Do any of my techie readers have an idea about how to solve the following problem in a simple manner? (Or what would be a good place to ask, e.g. a news group that hasn't fallen out of use or something like Perl Monks?)

Once a day, I back up my del.icio.us bookmarks with the following:

wget -q -t1 --http-user=josephgrossberg --http-passwd=password -O foo.txt http://del.icio.us/api/posts/all

However if, for some reason, there is an empty response (e.g. del.icio.us is down), my file is overwritten with nothing.

After reading through some man pages, I found the promising --no-run-if-empty option for xargs:

If the standard input does not contain any non blanks, do not run the command. Normally, the command is run once even if there is no input.

I tested it out and something like echo "joe" | xargs --no-run-if-empty echo > foo.txt behaved correctly (it wrote to the file), as did echo "" | xargs --no-run-if-empty echo > foo.txt (it did not write to the file).

However, this still doesn't work with wget:

wget -q -t1 --http-user=josephgrossberg --http-passwd=password http://del.icio.us/api/posts/all | xargs --no-run-if-empty echo > foo.txt

The foo.txt file gets overwritten with 0 bytes.

Now, I suppose there could be something "obvious" I'm missing, but is there any canonical UNIX way to solve this problem other than writing a full-fledged bash script or piping it to Perl or the like?

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