Removing duplicates on a variable without sorting

Question

I have a variable that contains the following space separated entries.

variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"

How do I remove the duplicates without sorting?

#Something like this.
new_variable="apple lemon papaya avocado grapes mango banana"

I have found somewhere a script that accomplish removing the duplicates of a variable, but does sort the contents.

#Not something like this.
new_variable=$(echo "$variable"|tr " " "\n"|sort|uniq|tr "\n" " ")
echo $new_variable
apple avocado banana grapes lemon mango papaya

Answer 1

new_variable=$( awk 'BEGIN{RS=ORS=" "}!a[$0]++' <<<$variable );

Here's how it works:

RS (Input Record Separator) is set to a white space so that it treats each fruit in $variable as a record instead of a field. The non-sorting unique magic happens with !a[$0]++. Since awk supports associative arrays, it uses the current record ($0) as the key to the array a[]. If that key has not been seen before, a[$0] evaluates to '0' (awk's default value for unset indices) which is then negated to return TRUE. I then exploit the fact that awk will default to 'print $0' if an expression returns TRUE and no '{ commands }' are given. Finally, a[$0] is then incremented such that this key can no longer return TRUE and thus repeat values are never printed. ORS (Output Record Separator) is set to a space as well to mimic the input format.

A less terse version of this command which produces the same output would be the following:

awk 'BEGIN{RS=ORS=" "}{ if (a[$0] == 0){ a[$0] += 1; print $0}}'

Gotta love awk =)

EDIT

If you needed to do this in pure Bash 2.1+, I would suggest this:

#!/bin/bash    

variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"
temp="$variable"

new_variable="${temp%% *}"

while [[ "$temp" != ${new_variable##* } ]]; do
   temp=${temp//${temp%% *} /}
   new_variable="$new_variable ${temp%% *}"
done

echo $new_variable;

Answer 2

This pipeline version works by preserving the original order:

variable=$(echo "$variable" | tr ' ' '\n' | nl | sort -u -k2 | sort -n | cut -f2-)

Answer 3

Pure Bash:

variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"

declare new_value=''

for item in $variable; do
  if [[ ! $new_value =~ $item ]] ; then   # first time?
    new_value="$new_value $item"
  fi
done
new_value=${new_value:1}                  # remove leading blank

Answer 4

In pure, portable sh:

words="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"
seen=
for word in $words; do
  case $seen in
    $word\ * | *\ $word | *\ $word\ * | $word) 
      # already seen
      ;;
    *)
      seen="$seen $word"
      ;;
  esac
done
echo $seen