Linux进阶bash笔记--Chapter 13: 关联数组

#!/usr/bin/env bash

declare -A assoc_array=([key_string]=value \
                        [one]="something" \
                        [two]="another thing" \
                        [ three ]='mind the blanks!' \
                        [ " four" ]='count the blanks of this key later!' \
                        [IMPORTANT]='SPACES DO ADD UP!!!' \
                        [1]='there are no integers!' \
                        [info]="to avoid history expansion " \
                        [info2]="quote exclamation mark with single quotes" \
                        )
echo # just a blank line
echo now here are the values of assoc_array:
echo ${assoc_array[@]}
echo not that useful,
echo # just a blank line
echo this is better:

declare -p assoc_array # -p == print

echo have a close look at the spaces above\!\!\!
echo # just a blank line

echo accessing the keys
echo the keys in assoc_array are ${!assoc_array[*]}
echo mind the use of indirection operator \!
echo # just a blank line

echo now we loop over the assoc_array line by line
echo note the \! indirection operator which works differently,
echo if used with assoc_array.
echo # just a blank line

for key in "${!assoc_array[@]}"; do # accessing keys using ! indirection!!!!
        printf "key: \"%s\"\nvalue: \"%s\"\n\n" "$key" "${assoc_array[$key]}"
done

echo have a close look at the spaces in entries with keys two, three and four above\!\!\!
echo # just a blank line
echo # just another blank line

echo there is a difference using integers as keys\!\!\!
i=1
echo declaring an integer var i=1
echo # just a blank line
echo Within an integer_array bash recognizes artithmetic context.
echo Within an assoc_array bash DOES NOT recognize artithmetic context.
echo # just a blank line
echo this works: \${assoc_array[\$i]}: ${assoc_array[$i]}
echo this NOT!!: \${assoc_array[i]}: ${assoc_array[i]}
echo # just a blank line
echo # just a blank line
echo an \${assoc_array[i]} has a string context within braces in contrast to an integer_array
declare -i integer_array=( one two three )
echo "doing a: declare -i integer_array=( one two three )"
echo # just a blank line

echo both forms do work: \${integer_array[i]} : ${integer_array[i]}
echo and this too: \${integer_array[\$i]} : ${integer_array[$i]}