• February 9, 2023

Curl Linux

curl command in Linux with Examples - GeeksforGeeks

curl command in Linux with Examples – GeeksforGeeks

curl is a command line tool to transfer data to or from a server, using any of the supported protocols (HTTP, FTP, IMAP, POP3, SCP, SFTP, SMTP, TFTP, TELNET, LDAP or FILE). curl is powered by Libcurl. This tool is preferred for automation, since it is designed to work without user interaction. curl can transfer multiple file at [options] [URL… ]URL: The most basic uses of curl is typing the command followed by the This should display the content of the URL on the terminal. The URL syntax is protocol dependent and multiple URLs can be written as sets like:curl one, two, three}
URLs with numeric sequence series can be written as:curl 1-20]
Progress Meter: curl displays a progress meter during use to indicate the transfer rate, amount of data transferred, time left -# -o curl –silent If you like a progress bar instead of meter, you can use the -# option as in the example above, or –silent if you want to disable it completely. Example:Options:-o: saves the downloaded file on the local machine with the name provided in the -o [file_name] [URL… ]
Example:curl -o Output:The above example downloads the file from FTP server and saves it with the name: This option downloads the file and saves it with the same name as in the -O [URL… ]
Example:curl -O –: This option resumes download which has been stopped due to some reason. This is useful when downloading large files and was -C – [URL… ]
Example:curl -C – -O limit-rate: This option limits the upper bound of the rate of data transfer and keeps it around the given value in –limit-rate [value] [URL]
Example:curl –limit-rate 1000K -O Output:The command limits the download to 1000K bytes. -u: curl also provides options to download files from user authenticated FTP -u {username}:{password} [FTP_URL]
Example:curl -u demo:password -O: This option helps to upload a file to the FTP -u {username}:{password} -T {filename} {FTP_Location}
If you want to append a already existing FTP file you can use the -a or –append option. –libcurl:This option is very useful from a developers perspective. If this option is appended to any cURL command, it outputs the C source code that uses libcurl for the specified option. It is the code similar to the command line [URL… ] –libcurl [filename]
Example:curl > –libcurl code. c
Output:The above example downloads the HTML and saves it into and the code in code. c file. The next command shows the first 30 lines of the code. -x, –proxy: curl also lets us use a proxy to access the -x [proxy_name]:[port] [URL… ]
If the proxy requires authentication, it can be used with the command:curl -u [user]:[password] -x [proxy_name]:[port] [URL… ]
Sending mail: As curl can transfer data over different protocols, including SMTP, we can use curl to send –url [SMTP URL] –mail-from [sender_mail] –mail-rcpt [receiver_mail] -n –ssl-reqd -u {email}:{password} -T [Mail text file]DICT protocol: The Libcurl defines the DICT protocol which can be used to easily get the definition or meaning of any word directly from the command [protocol:[dictionary_URL]:[word]
Example:curl dict
Output:Note: There are a number of other options provided by cURL which can be checked on the man page. The Libcurl library has been ported into various programming languages. It’s advisable to visit the individual project site for documentation.
curl(1) - Linux manual page - man7.org

curl(1) – Linux manual page – man7.org

curl(1) – Linux manual page
curl(1) Curl Manual curl(1)
NAME top curl – transfer a URL
SYNOPSIS top curl [options / URLs]
DESCRIPTION top curl is a tool to transfer data from or to a server, using one of
the supported protocols (DICT, FILE, FTP, FTPS, GOPHER, HTTP,
HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, POP3, POP3S, RTMP, RTMPS,
RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET or TFTP). The
command is designed to work without user interaction.
curl offers a busload of useful tricks like proxy support, user
authentication, FTP upload, HTTP post, SSL connections, cookies,
file transfer resume and more. As you will see below, the number
of features will make your head spin!
curl is powered by libcurl for all transfer-related features. See
libcurl(3) for details.
URL top The URL syntax is protocol-dependent. You’ll find a detailed
description in RFC 3986.
You can specify multiple URLs or parts of URLs by writing part
sets within braces and quoting the URL as in:
“one, two, three}”
or you can get sequences of alphanumeric series by using [] as
in:
“1-100]”
“001-100]” (with leading
zeros)
“a-z]”
Nested sequences are not supported, but you can use several ones
next to each other:
“1996-1999]/vol[1-4]/part{a, b, c}”
You can specify any amount of URLs on the command line. They will
be fetched in a sequential manner in the specified order. You can
specify command line options and URLs mixed and in any order on
the command line.
You can specify a step counter for the ranges to get every Nth
number or letter:
“1-100:10]”
“a-z:2]”
When using [] or {} sequences when invoked from a command line
prompt, you probably have to put the full URL within double
quotes to avoid the shell from interfering with it. This also
goes for other characters treated special, like for example ‘&’,
‘? ‘ and ‘*’.
Provide the IPv6 zone index in the URL with an escaped percentage
sign and the interface name. Like in
“[fe80::3%25eth0]/”
If you specify URL without protocol prefix, curl will attempt
to guess what protocol you might want. It will then default to
HTTP but try other protocols based on often-used host name
prefixes. For example, for host names starting with “ftp. ” curl
will assume you want to speak FTP.
curl will do its best to use what you pass to it as a URL. It is
not trying to validate it as a syntactically correct URL by any
means but is instead very liberal with what it accepts.
curl will attempt to re-use connections for multiple file
transfers, so that getting many files from the same server will
not do multiple connects / handshakes. This improves speed. Of
course this is only done on files specified on a single command
line and cannot be used between separate curl invocations.
OUTPUT top If not told otherwise, curl writes the received data to stdout.
It can be instructed to instead save that data into a local file,
using the -o, –output or -O, –remote-name options. If curl is
given multiple URLs to transfer on the command line, it similarly
needs multiple options for where to save them.
curl does not parse or otherwise “understand” the content it gets
or writes as output. It does no encoding or decoding, unless
explicitly asked to with dedicated command line options.
PROTOCOLS top curl supports numerous protocols, or put in URL terms: schemes.
Your particular build may not support them all.
DICT Lets you lookup words using online dictionaries.
FILE Read or write local files. curl does not support accessing
file URL remotely, but when running on Microsoft
Windows using the native UNC approach will work.
FTP(S) curl supports the File Transfer Protocol with a lot of
tweaks and levers. With or without using TLS.
GOPHER Retrieve files.
HTTP(S)
curl supports HTTP with numerous options and variations.
It can speak HTTP version 0. 9, 1. 0, 1. 1, 2 and 3 depending
on build options and the correct command line options.
IMAP(S)
Using the mail reading protocol, curl can “download”
emails for you. With or without using TLS.
LDAP(S)
curl can do directory lookups for you, with or without
TLS.
MQTT curl supports MQTT version 3. Downloading over MQTT equals
“subscribe” to a topic while uploading/posting equals
“publish” on a topic. MQTT support is experimental and TLS
based MQTT is not supported (yet).
POP3(S)
Downloading from a pop3 server means getting a mail. With
or without using TLS.
RTMP(S)
The Realtime Messaging Protocol is primarily used to
server streaming media and curl can download it.
RTSP curl supports RTSP 1. 0 downloads.
SCP curl supports SSH version 2 scp transfers.
SFTP curl supports SFTP (draft 5) done over SSH version 2.
SMB(S) curl supports SMB version 1 for upload and download.
SMTP(S)
Uploading contents to an SMTP server means sending an
email. With or without TLS.
TELNET Telling curl to fetch a telnet URL starts an interactive
session where it sends what it reads on stdin and outputs
what the server sends it.
TFTP curl can do TFTP downloads and uploads.
PROGRESS METER top curl normally displays a progress meter during operations,
indicating the amount of transferred data, transfer speeds and
estimated time left, etc. The progress meter displays number of
bytes and the speeds are in bytes per second. The suffixes (k, M,
G, T, P) are 1024 based. For example 1k is 1024 bytes. 1M is
1048576 bytes.
curl displays this data to the terminal by default, so if you
invoke curl to do an operation and it is about to write data to
the terminal, it disables the progress meter as otherwise it
would mess up the output mixing progress meter and response data.
If you want a progress meter for HTTP POST or PUT requests, you
need to redirect the response output to a file, using shell
redirect (>), -o, –output or similar.
This does not apply to FTP upload as that operation does not spit
out any response data to the terminal.
If you prefer a progress “bar” instead of the regular meter, -#,
–progress-bar is your friend. You can also disable the progress
meter completely with the -s, –silent option.
OPTIONS top Options start with one or two dashes. Many of the options require
an additional value next to them.
The short “single-dash” form of the options, -d for example, may
be used with or without a space between it and its value,
although a space is a recommended separator. The long “double-
dash” form, -d, –data for example, requires a space between it
and its value.
Short version options that don’t need any additional values can
be used immediately next to each other, like for example you can
specify all the options -O, -L and -v at once as -OLv.
In general, all boolean options are enabled with –option and yet
again disabled with –no-option. That is, you use the exact same
option name but prefix it with “no-“. However, in this list we
mostly only list and show the –option version of them. (This
concept with –no options was added in 7. 19. 0. Previously most
options were toggled on/off through repeated use of the same
command line option. )
–abstract-unix-socket (HTTP) Connect through an abstract Unix domain socket,
instead of using the network. Note: netstat shows the
path of an abstract socket prefixed with ‘@’, however the argument should not have this leading character.
Added in 7. 53. 0.
–alt-svc
(HTTPS) WARNING: this option is experimental. Do not use
in production.
This option enables the alt-svc parser in curl. If the
file name points to an existing alt-svc cache file, that
will be used. After a completed transfer, the cache will
be saved to the file name again if it has been modified.
Specify a “” file name (zero length) to avoid
loading/saving and make curl just handle the cache in
memory.
If this option is used several times, curl will load
contents from all the files but the last one will be used
for saving.
Added in 7. 64. 1.
–anyauth
(HTTP) Tells curl to figure out authentication method by
itself, and use the most secure one the remote site claims
to support. This is done by first doing a request and
checking the response-headers, thus possibly inducing an
extra network round-trip. This is used instead of setting
a specific authentication method, which you can do with
–basic, –digest, –ntlm, and –negotiate.
Using –anyauth is not recommended if you do uploads from
stdin, since it may require data to be sent twice and then
the client must be able to rewind. If the need should
arise when uploading from stdin, the upload operation will
fail.
Used together with -u, –user.
See also –proxy-anyauth, –basic and –digest.
-a, –append
(FTP SFTP) When used in an upload, this makes curl append
to the target file instead of overwriting it. If the
remote file doesn’t exist, it will be created. Note that
this flag is ignored by some SFTP servers (including
OpenSSH).
–aws-sigv4
(TLS) Tells curl to use the specified certificate file to
verify the peer. The file may contain multiple CA
certificates. The certificate(s) must be in PEM format.
Normally curl is built to use a default file for this, so
this option is typically used to alter that default file.
curl recognizes the environment variable named
‘CURL_CA_BUNDLE’ if it is set, and uses the given path as
a path to a CA cert bundle. This option overrides that
variable.
The windows version of curl will automatically look for a
CA certs file named ´´, either in the
same directory as, or in the Current Working
Directory, or in any folder along your PATH.
If curl is built against the NSS SSL library, the NSS PEM
PKCS#11 module () needs to be available for
this option to work properly.
(iOS and macOS only) If curl is built against Secure
Transport, then this option is supported for backward
compatibility with other SSL engines, but it should not be
set. If the option is not set, then curl will use the
certificates in the system and user Keychain to verify the
peer, which is the preferred method of verifying the
peer’s certificate chain.
(Schannel only) This option is supported for Schannel in
Windows 7 or later with libcurl 7. 60 or later. This option
is supported for backward compatibility with other SSL
engines; instead it is recommended to use Windows’ store
of root certificates (the default for Schannel).
If this option is used several times, the last one will be
used.
–capath


(TLS) Tells curl to use the specified certificate
directory to verify the peer. Multiple paths can be
provided by separating them with “:” (e. g.
“path1:path2:path3”). The certificates must be in PEM
format, and if curl is built against OpenSSL, the
directory must have been processed using the c_rehash
utility supplied with OpenSSL. Using –capath can allow
OpenSSL-powered curl to make SSL-connections much more
efficiently than using –cacert if the –cacert file
contains many CA certificates.
If this option is set, the default capath value will be
ignored, and if it is used several times, the last one
will be used.
–cert-status
(TLS) Tells curl to verify the status of the server
certificate by using the Certificate Status Request (aka.
OCSP stapling) TLS extension.
If this option is enabled and the server sends an invalid
(e. g. expired) response, if the response suggests that the
server certificate has been revoked, or no response at all
is received, the verification fails.
This is currently only implemented in the OpenSSL, GnuTLS
and NSS backends.
Added in 7. 41. 0.
–cert-type
(TLS) Tells curl what type the provided client certificate
is using. PEM, DER, ENG and P12 are recognized types. If
not specified, PEM is assumed.
See also -E, –cert, –key and –key-type.
-E, –cert
(TLS) Tells curl to use the specified client certificate
file when getting a file with HTTPS, FTPS or another SSL-
based protocol. The certificate must be in PKCS#12 format
if using Secure Transport, or PEM format if using any
other engine. If the optional password isn’t specified,
it will be queried for on the terminal. Note that this
option assumes a “certificate” file that is the private
key and the client certificate concatenated! See -E,
–cert and –key to specify them independently.
If curl is built against the NSS SSL library then this
option can tell curl the nickname of the certificate to
use within the NSS database defined by the environment
variable SSL_DIR (or by default /etc/pki/nssdb). If the
NSS PEM PKCS#11 module () is available then
PEM files may be loaded. If you want to use a file from
the current directory, please precede it with “. /” prefix,
in order to avoid confusion with a nickname. If the
nickname contains “:”, it needs to be preceded by “\” so

Frequently Asked Questions about curl linux

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