libhash

Set of functions for working with an associative array type data structure. Values can be stored and retrieved using strings as the index into the data structure instead of numbers. The hash data structure provided in this file allows you to store values into fields of a table. The 'hash_put' function takes the name of the table, a field name in the table, and the value to be stored in the table. The 'hash_get' function retrieves a value from the table given the table and field name.

To store a value into a field of a table, use hash_put:
hash_put "myTable" "aField" "theValue"
The value stored in the table can be retrieved with hash_get:
hash_get "myTable" "aField"
In this example, the hash_get function would echo "theValue".
hash_get_ref can also be used here and has the benefit of being forkless.

IMPLEMENTATION NOTE

Bash does not provide direct support for hash tables. These functions are implemented by first building a variable using the table name and field name, then using the eval function to store (retrieve) value into (from) the variable.
The idea for the hash data structure in bash was inspired by a short example by Phil Howard which shows the use of hashes in bash. Phil Howard's original example can be found here: http://www.codebits.com/bit.cfm?BitID=92

Copyright

function hash_build_variable_name()

Parameters:

$1: table name
$2: field name
$3: returning variable

Type

Private

Description

Given a table and field name, bulds the name of the variable into which a value will be stored. Also changes '+', '-', and '.' in the table name into text since bash doesn't like variable names with those characters.

function hash_unbuild_field_name()

Parameters:

$1: field name
$2: table name
$3: returning variable

Type

Private

Description

most likely reverses hash_build_field_name

function hash_put()

Parameters:

$1: table name
$2: field name
$3: value

Description

Saves the value in the specified table/field.

function hash_get()

Parameters:

$1: table name
$2: field name

Stdout

Value stored in table/field

Description

Echos the value stored in the table/field. If no value was previously stored in the table/field, this function echos an empty string.

function hash_get_ref()

Parameters:

$1: table name
$2: field name
$3: upvar name

Stdout

none

Description

Returns the value stored in the table/field through the upvar variable name. If no value was previously stored in the table/field, then an empty string is returned.

function hash_append()

Parameters:

$1: table name
$2: field name
$3: value

Description

Appends the value to the specified table/field.

function hash_export()

Parameters:

$1: table name

Description

'export' all the values in the table. This is useful for getting hash table data from cast's pass_one/two into pass_three/pass_four which are run through make. Essentially exporting lets us pass the variables through make.