1#!/bin/bash
2
3# This file contains list-manipulation functions.
4
5# A list is defined here as a string of items separated by some delimiter.  The PATH variable is one such
6# example.
7
8if ! test "${default_delim+defined}" ; then
9  readonly default_delim=" "
10fi
11
12# Performance note:  It is important for these functions to run quickly.  One way to increase their speed is
13# to avoid copying function arguments to local variables and to instead use numbered arguments (e.g. ${1},
14# {2}, etc.) to access the arguments from inside the functions.  In some trials, this doubled the speed of
15# the functions.  The cost of this is that it makes the functions slightly more difficult to read.
16
17
18function add_list_element {
19  # local list_element="${1}"
20  # local list_name="${2}"
21  # local delim="${3:-${default_delim}}"
22  # local position="${4:-back}"
23
24  # Add the list_element to the list named in list_name.
25
26  # Description of argument(s):
27  # list_element                    The list element to be added.
28  # list_name                       The name of the list to be modified.
29  # delim                           The delimiter used to separate list elements.
30  # position                        Indicates the position in the list where the new element should be added
31  #                                 ("front"/"back").
32
33  if [ -z "${!2}" ] ; then
34    # The list is blank. Simply assign it the list_element value and return.
35    eval "${2}=\"${1}\""
36    return
37  fi
38
39  if [ "${4:-back}" == "back" ] ; then
40    # Append the list_element to the back of the list and return.
41    eval "${2}=\"\${${2}}\${3-${default_delim}}\${1}\""
42    return
43  fi
44
45  # Append the list_element to the front of the list and return.
46  eval "${2}=\"\${1}\${3-${default_delim}}\${${2}}\""
47
48}
49
50
51function remove_list_element {
52  # local list_element="${1}"
53  # local list_name="${2}"
54  local delim="${3:-${default_delim}}"
55
56  # Remove all occurrences of list_element from the list named in list_name.
57
58  # Description of argument(s):
59  # list_element                    The list element to be removed.
60  # list_name                       The name of the list to be modified.
61  # delim                           The delimiter used to separate list elements.
62
63  local __rle_new_list__="${!2}"
64
65  # Special case: The list contains one element which matches the specified list element:
66  if [ "${1}" == "${__rle_new_list__}" ] ; then
67    eval ${2}=\"\"
68    return
69  fi
70
71  # Replace all occurrences of list_element that are bounded by the delimiter on both sides.
72  __rle_new_list__="${__rle_new_list__//${delim}${1}${delim}/${delim}}"
73  # Replace list_item if it occurs at the beginning of the string and is bounded on the right by the
74  # delimiter.
75  __rle_new_list__="${__rle_new_list__#${1}${delim}}"
76  # Replace list_item if it occurs at the end of the string and is bounded on the left by the delimiter.
77  __rle_new_list__="${__rle_new_list__%${delim}${1}}"
78
79  # Set caller's variable to new value.
80  eval ${2}=\"\${__rle_new_list__}\"
81
82}
83
84
85function cleanup_path_slashes {
86  local var_name="${1}" ; shift
87
88  # For the variable named in var_name, replace all multiple-slashes with single slashes and strip any
89  # trailing slash.
90
91  # Description of argument(s):
92  # var_name                        The name of the variable whose contents are to be changed.
93
94  local cmd_buf
95
96  cmd_buf="${var_name}=\$(echo \"\${${var_name}}\" | sed -re 's#[/]+#/#g' -e 's#/\$##g')"
97  eval "${cmd_buf}"
98
99}
100
101
102function remove_path {
103  local dir_path="${1}" ; shift
104  local path_var="${1:-PATH}" ; shift
105
106  # Remove all occurrences of dir_path from the path variable named in path_var.
107
108  # Note that this function will remove extraneous slashes from the elements of path_var.
109
110  # Description of argument(s):
111  # dir_path                        The directory to be removed from the path variable.
112  # path_var                        The name of a variable containing directory paths separated by colons.
113
114  cleanup_path_slashes dir_path || return 1
115  cleanup_path_slashes ${path_var} || return 1
116  remove_list_element "${dir_path}" "${path_var}" : || return 1
117
118}
119