Apps Artificial Intelligence CSS DevOps Go JavaScript Laravel Linux MongoDB MySQL PHP Python Rust Svelte Vue

Mastering `curl` on Linux: Downloads and API Requests

1 min read .
Updated on
Mastering `curl` on Linux: Downloads and API Requests

curl is one of the most useful command-line tools for transferring data and testing HTTP APIs. It supports HTTP, HTTPS, FTP, and many other protocols, making it useful for downloads, automation, diagnostics, and API development.

1. Check or Install curl

Check the installed version:

curl --version

On Debian or Ubuntu:

sudo apt update
sudo apt install curl

Other distributions provide curl through their normal package managers.

2. Download Files

Save a remote file using the filename from the URL:

curl -O https://example.com/file.zip

If the URL redirects, add -L:

curl -LO https://example.com/file.zip

Choose your own output filename with lowercase -o:

curl -o custom-name.zip https://example.com/file.zip

Resume a partially downloaded file:

curl -C - -O https://example.com/file.zip

3. Inspect HTTP Responses

Request only the response headers:

curl -I https://example.com

For more diagnostic detail about the connection and request, use verbose mode:

curl -v https://example.com

4. Send Form Data

-d sends a request body and causes curl to use POST unless another method is specified:

curl -d "param1=value1&param2=value2" https://example.com/api

You normally do not need -X POST when using -d.

5. Send JSON

Modern curl versions support the convenient --json option:

curl --json '{"key":"value"}' https://example.com/api

A widely compatible equivalent is:

curl -H "Content-Type: application/json" \
  -d '{"key":"value"}' \
  https://example.com/api

6. Authentication

Basic authentication:

curl -u username https://example.com/private

curl will prompt for the password, which is preferable to putting a password directly in shell history.

Bearer token authentication:

curl -H "Authorization: Bearer YOUR_TOKEN" https://example.com/api

Avoid committing real tokens to scripts or repositories. Prefer environment variables or a secret-management system for automation.

7. Cookies and Redirects

Save cookies:

curl -c cookies.txt https://example.com

Send stored cookies:

curl -b cookies.txt https://example.com

Follow redirects:

curl -L https://example.com

8. Check an HTTP Status Code in a Script

#!/usr/bin/env bash
url="https://example.com"
status_code=$(curl -o /dev/null -sS -w "%{http_code}" "$url")
printf 'Status code: %s\n' "$status_code"

For scripts that should fail on HTTP errors, consider --fail or --fail-with-body depending on the behavior you need.

Conclusion

curl covers far more than simple downloads. With a small set of options you can inspect HTTP responses, send form or JSON data, authenticate to APIs, manage cookies, follow redirects, and automate health checks from the shell.

Linux

Related Posts

Compress and Extract Files Quickly on Linux
Updated on
Compress and Extract Files Quickly on Linux
Linux provides several standard compression tools. Some compress a single file, while tar combines many files into one archive and can apply compression at the same time. gzip Copy gzip filename gunzip filename.gz gzip is widely available and usually a good balance between speed and compression ratio.
Linux
Count Files in a Linux Directory Quickly
Updated on
Count Files in a Linux Directory Quickly
Counting files is useful in shell scripts, backups, log maintenance, migration checks, and filesystem monitoring. The right command depends on whether you want only regular files, recursive results, hidden files, directories, or symbolic links. Count Regular Files in One Directory With GNU find: Copy find /path/to/directory -maxdepth 1 -type f -printf '.' | wc -c -maxdepth 1 prevents recursion into subdirectories. Hidden files are included automatically.
Linux
Create Cron Jobs on Linux
Updated on
Create Cron Jobs on Linux
Cron is a time-based scheduler commonly used on Linux and Unix-like systems. It can run backups, cleanup scripts, reports, maintenance commands, and other recurring tasks automatically. Cron Syntax A user crontab entry has five schedule fields followed by the command: Copy * * * * * /path/to/command - - - - - | | | | | | | | | +----- day of week (0-7, Sunday=0 or 7) | | | +------- month (1-12) | | +--------- day of month (1-31) | +----------- hour (0-23) +------------- minute (0-59) Edit Your User Crontab Copy crontab -e For example, run a backup every day at 02:30:
Linux
Create and Manage Symbolic Links on Linux
Updated on
Create and Manage Symbolic Links on Linux
A symbolic link, or symlink, is a special filesystem entry that stores a path to another file or directory. Symlinks are useful for shortcuts, shared configuration, version switching, and keeping one canonical copy of data. Create a Symlink Copy ln -s TARGET LINK_NAME Link to a file:
Linux
Display a Directory Tree on Linux
Updated on
Display a Directory Tree on Linux
A directory tree makes project and filesystem structure easier to understand than a flat list of paths. The dedicated tree utility is usually the clearest tool for this job. Use tree Copy tree Example output: Copy . └── folder1 ├── subfolder1 │ └── file1.txt └── subfolder2 └── file2.txt Include hidden entries:
Linux
Find Recently Changed Files on Linux
Updated on
Find Recently Changed Files on Linux
Linux provides several ways to find files that were modified recently or to watch a directory for changes as they happen. Files Modified in the Last Hour Copy find /path/to/directory -type f -mmin -60 -mmin works in minutes. Files Modified in Recent Days Copy find /path/to/directory -type f -mtime -1 find /path/to/directory -type f -mtime -7 find’s -mtime is based on 24-hour periods, not calendar dates. Use precise timestamps or -newermt when calendar boundaries matter.
Linux
chevron-up