I'm new to shell. I want to create a hashmap-style array.
I already took a look at this How to define hash tables in Bash?
It's not exactly what I want. This is what I expect:
myArray=(emma=paris, london, ny john=tokyo, LA)
#names are my keys and cities are my values
My actual code is like:
declare -A myArray=( ["$names"]="$cities" )
It doesn't work because each new city overwrites the last one.
danaso, did you quote the list of cities for each person, or did you quote each city individually? Things seem to work fine tfor me when I do the former. Here's a (slightly edited) transcript of my Bash session:
$ declare -A myArray=([emma]="paris london ny" [john]="tokyo LA")
Or, to create your associative array on the fly, as in your "actual code", from the regular arrays called names and cities, you would first create these arrays, like this:
$ declare -a names=(emma john) # Notice: small '-a' for inexed array.
$ declare -a cities=("paris london ny" "tokyo LA") # Notice: Quotes around whole lists of cities!
Then I would start with an empty myArray and build it up in a loop, like this:
$ declare myArray=()
for i in ${!names[@]}; do
name=${names[$i]}
city=${cities[$i]}
myArray+=([$name]=$city)
done
As an aside: Sometime in the future, you may want to populate myArray in this manner, but with different entries in your cities and names. If and when you do, it will be a good iea to set -o noglob before the for-loop. This disables pathname expansion by the shell and guards against trouble when you accidentally have a name or city called * in one of your arrays. You can re-enable it with set +o noglob after the for-loop.
Anyway, no matter which way you populate myArray, the new cities no longer overwrite the previous, as you can see:
$ echo ${myArray[emma]}
paris london ny
$ echo ${myArray[john]}
tokyo LA
And you can process the cities individually, such as in this for-loop:
$ for city in ${myArray[emma]}; do echo "hello, $city!"; done
hello, paris!
hello, london!
hello, ny!
How does that work for you?
PS: I'd like to thank Charles Duffy for the improvements to my code that he suggested in the comments.
Bash 4 supports associative arrays. But if using Bash 3 or lower, you can roll your own structure by using a regular array, then splitting each element on some separator such as =.
#!/bin/bash
array=(
emma="paris london ny"
john="tokyo LA"
)
for item in "${array[@]}"; do
key=$(cut -d "=" -f 1 <<< "$item")
value=$(cut -d "=" -f 2 <<< "$item")
echo "$key=$value"
done
Sample output:
emma=paris london ny
john=tokyo LA
The declare -A arrayName=( ["key"]="value" ) syntax should only be used when intending to replace the variable's contents outright, overwriting all preexisting values to leave only those described in the declaration.
When you want to add new values over time, use arrayName["$key"]="$value". Thus:
declare -A arrayName=( ) # Initialize an empty associative array
arrayName["key1"]=value1 # add key1
arrayName["key2"]=value2 # add key2
arrayName["key3"]=value3 # add key3
declare -p arrayName # print resulting array
...has the same result as:
# initialize with all three values already present
declare -A arrayName=( ["key1"]="value1" ["key2"]="value2" ["key3"]="value3" )
declare -p arrayName # print resulting array
...whereas the following discards all but the last:
declare -A arrayName=( ["key1"]="value1" ) # initialize with key1=value1
declare -A arrayName=( ["key2"]="value2" ) # discard and overwrite with key2=value2
declare -A arrayName=( ["key3"]="value3" ) # discard and overwrite with key3=value3
declare -p arrayName # output only has key3 and value3!
