How to check if the file is downloaded with curl

Question

I am writing a shell script, I need to download 6 files from internet, In the script I have done it as

curl a
curl b
curl c
and so on

It works, but sometimes curl: (7) couldn't connect to host for some files in the middle of script for example, It will successfully download a but miss the file b with the above error and will download the file c. I would like to catch this error so that my code will execute with the successful download of all the files.

Answer 1

You can use a loop:

while true; do
  curl --fail b && break
done

The loop won't break until b is downloaded. You can make it a retry function which you can call if a download fails on the first try:

retry(){
    while true; do
      curl --fail "$1" && break ||
      echo "Download failed for url: $1
            retrying..."
    done
}

Then do this:

curl --fail a || retry a
curl --fail b || retry b
curl --fail c || retry c

If you just want to silent the error messages then:

curl a 2>/dev/null
curl b 2>/dev/null
...

Or if you want to just detect the error then:

if ! curl --fail a; then
  echo "Failed"
fi

or, a one liner:

curl --fail a || echo Failed

If you want to exit after a failure and also show your own message:

curl --fail a 2>/dev/null || { echo failed; exit 1; }