How to enable SFTP Support in cURL?

You have to compile curl with sftp support first.

Download and unpack the curl source. After that:

sudo apt-get install build-essential debhelper libssh2-1-dev
sudo apt-get source libcurl3
sudo apt-get build-dep libcurl3

cd curl-x.xx.x/debian

nano rules

find and replace "--without-libssh2" with "--with-libssh2"

cd ..

sudo dpkg-buildpackage

cd ..

sudo dpkg -i curl_xxxxx.deb
sudo dpkg -i libcurl3_xxxx.deb
sudo dpkg -i libcurl3-gnutls_xxxx.deb

Update the commands with the adequate versions, ofcourse. More info here.

If you can't find --without-libssh2 to replace with --with-libssh2 you can search for --without-ssl and append --with-libssh2, tested with curl Version 7.35.0 on Ubuntu 14.04.2

Customized answer from Frantique:

Download and unpack the curl source. After that:

sudo apt-get install build-essential debhelper libssh2-1-dev
sudo apt-get source libcurl3
sudo apt-get build-dep libcurl3

cd curl-*/debian

nano rules

Find --without-ssl and append --with-libssh2, in my case, it looks like this:

Before

cd debian/build && dh_auto_configure ${CONFIGURE_ARGS}          \
        --with-ca-path=/etc/ssl/certs
cd debian/build-gnutls &&  dh_auto_configure ${CONFIGURE_ARGS}  \
        --with-ca-bundle=/etc/ssl/certs/ca-certificates.crt     \
        --without-ssl --with-gnutls
cd debian/build-nss && dh_auto_configure ${CONFIGURE_ARGS}      \
        --with-ca-bundle=/etc/ssl/certs/ca-certificates.crt     \
        --without-ssl --with-nss

After

cd debian/build && dh_auto_configure ${CONFIGURE_ARGS}          \
        --with-ca-path=/etc/ssl/certs --with-libssh2
cd debian/build-gnutls &&  dh_auto_configure ${CONFIGURE_ARGS}  \
        --with-ca-bundle=/etc/ssl/certs/ca-certificates.crt     \
        --without-ssl --with-gnutls --with-libssh2
cd debian/build-nss && dh_auto_configure ${CONFIGURE_ARGS}      \
        --with-ca-bundle=/etc/ssl/certs/ca-certificates.crt     \
        --without-ssl --with-nss --with-libssh2

Now build the packages:

cd ..
sudo dpkg-buildpackage
cd ..

sudo dpkg -i curl_*.deb
sudo dpkg -i libcurl3_*.deb
sudo dpkg -i libcurl3-gnutls_*.deb

Here is another good tutorial for your issue.

More info on Frantique's answer.

Frantique's answer worked for me - however when I tried to upgrade my system, my package manager wanted to revert the installation back to a curl that does not have sftp/scp.

To avoid having to reinstall curl with sftp/scp after every upgrade:

sudo aptitude hold libcurl3
sudo aptitude hold libcurl3-gnutls

Use apt-mark if you use apt.

Read this page if you want more info on preventing updates of a specific package.

Note that eventually some future upgrade may not be able to go forward until you remove the hold.

If by chance you are using PHP and need sftp in curl - you should check out phpseclib which might be much easier to install and maintain.