Transferring Files
Overview
Teaching: 10 min
Exercises: 0 minQuestions
How to use wget, curl and lftp to transfer file?
Objectives
FIXME
There are other ways to interact with remote files other than git.
It is true that we can clone an entire git repository, or even one level of a git repository using:
git clone --depth-1 repository_name.
What about files that do not exist in a git repository? If we wish to download files from the shell
we can use tools such as Wget, cURL, and lftp.
Wget
Wget is a simple tool developed for the GNU Project that downloads files with the HTTP, HTTPS and FTP protocols. It is widely used by Unix-like users and is available with most Linux distributions.
To download this lesson (located at http://swcarpentry.github.io/shell-extras/03-file-transfer.html) from the web via HTTP we can simply type:
$ wget http://swcarpentry.github.io/shell-extras/03-file-transfer.html
--2014-11-21 09:41:31--
http://swcarpentry.github.io/shell-extras/03-file-transfer.html
Resolving software-carpentry.org (software-carpentry.org)... 174.136.14.108
Connecting to software-carpentry.org (software-carpentry.org)|174.136.14.108|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 8901 (8.7K) [text/html]
Saving to: '03-file_transfer.html'
100%[======================================>] 8,901 --.-K/s in 0.05s
2014-11-21 09:41:31 (187 KB/s) - '03-file_transfer.html' saved [8901/8901]
Alternatively, you can add more options, which are in the form:
wget -r -np -D domain_name target_URL
where -r means recursively crawl to other files and directories, -np means avoid crawling to parent directories, and -D means to target only the following domain name
For our URL it would be:
$ wget -r -np -D software-carpentry.org http://swcarpentry.github.io/shell-extras/03-file-transfer.html
To restrict retrieval to a particular extension(s)
we can use the -A option followed by a comma separated list:
wget -r -np -D software-carpentry.org -A html http://swcarpentry.github.io/shell-extras/03-file-transfer.html
We can also clone a webpage with its local dependencies:
$ wget -mkq target_URL
We could also clone the entire website:
$ wget -mkq -np -D domain_name domain_name_URL
and add the -nH option if we do not want a subdirectory created for the websites content:
e.g.
$ wget -mkq -np -nH -D example.com http://example.com
where:
-m is for mirroring with time stamping, infinite recursion depth, and preservation of FTP directory settings
-k converts links to make them suitable for local viewing
-q supresses the output to the screen
The above command can also save the clone the contents of one domain to another if we are using ssh or sshfs to access a webserver.
Please refer to the man page by typing man wget in the shell for more information.
cURL
Alternatively, we can use cURL.
It supports a much larger range of protocols including common mail based protocols like pop3 and smtp.
To download this lesson (located at http://swcarpentry.github.io/shell-extras/03-file-transfer.html) from the web via HTTP we can simply type:
$ curl -o 10-file_transfer.html http://swcarpentry.github.io/shell-extras/03-file-transfer.html
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 14005 100 14005 0 0 35170 0 --:--:-- --:--:-- --:--:-- 105k
This input to curl is in the form:
curl -o filename_for_local_machine target_url
where the -o option says write the output to a file instead of the stdout (the screen),
and file_name_for_local_machine is any file name you choose to save to the local machine,
and target_URL is where the file is the URL where the file is on the web
Removing the -o option, and following the syntax curl target_URL
outputs the contents of the url to the screen.
If we wanted to enhance the functionality we have we could use information from the pipes and filters section,
which is lesson 4 from the unix shell session.
For example, we could type
curl http://swcarpentry.github.io/shell-extras/03-file-transfer.html | grep curl
which would tell us that indeed this URL contains the string curl.
We could make the output cleaner by limiting the output of curl to just the file contents by using the -s option
(e.g. curl -s http://swcarpentry.github.io/shell-extras/03-file-transfer.html | grep curl).
If we wanted only the text and not the html tags in our output we could use html to text parser such as html2text.
$ curl -s http://swcarpentry.github.io/shell-extras/03-file-transfer.html | html2text | grep curl
With wget, we can obtain the same results by typing:
$ wget -q -D swcarpentry.github.io -O /dev/stdout http://swcarpentry.github.io/shell-extras/03-file-transfer.html | html2text | grep curl
Wget offers more functionality natively than curl for retrieving entire directories.
We could use Wget to first retrieve an entire directory and then run html2text and grep
to find a particular string.
cURL is limited to retrieving one or more specified URLs that cannot be obtained by recursively crawling a directory.
The situation may be improved by combining with other unix tools, but is not thought as being as good as Wget.
Please refer to the man pages by typing man wget, man curl, and man html2text in the shell for more information.
lftp
Another option is lftp. It has a lot of capability, and even does simple bittorrent.
If we want to retrieve 03-file-transfer.html on the website and save it with the filename 03-file-transfer.html locally:
$ lftp -c get http://swcarpentry.github.io/shell-extras/03-file-transfer.html
If we want to print 03-file-transfer.html to the screen instead:
$ lftp -c cat http://swcarpentry.github.io/shell-extras/03-file-transfer.html
To obtain retrive all of the files with a particular extension in a directory we can type:
$ lftp -c mget {URL for directory}/*.extension_name
For example, to retrieve all of the .html files in the extras folder:
$ lftp -c mget http://swcarpentry.github.io/shell-extras/*.html
Please refer to the man page by typing man lftp in the shell for more information.
Key Points
FIXME