Creating a Bash associative array with glob output

Question

I want to create an associative array in Bash with file names derived from a glob as keys. Here is what I am doing:

declare -A file_hash
for file in *; do
  file_hash+=([$file]=1)
done

I am curious to see if there is a more straightforward way of doing the same thing, somewhat like how we initialize a normal array this way:

file_array=(*)

One of the ideas I got from another post on SO is:

file_array=(*)
declare -A file_hash=( $(echo ${file_array[@]} | sed 's/[^ ]*/[&]=&/g') )

Is that the best way?

Inspired from the echo method, this works OK in some tests, but requires eval : declare -A filehash; eval $(printf 'filehash+=(["%s"]=1);' *.txt) — George Vasiliou
– George Vasiliou, Commented Mar 6, 2017 at 0:44

chepner · Accepted Answer · 2017-03-05 21:01:24Z

2

Your loop is the correct way to do this. Anything else risks not properly handling filenames containing characters that the shell may treat specially, namely whitespace (and newlines in particular) and glob metacharacters like *, [], ?, etc.

file_array=(*) works as a shortcut for the longer, more explicit form

file_array=([0]=file1 [1]=file2 ...)

because the indices 0, 1, ... can be inferred from the sequence of files from the glob expansion. With an associative array, you cannot make any such assumption, and the keys and values must be given explicitly.

answered Mar 5, 2017 at 21:01

chepner

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