s0sta
EN NL عربي
Filters
How to search
  • Plain words find names, texts and examples.
  • "two words" finds the exact phrase.
  • --name or -x finds an option.
  • #word looks only inside commands.
  • @grep finds lessons and labs that use grep.
  • Filters: cat:network · in:labs · in:notes · level:rhcsa · ch:8 · root:yes. Put ! before a word to leave it out. OR between words means one of them.
  • ↑ ↓ to move · Enter to open · Esc to close · / to search

curl

Send requests to URLs (HTTP, HTTPS, FTP …): test web servers, call APIs, download files, check TLS.

Level
Everyday Linux
Group
Web
Needs root
No
Package
curl

What it does

curl URL prints the answer of a server. With options you choose the method (-X), send headers (-H) and data (-d), follow redirects (-L), save to a file (-o), and see headers (-I, -i) or the full talk with the server (-v).

It is the tool to test a web server on the RHCSA exam (curl http://localhost) and the daily tool for REST APIs in DevOps.

curl has more than 250 options. This page lists the ones admins use most; see all with curl --help all.

How to write it

curl [OPTION]... URL...

Options 57

Most used

Request

-X, --request METHOD
The HTTP method: GET, POST, PUT, DELETE, PATCH …
-H, --header "NAME: VALUE"
Add a header.
-d, --data DATA
Send data with POST (@file reads a file).
--data-raw DATA
Send data; @ has no special meaning.
--data-binary DATA
Send data exactly as it is.
--data-urlencode DATA
URL-encode the data.
--json DATA
Send JSON (sets Content-Type and Accept).
-F, --form NAME=CONTENT
Send a form (multipart), file=@path uploads a file.
-G, --get
Put -d data in the URL as a query string.
-T, --upload-file FILE
Upload a file (PUT).
-A, --user-agent TEXT
Set the User-Agent.
-e, --referer URL
Set the Referer.
-u, --user USER[:PASSWORD]
Basic login (asks the password if not given).
--oauth2-bearer TOKEN
Send a bearer token.

Output

-o, --output FILE
Save to this file.
-O, --remote-name
Save with the name from the URL.
-J, --remote-header-name
Use the file name the server sends (with -O).
-i, --include
Show the response headers with the body.
-I, --head
Get only the headers (HEAD request).
-D, --dump-header FILE
Save the headers to a file.
-s, --silent
No progress bar and no errors.
-S, --show-error
Show errors even with -s.
-v, --verbose
Show the whole request and response, also TLS.
-w, --write-out FORMAT
Print data after the transfer, like %{http_code}.
--trace FILE
Full trace with data.
-#, --progress-bar
Simple progress bar.
--create-dirs
Make local folders for -o.

Connection

-L, --location
Follow redirects.
--max-redirs N
Maximum redirects.
-m, --max-time SECONDS
Stop after this many seconds.
--connect-timeout SECONDS
Maximum time to connect.
--retry N
Try again N times on errors.
-x, --proxy [PROTOCOL://]HOST[:PORT]
Use a proxy.
--noproxy LIST
Hosts that do not use the proxy.
--resolve HOST:PORT:ADDRESS
Use this IP for the host (test before a DNS change).
--connect-to HOST1:PORT1:HOST2:PORT2
Connect to another host/port.
-4, --ipv4
Use IPv4 only.
-6, --ipv6
Use IPv6 only.
--interface NAME
Use this interface.
-C, --continue-at OFFSET
Continue a download (-C - = automatic).
--limit-rate SPEED
Limit the speed, like 1M.
-Z, --parallel
Do transfers in parallel.

TLS

-k, --insecure
Do not check the certificate (tests only).
--cacert FILE
Trust this CA file.
--cert FILE[:PASSWORD]
Client certificate.
--key FILE
Private key of the client certificate.
--tlsv1.2, --tlsv1.3
Use at least this TLS version.
--http1.1, --http2, --http3
Use this HTTP version.

Errors and others

-f, --fail
Exit with an error (22) on HTTP errors, no body.
--fail-with-body
Like -f but print the body.
-n, --netrc
Read login data from ~/.netrc.
-K, --config FILE
Read options from a file.
-q, --disable
Do not read ~/.curlrc (must be first).
-h, --help [CATEGORY]
Show help (--help all for every option).
-V, --version
Show the version and protocols.

Examples 12

$ run as a normal user# run as root (or with sudo)

  1. 1Test a web server

    curl http://localhost

    RHCSA: check that httpd serves the page.

  2. 2Only the headers

    curl -I https://s0sta.com
HTTP/2 200
content-type: text/html; charset=UTF-8
strict-transport-security: max-age=31536000

    Check status code and security headers.

  3. 3Only the status code

    curl -s -o /dev/null -w '%{http_code}\n' https://s0sta.com
200

    Good for health checks and scripts.

  4. 4Follow redirects

    curl -sIL http://s0sta.com | grep -iE '^(HTTP|location)'

    Shows the chain http → https.

  5. 5Download a file

    curl -LO https://example.com/tool.tar.gz

    Saves as tool.tar.gz. Check the checksum afterwards.

  6. 6Call a JSON API

    curl -s -H "Authorization: Bearer $TOKEN" https://api.example.com/v1/servers | jq '.[].name'

    Keep tokens in variables or files, not in the history.

  7. 7Send JSON with POST

    curl -s -X POST -H 'Content-Type: application/json' -d '{"name":"web1"}' https://api.example.com/v1/servers

    Or shorter: --json '{"name":"web1"}'.

  8. 8Test a site on a new server before the DNS change

    curl -sI --resolve s0sta.com:443:203.0.113.20 https://s0sta.com

    Uses the new IP with the real name and certificate.

  9. 9See the TLS handshake and certificate

    curl -sv https://s0sta.com -o /dev/null 2>&1 | grep -E 'SSL connection|subject:|expire date'

    Check TLS version and expiry.

  10. 10Measure response times

    curl -s -o /dev/null -w 'dns %{time_namelookup}s connect %{time_connect}s total %{time_total}s\n' https://s0sta.com

    Find out if DNS, the network or the app is slow.

  11. 11Fail in a script on HTTP errors

    curl -fsS https://example.com/health || echo "health check failed"

    -f makes 404/500 an error (exit code 22).

  12. 12Check from inside a container network

    podman run --rm registry.access.redhat.com/ubi10/ubi curl -sI http://web:8080

    Tests service-to-service access.

Watch out

  • -k turns off certificate checks: never in production scripts.
  • curl URL | bash runs code from the internet without a check. Download, read, then run.
  • Passwords with -u user:pass show up in the process list and history.

Files

~/.curlrc
Default options.
~/.netrc
Login data for -n.

Exit codes

0 :: Done. 6 :: Could not resolve the host. 7 :: Could not connect. 22 :: HTTP error with -f. 28 :: Timeout. 35 :: TLS handshake failed. 60 :: The certificate could not be checked.

Full manual

This page explains the command in simple words. The original manual has every detail.

In your terminal: man curl

Open the man page (linux.die.net)curl.se