Execute command (function) from a variable in a script

Question

So, I want to create a script where I check sth from a website. I have a text file with different websites in it and I want to check all websites simultaneously. To do this I'm creating a command step by step in a variable calling a function which will check every website. This is my code:

checkWebsite(){
    WEBSITE="$2"
    echo "Parameter is $WEBSITE"
}

COUNTER=0;

input=websites.txt

myCommand=()
while IFS= read -r line
do
    if [[ "$line" != "#"* ]]; #ignoring comments if there are any
    then
        myCommand[COUNTER]="checkWebsite $line"
        COUNTER=$((COUNTER + 1))
        myCommand[COUNTER]=" & "
        COUNTER=$((COUNTER + 1))
    fi
done < "$input"

unset 'myCommand[${#myCommand[@]}-1]' #deleting the last " & "

echo "MY COMMAND: "
echo ${myCommand[@]}
echo " "

echo ${myCommand[0]}
checkWebsite ${myCommand[0]}
"${myCommand[0]}"

These are the results: results

As you can see, if I call the function from the script everything is ok but if I call the function from the variable it doesn't work. I understand why this is happening(it's like I run that command from the terminal) but I don't know how can I make it run the function from the script when I execute the command from the variable. Does anyone know how can I make that happen?

Thanks in advance

Putting it in a variable makes it harder and messier than it has to be. Is there a reason why you're not just running it directly? — that other guy
– that other guy, Commented Nov 24, 2018 at 20:08
Asked and answered a lot of times: bash command parameter substitution site:stackoverflow.com. Which would you like as your duplicate? — jww
– jww, Commented Nov 24, 2018 at 20:17
Also see BashFAQ #50. "${myCommand[0]}" entirely defeats the whole purpose of using an array -- dereffing just the first element means it's just another string. — Charles Duffy
– Charles Duffy, Commented Nov 24, 2018 at 20:19
BTW, declare -p myCommand gives you a much more accurate idea of your array's contents than echo ${myCommand[@]} does. (For that matter, printf '%q\n' "${myCommand[@]}" would be an improvement as well). — Charles Duffy
– Charles Duffy, Commented Nov 25, 2018 at 0:39

Charles Duffy · Accepted Answer · 2018-11-24 20:21:01Z

3

Don't use an array here. It causes a lot of trouble and adds no value whatsoever. Instead, start your background tasks inside the loop:

while IFS= read -r line; do
  [[ "$line" = "#"* ]] || checkWebsite "$line" &
done < "$input"

If you really want an array, populate it from the loop, and -- again -- start items individually without it.

websites=( )
while IFS= read -r line; do
  [[ "$line" = "#"* ]] || websites+=( "$line" )
done < "$input"

for site in "${websites[@]}"; do
  checkWebsite "$site" &
done

Why doesn't the other approach work? Because & only acts as a command separator when parsed as syntax, and parameter expansion results are data, not syntax.

You would need to use eval to make your expansion results parse as syntax; unless done with great care, this would cause serious security vulnerabilities.

answered Nov 24, 2018 at 20:21

Charles Duffy

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