function that returns an array in bash [duplicate]

Question

I have a bash function that reads a csv file and I want that function to return an array. How do I do that?

I know that typically bash does not "return objects" but I wonder if there's a hack so that the following code:

data=$(readFromCSV $file)

returns an array from the custom function readFromCSV. And I mean $data being a true array so I could for instance run

echo {#data[@]}

and it would tell me how many items are in the array.

how would you tell the function to return the array?

thanks

Arrays are not values in bash. There is only array syntax that lets you treat a single name as a collection of separate variables. — chepner
– chepner, Commented Oct 4, 2021 at 13:34
stackoverflow.com/questions/10582763/… stackoverflow.com/questions/56456794/… stackoverflow.com/questions/14839199/… stackoverflow.com/questions/25291347/… — KamilCuk
– KamilCuk, Commented Oct 4, 2021 at 13:37

Bluz · Accepted Answer · 2021-10-04 15:06:32Z

-1

so basically this is how I proceeded to imitate "an array object" to be passed from a csv file.

First, create the function for the csv:

function readFromCSV() {
    file=$1
    arr_csv=() 
    while IFS= read -r line 
    do
        arr_csv+=("$line")
    done < $file

    echo ${arr_csv[*]} # this will output a string
}

then call the function:

list=$(readFromCSV $file)

then remap the string to an array:

arrayCSV=($list)

now arrayCSV is an array of the values frome the CSV file.

answered Oct 4, 2021 at 15:06

Bluz

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5 Comments

chepner Over a year ago

There's no point in defining the array inside the function. You'll get the exact same behavior if you just write each line to standard output: while IFS= read -r line; do echo "$line"; done < "$file".

Charles Duffy Over a year ago

Re: function funcName() {, see wiki.bash-hackers.org/scripting/obsolete -- this merges legacy ksh and POSIX syntax in a way that isn't compatible with either legacy ksh or POSIX.

Charles Duffy Over a year ago

...and as for the actual immediate question at hand, this is very broken code for no good reason. Bash 4.3 namerefs let you directly assign to a caller-named array from within a function. When you use echo ${arr_csv[*]}, you defeat the point of ever using an array in the first place, because you destroy the information about where element boundaries were originally stored.

Charles Duffy Over a year ago

To provide a concrete example, array=( "first element" "*" "third element" ) -- now when you string=$(echo ${array[*]}) and use newArray=( $string ), you get newArray[0]="first", newArray[1]="element", a list of filenames in the third element onward, etc; you've lost the information that first element was ever just one string, and that * was quoted.

Charles Duffy Over a year ago

@chepner, not the exact same behavior -- if one just echo'd a line at a time to stdout you could use readarray or mapfile to construct an array with correct boundaries on the outside, assuming no array elements contain literal newlines (not a 100% safe assumption, granted, being why NUL delimiters are better). What the OP is doing here is worse; their echo puts everything onto one line.

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