1#!/bin/bash
2
3# This script is a wrapper for programs that may have alternate versions (e.g. python2, python3).  This
4# wrapper allows the user to influence the selection of the program version by setting the <program
5# name>_VERSION (e.g. PYTHON_VERSION, ROBOT_VERSION, etc.) environment variable.
6
7# Users would be expected to create a link with the base name of the program that points to this file.
8
9# Example:
10# cd openbmc-test-automation/bin
11# ln -s select_version python
12
13# The PATH variable should contain the expanded path to openbmc-test-automation/bin.
14
15# If <program name>_VERSION is blank or not set, then the program version will be whatever the system
16# default program version is.  If <program name>_VERSION is set to a value, then that value will be appended
17# to the name of the program (e.g. if PYTHON_VERSION = "3", then python3 will be used.).  If <program
18# name>_VERSION is set to some value that does not correspond to a valid program version for the given
19# system, this program will fail.
20
21
22# Make sure program_name is set.
23program_name="${0##*/}"
24program_uppercase_name=${program_name^^}
25
26
27function get_target_program_path() {
28    local target_program_path_var="${1:-target_program_path}" ; shift
29
30    # Get the full path to the "real" program and assign it to the variable named in target_program_path_var.
31
32    # Description of argument(s):
33    # target_program_path_var         The name of the variable to receive the result.
34
35    # Example result:
36
37    # /usr/bin/python3
38
39    local version_var_name
40    local alternate_program_name
41    local base_program_path
42    local base_program_name
43    local candidate
44    local candidates
45    local base_file_path
46
47    # The typical use of this program would be to create a link to it like this:
48    # ln -s select_version python
49    # That being the case, get the name of this actual program (rather than the name of the link to it).
50    base_program_path=$(readlink -f "${0}")
51    base_program_name=${base_program_path##*/}
52
53    if [ "${program_name}" == "${base_program_name}" ] ; then
54        {
55            echo -n "**ERROR** ${base_program_name} should never be called directly."
56            echo "  Only links to ${base_program_name} should be called."
57        } >&2
58        exit 1
59    fi
60
61    # Compose the version_var_name value (e.g. PYTHON_VERSION).
62    version_var_name=${program_uppercase_name}_VERSION
63    # Compose the alternate_program_name (e.g. python3).
64    alternate_program_name=${program_name}${!version_var_name}
65
66    # Now use the "type" built-in to search the PATH variable for a list of target program candidates.
67    candidates=$(type -ap ${alternate_program_name})
68
69    # Example candidates:
70    # /home/robot/openbmc-test-automation/bin/python
71    # /usr/bin/python
72
73    # In this example, the first candidate is actually a link to
74    # /home/robot/openbmc-test-automation/bin/select_version.  As such it will be rejected.
75
76    for candidate in ${candidates}
77    do
78        if [ -L "${candidate}" ] ; then
79            # The candidate is a link so we need to see if it's a link to this program file.
80            base_file_path=$(readlink "${candidate}")
81            [ "${base_file_path}" == "${base_program_name}" ] && continue
82        fi
83
84        # The candidate is NOT a link so it qualifies as the desired target program path.
85        eval ${target_program_path_var}=\"\${candidate}\"
86        return
87
88    done
89
90}
91
92
93# Main
94
95get_target_program_path target_program_path
96
97# Compose program path var name (e.g. PYTHON_PGM_PATH).
98pgm_path_var_name=${program_uppercase_name}_PGM_PATH
99# Set and export pgm_path_var_name (e.g. PYTHON_PGM_PATH=/usr/bin/python3).  This value can be used by
100# child programs for debug.
101eval export ${pgm_path_var_name}=${target_program_path}
102
103if [ "${1}" == "--print_only" ] ; then
104    echo "${target_program_path}"
105else
106    # Use exec in order to replace this process with the target process.
107    exec ${target_program_path} "${@}"
108fi
109
110