array assignment from command output in ksh

Question

I wanted to assign the output of a command to an array, but came across the following problem:

temp=`<some_command>`
eval set -A array $temp
print $temp
print "***${array[0]},${array[1]}***"

The command's output is something like:

""
"D"
"M"
"N"

In my expectation, ${array[0]} should be "", and ${array[1]} should be "D".

But, the following is the result:

" "D" "M" "N" # $temp
*** D M N,*** # ${array[0]},${array[1]}

Just can't figure out how the first element of the array sweeps all of the output. And how to fix it?

Update: Today, I took another look at the script, and found that the command's output is:

" "
"D"
"M"
"N"

Note the first line is " " (there is a space character in it), instead of a pure empty string "".

To start with, the original output was:

<some_command> |sort |uniq -c
6421 " "
1090 "D"
   1 "DPV_VALID"
   3 "M"
 588 "N"
  16 "S"
6382 "Y"

I always thought the first line was a pure empty string, e.g. "", didn't realize that there is a space character in the double quotes.

Then, I used awk to get the 2nd field:

<some_command> |sort |uniq -c |awk '{print $2}'

The output became:

"
"D"
"M"
"N"

That's the cause of later mess-up of the command eval set -A (awk uses space character as the delimiter by default). If it were a pure empty string, it would have worked.

It also works if I re-write the command as:

temp=`<some_command> |sort |uniq -c |sed 's/" "$/""/' |awk '{print $2}'`
eval set -A array $temp

Still, glenn's solution is also pretty neat. Thanks!

What value does $IFS hold when you set the array? Why do you think you need eval? — glenn jackman
– glenn jackman, Commented Apr 19, 2013 at 20:45
@glennjackman Sorry, what is $IFS? I need eval because I only want the content inside the double quotes. — Qiang Xu
– Qiang Xu, Commented Apr 19, 2013 at 22:33

glenn jackman · Accepted Answer · 2013-04-20 15:54:09Z

2

If you want to remove the quotes, just remove them. You don't have to resort to eval

temp='""
"D"
"M"
"N"'
set -A array $temp
for (( i=0; i<${#array[@]}; i++ )); do
    echo "$i:${array[i]}"
done
for (( i=0; i<${#array[@]}; i++ )); do
    array[i]=${array[i]#\"}   # remove a leading quote
    array[i]=${array[i]%\"}   # remove a trailing quote
done
for (( i=0; i<${#array[@]}; i++ )); do
    echo "$i:${array[i]}"
done

outputs

0:""
1:"D"
2:"M"
3:"N"
0:   
1:D
2:M
3:N

tested with ksh93

answered Apr 20, 2013 at 15:54

glenn jackman

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1 Comment

Qiang Xu Over a year ago

Thanks, this works! Still, I am not sure why eval would mess it up.

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