" "$@"
+>&2 echo "error: cannot find python"
+return 1
+'''
+
+# python code
 
 import sys, os
 

test/tests/find-python-executable.bash

@@ -0,0 +1,58 @@
+test_description='can find python executable with different names'
+. '../test-lib.bash'
+
+# the test machine needs to have a binary named `python`
+test_expect_success 'setup' '
+mkdir ~/tmp_bin &&
+(
+    IFS=:
+    for p in $PATH; do
+        find $p -maxdepth 1 -mindepth 1 -exec sh -c \
+            '"'"'ln -sf {} $HOME/tmp_bin/$(basename {})'"'"' \;
+    done
+) &&
+rm -f ~/tmp_bin/python &&
+rm -f ~/tmp_bin/python2 &&
+rm -f ~/tmp_bin/python3
+'
+
+test_expect_failure 'run' '
+PATH="$HOME/tmp_bin" run_dotbot <<EOF
+[]
+EOF
+'
+
+test_expect_success 'setup 2' '
+touch ~/tmp_bin/python &&
+chmod +x ~/tmp_bin/python &&
+cat >> ~/tmp_bin/python <<EOF
+#!$HOME/tmp_bin/sh
+exec $(which python)
+EOF
+'
+
+test_expect_success 'run 2' '
+PATH="$HOME/tmp_bin" run_dotbot <<EOF
+[]
+EOF
+'
+
+test_expect_success 'setup 3' '
+mv ~/tmp_bin/python ~/tmp_bin/python2
+'
+
+test_expect_success 'run 3' '
+PATH="$HOME/tmp_bin" run_dotbot <<EOF
+[]
+EOF
+'
+
+test_expect_success 'setup 4' '
+mv ~/tmp_bin/python2 ~/tmp_bin/python3
+'
+
+test_expect_success 'run 4' '
+PATH="$HOME/tmp_bin" run_dotbot <<EOF
+[]
+EOF
+'