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 ${target_program_path_var}=\"\${candidate}\"
86    return
87
88  done
89
90}
91
92
93# Main
94
95  get_target_program_path target_program_path
96
97  # Compose program path var name (e.g. PYTHON_PGM_PATH).
98  pgm_path_var_name=${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.
101  eval export ${pgm_path_var_name}=${target_program_path}
102
103  if [ "${1}" == "--print_only" ] ; then
104    echo "${target_program_path}"
105  else
106    # Use exec in order to replace this process with the target process.
107    exec ${target_program_path} "${@}"
108  fi
109
110