Split output of command into an associative array in bash

Question

The output is

/     ext4
/boot ext2
tank  zfs

On each line the delimiter is a space. I need an associative array like:

"/" => "ext4", "/boot" => "ext2", "tank" => "zfs"

How is this done in bash?

Not at all, unfortunately. You can't have slashes in the keys of associative arrays in bash. What is it you're ultimately trying to achieve, so I can suggest workarounds? — Wintermute
– Wintermute, Commented May 30, 2015 at 1:23
@Wintermute, pardon? One certainly can; the only character not valid in a key's body is NUL. Did you actually test this claim? — Charles Duffy
– Charles Duffy, Commented May 30, 2015 at 2:24
@CharlesDuffy arr[/]=bar doesn't work for me with bash 4.3. Nor does anything else with / in it. bash: /: syntax error: operand expected (error token is "/") is the error. Quotes don't help. — Wintermute
– Wintermute, Commented May 30, 2015 at 10:23
@CharlesDuffy Oh, I was being stupid, my bad. Forgot the declare -A/didn't remember that it was necessary. I'll go stand in the corner now. — Wintermute
– Wintermute, Commented May 30, 2015 at 10:27

John1024 · Accepted Answer · 2015-05-30 07:03:58Z

19

If the command output is in file file, then:

$ declare -A arr=(); while read -r a b; do arr["$a"]="$b"; done <file

Or, you can read the data directly from a command cmd into an array as follows:

$ declare -A arr=(); while read -r a b; do arr["$a"]="$b"; done < <(cmd)

The construct <(...) is process substitution. It allows us to read from a command the same as if we were reading from a file. Note that the space between the two < is essential.

You can verify that the data was read correctly using declare -p:

$ declare -p arr
declare -A arr='([tank]="zfs" [/]="ext4" [/boot]="ext2" )'

edited May 30, 2015 at 7:03

answered May 30, 2015 at 1:29

John1024

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1 Comment

ShellFish Over a year ago

Wow this just blew my mind, I definitely need to read up on arrays.

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