Create string based on array values

Question

I am trying to create a tree structure like the tree command.

To keep track of the "heirarchy", I have an array like ("true" "true" "false") or ("true" "false" "false") or ("false" "true" "true") etc.

I want to build a string (that I will use to print the result on the terminal) which has Unicode based on the array.

For example ("true" "true" "false") would result in "│ │ "

("true" "false" "false") would result in in "│ "

and

("false" "true" "true") would result in " │ │ "

Where false is 2 spaces, true is unicode character \u2502 and a space. With the printf "%6s" | sed $'s/ /\u2502 /' command I can create spaces and replace one or all spaces (or 2 spaces) with unicode chars manually but I want to do it programmatically and also, the length on the array will change, doing manually can get very cumbersome.

Can someone guide? I am basically trying to add the lines in the places shown by red squiggles in the pic below

please update the question with the code you've tried and the (wrong) results generated by said code — markp-fuso
– markp-fuso, Commented Mar 17 at 14:48

Diego Torres Milano · Accepted Answer · 2025-03-17 23:41:11Z

1

Using sed:

sed 's/true/│ /g; s/false/  /g' <<< "${arr[*]}"

answered Mar 17 at 23:41

Diego Torres Milano

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Comments

JNevill · Accepted Answer · 2025-03-17 14:24:00Z

1

With a for loop:

for e in "${foo[@]}"; do 
    printf "%s" "$([[ $e == "true" ]] && echo '|' || echo ' ')"
done

answered Mar 17 at 14:24

JNevill

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Comments

markp-fuso · Accepted Answer · 2025-03-17 15:16:48Z

1

Define an associative array with the desired mappings, eg:

declare -A map=([true]=$'\u2502 ' [false]='  ')

A simple for loop can then be used to step through the main array, printing the associated mapping characters on each pass through the loop, eg:

for i in "${arr[@]}"
do
    printf "%s" "${map[$i]}"
done

NOTES: OP can follow this up with additional printf calls to finish populating a line of output; a simple printf "\n" or echo "" would suffice to terminate the line

Taking for a test drive (: added as prefix/suffix to show spacing):

$ arr=("true" "true" "false")
$ printf ":"; for i in "${arr[@]}"; do printf "%s" "${map[$i]}"; done; printf ":"
:│ │   :

$ arr=("true" "false" "false")
$ printf ":"; for i in "${arr[@]}"; do printf "%s" "${map[$i]}"; done; printf ":"
:│     :

$ arr=("false" "true" "true")
$ printf ":"; for i in "${arr[@]}"; do printf "%s" "${map[$i]}"; done; printf ":"
:  │ │ :

edited Mar 17 at 15:16

answered Mar 17 at 15:01

markp-fuso

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1 Comment

Toby Speight Mar 17 at 16:09

Your test-drive doesn't produce complete lines - final printf of each block needs to add \n or change to echo.

Toby Speight · Accepted Answer · 2025-03-17 16:07:45Z

1

Since we control the array, and only ever enter true or false, we can use those values as conditions:

arr=(true true false true)
for i in "${arr[@]}"
do if $i
   then printf '│ '
   else printf '  '
   fi
done
printf '- %s\n' ...name...

However, it might be better to store either │ or as each value in the array instead of true or false, allowing us to print the values directly without writing a loop:

arr=('│ ' '│ ' '  ' '│ ')
printf %s "${arr[@]}"
printf '├%s\n' ...name...

edited Mar 17 at 16:07

answered Mar 17 at 14:37

Toby Speight

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