Curl

curl(1) is a command-line tool for fetching internet (chiefly web or FTP) content.

The project (which encompasses both curl(1) and libcurl) is stylized as cURL, and stands for "Client URL".

Contents

Curl

Installation

All Linux and BSD distributions offer a curl package.

Usage

curl -output path/to/file URL

If the output option is not specified, the response will be written to STDOUT.

Tips

Suppressing Progress Bar

curl --no-progress-meter https://example.com

Downloading a File

curl --output path/to/file --fail https://example.com

In the case of a server error (HTTP 4xx), an error page is often returned by the server. The --fail option suppresses this page from output and causes curl(1) to exit with code 22.

Checking Availability

code=$(curl --silent --fail --head --write-out '%{http_code}' https://example.com)
case $code in
  0)
    echo "Success! Server returned HTTP code ${code}"
    ;;
  22)
    echo "Error! Server returned HTTP code ${code}"
    ;;
  6)
    echo "Error! Server not found"
    ;;
  60)
    echo "Error! SSL/TLS certificate cannot be verified"
    ;;
  *)
    echo "Error!"
    ;;
esac

The --head option causes curl(1) to only fetch only headers. The --silent option suppresses all output, including the progress bar or any returned pages.

The --write-out option takes a format string that will be populated with available variables.

Other useful variables:

Name	Contains
content_type	Content type of the document
http_version	Version of HTTP that was used
size_header	Number of bytes in downloaded headers
size_download	Number of bytes in downloaded body and data (i.e. not headers)
time_namelookup	Number of seconds from start until name was resolved
time_connect	Number of seconds from start until TCP connection
time_appconnect	Number of seconds from start until SSL handshake
time_pretransfer	Number of seconds from start until all pre-transfer steps are complete
time_starttransfer	Number of seconds from start until first transferred byte is received
time_total	Number of seconds
speed_download	Average number of bytes per second
ssl_verify_result	Result of certificate verification (0 if successful)