only redirects to stdout if there is something to be redirected-CodePudding

I'm downloading a file from the web and I would like to redirect the file to stdout only if there is something printed to stdout, if not I would like to skip the redirection. This is because I have an if..then..else statement as follows:

if ! [[ -f data/worldcitiespop.csv ]]; then curl -L https://burntsushi.net/stuff/worldcitiespop.csv ; fi > data/worldcitiespop.csv 2> log

In case data/worldcitiespop.csv already exists and if i run this again the output will be empty. I don't want that, I want to leave it populated.

CodePudding user response：

You can store curl command output in a variable and check if there is a non-whitespace character in that variable before writing that variable content to output file:

if ! [[ -f data/worldcitiespop.csv ]]; then
   out=$(curl -L https://burntsushi.net/stuff/worldcitiespop.csv 2>log)
   [[ $out = *[![:space:]]* ]] && echo "$out" > data/worldcitiespop.csv
fi >