bin/gen_list.sh

#!/bin/bash

# This file contains list-manipulation functions.

# A list is defined here as a string of items separated by some delimiter.  The PATH variable is one such
# example.

if ! test "${default_delim+defined}" ; then
    readonly default_delim=" "
fi

# Performance note:  It is important for these functions to run quickly.  One way to increase their speed is
# to avoid copying function arguments to local variables and to instead use numbered arguments (e.g. ${1},
# {2}, etc.) to access the arguments from inside the functions.  In some trials, this doubled the speed of
# the functions.  The cost of this is that it makes the functions slightly more difficult to read.


function add_list_element() {
    # local list_element="${1}"
    # local list_name="${2}"
    # local delim="${3:-${default_delim}}"
    # local position="${4:-back}"

    # Add the list_element to the list named in list_name.

    # Description of argument(s):
    # list_element                    The list element to be added.
    # list_name                       The name of the list to be modified.
    # delim                           The delimiter used to separate list elements.
    # position                        Indicates the position in the list where the new element should be added
    #                                 ("front"/"back").

    if [ -z "${!2}" ] ; then
        # The list is blank. Simply assign it the list_element value and return.
        eval "${2}=\"${1}\""
        return
    fi

    if [ "${4:-back}" == "back" ] ; then
        # Append the list_element to the back of the list and return.
        eval "${2}=\"\${${2}}\${3-${default_delim}}\${1}\""
        return
    fi

    # Append the list_element to the front of the list and return.
    eval "${2}=\"\${1}\${3-${default_delim}}\${${2}}\""

}


function remove_list_element() {
    # local list_element="${1}"
    # local list_name="${2}"
    local delim="${3:-${default_delim}}"

    # Remove all occurrences of list_element from the list named in list_name.

    # Description of argument(s):
    # list_element                    The list element to be removed.
    # list_name                       The name of the list to be modified.
    # delim                           The delimiter used to separate list elements.

    local __rle_new_list__="${!2}"

    # Special case: The list contains one element which matches the specified list element:
    if [ "${1}" == "${__rle_new_list__}" ] ; then
        eval ${2}=\"\"
        return
    fi

    # Replace all occurrences of list_element that are bounded by the delimiter on both sides.
    __rle_new_list__="${__rle_new_list__//${delim}${1}${delim}/${delim}}"
    # Replace list_item if it occurs at the beginning of the string and is bounded on the right by the
    # delimiter.
    __rle_new_list__="${__rle_new_list__#${1}${delim}}"
    # Replace list_item if it occurs at the end of the string and is bounded on the left by the delimiter.
    __rle_new_list__="${__rle_new_list__%${delim}${1}}"

    # Set caller's variable to new value.
    eval ${2}=\"\${__rle_new_list__}\"

}


function cleanup_path_slashes() {
    local var_name="${1}" ; shift

    # For the variable named in var_name, replace all multiple-slashes with single slashes and strip any
    # trailing slash.

    # Description of argument(s):
    # var_name                        The name of the variable whose contents are to be changed.

    local cmd_buf

    cmd_buf="${var_name}=\$(echo \"\${${var_name}}\" | sed -re 's#[/]+#/#g' -e 's#/\$##g')"
    eval "${cmd_buf}"

}


function remove_path() {
    local dir_path="${1}" ; shift
    local path_var="${1:-PATH}" ; shift

    # Remove all occurrences of dir_path from the path variable named in path_var.

    # Note that this function will remove extraneous slashes from the elements of path_var.

    # Description of argument(s):
    # dir_path                        The directory to be removed from the path variable.
    # path_var                        The name of a variable containing directory paths separated by colons.

    cleanup_path_slashes dir_path || return 1
    cleanup_path_slashes ${path_var} || return 1
    remove_list_element "${dir_path}" "${path_var}" : || return 1

}