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Are you trying to download a file from a Bash script but you are not sure where to start? Let me show you how to use wget, curl or download files with a shell script using Bash Redirections.
Generally you will want to use the pre-installed tool on your platform which is generally wget or curl.
Introduction to wget
GNU Wget is a free utility for non-interactive download of files from the Web. It supports HTTP, HTTPS, and FTP protocols, as well as retrieval through HTTP proxies.
One liner example: wget -O newname.txt http://www.het.brown.edu/guide/UNIX-password-security.txt
Introduction to curl
curl is a tool to transfer data from or to a server, using one of the supported protocols (HTTP, HTTPS, FTP, FTPS, TFTP, DICT, TELNET, LDAP or FILE). The command is designed to work without user interaction.
One liner example: curl -o newname.txt http://www.het.brown.edu/guide/UNIX-password-security.txt
Bash Redirections
Lastly, if you don’t have wget, curl or any similar command-line tool, you can use a pure shell script approach by using the /dev/tcp pseudo-device. Since Bash version 2, you can directly open a TCP connection to a given socket.
`/dev/tcp/HOST/PORT'
If HOST is a valid hostname or Internet address, and PORT is an
integer port number or service name, Bash attempts to open a TCP
connection to the corresponding socket.
Below is a sample bash script on how to download a file, from a non-secured HTTP endpoint, without using wget or curl. It defines a
bash function named _get and use the pseudo-device to open the TCP connection. You can add this function to your .bashrc for convenience.
_get ()
{
IFS=/ read proto z host query <<< "$1"
exec 3< /dev/tcp/$host/80
{
echo GET /$query HTTP/1.1
echo connection: close
echo host: $host
echo
} >&3
sed '1,/^$/d' <&3 > $(basename $1)
}
# Example usage
[me@linux ~]$ _get http://www.het.brown.edu/guide/UNIX-password-security.txt
[me@linux ~]$ ls
UNIX-password-security.txt
[me@linux ~]$ type _get
_get is a function
_get ()
{
IFS=/ read proto z host query <<< "$1";
exec 3< /dev/tcp/$host/80;
{
echo GET /$query HTTP/1.1;
echo connection: close;
echo host: $host;
echo
} 1>&3;
sed '1,/^$/d' 0<&3 > $(basename $1)
}
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