How to use curl to download files efficiently?

curl (Client URL) is an open-source command-line tool that supports multiple network protocols (such as HTTP, HTTPS, and FTP) and is widely used for data transmission and file downloads. Its core function is to interact with servers through simple commands, making it particularly suitable for scenarios requiring automation or batch operations. For developers, operations personnel, and data analysts, mastering curl download techniques can significantly improve work efficiency.

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Basic operations of curl to download files

Basic download commands

Use the curl -O [URL] command to download a file directly to the current directory. For example, if you enter curl -O https://example.com/file.zip, the system automatically saves the file and retains the original name. To customize the file name, use the -o parameter, such as curl -o custom_name.zip https://example.com/file.zip.

Supported protocols and redirection

By default, curl supports HTTP/HTTPS, but can also be expanded to FTP or SFTP via parameters. If the target link has a redirect (such as a short link jump), adding the -L parameter will automatically follow the jump path to complete the download.

Resuming downloads and speed limiting

The -C - parameter enables curl to resume downloads, preventing repeated downloads due to network interruptions. To limit the download speed to prevent excessive bandwidth usage, use the --limit-rate parameter. For example, --limit-rate 500k limits the download speed to 500KB/s.

Advanced techniques to improve curl download efficiency

Multithreading and parallel downloading

Although curl itself doesn't support multithreading, you can use it with xargs or scripts to enable parallel downloads. For example, you can save multiple file URLs to a text file and use the command "cat urls.txt | xargs -n 1 -P 4 curl -O" to start four parallel processes to speed up the download.

Automation scripts and scheduled tasks

By calling curl commands through Shell scripts or Python, you can implement scheduled downloads, log records, and error retries. For example, combined with cron scheduled tasks, you can automatically capture updated data daily.

Integrated application of proxy IP

To bypass regional restrictions or circumvent anti-crawling mechanisms, you can configure a proxy IP for curl using the --proxy parameter. For example, you can use a static ISP proxy to ensure long-term IP stability, or a dynamic proxy to rotate IPs and reduce the risk of being blocked.

Common Problems and Solutions

Download speed is too slow

Check network connectivity: Use ping or traceroute to confirm the reachability of the target server.

Change the download source: Some mirror sites may provide faster download speeds.

Enable compressed transmission: Add the --compressed parameter to enable server-side compression to reduce the amount of data transmitted.

SSL certificate verification failed

If you encounter a certificate error (such as an SSL certificate problem), you can skip verification by using the -k or --insecure parameter, but this will reduce security. We recommend first checking the integrity of the system certificate library or using a trusted proxy service to forward requests.

Large file downloads interrupted

Use the -C - parameter to resume downloading, or use the tail -c command to manually calculate the number of downloaded bytes and resume the download progress.

Optimize curl download scenarios by combining proxy IP

Data collection and crawling: Avoid target website bans through dynamic residential proxy IP rotation.

International file synchronization: Use exclusive data center proxies to ensure stable international transmission.

Privacy protection: Static ISP proxy can hide your real IP and prevent your downloading behavior from being tracked.

As a lightweight download tool, curl has become an indispensable tool for developers due to its flexibility and cross-platform nature. Through parameter optimization and script extensions, users can easily handle a variety of needs, from simple single-file downloads to complex batch tasks.

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