What is the meaning of the "spawn" command in Linux (Centos6)

Question

I need to know how to set up a cron job that automatically connects to a remote server, then changes to a directory and downloads all the files in that directory to local.

I think I have to use SFTP but I saw the following command using "spawn" in a shell script, and I am confused as to how it is used and why:

spawn  sftp user@ipaddress
cd xxx/inbox
mget *

Will this work to download a remote directory?

Answer 1

In your case, spawn is most probably a command of expect scripting language which allows automation of interactive program operations. In such a case, spawn runs an external command from the expect script. Your script example is missing a shebang sequence (first line starting with #!), indicating the expect interpreter, and, as such, will not be interpreted by expect when executed directly.

Password authentication with sftp is limited to the interactive mode; To control sftp in interactive mode, you can use the following expect script example:

#!/usr/bin/env expect
set timeout 20    # max. 20 seconds waiting for the server response

set user username
set pass your-pass
set host the-host-address
set dir  server-dir

spawn sftp $user@$host
expect assword:

send "$pass\r"
expect sftp>

send "cd $dir\r"
expect sftp>

send "mget *\r"
expect sftp>

send "exit\r"
expect eof

Another possibility is to use public-key authentication, which is more secure (see Setup SFTP to Use Public-Key Authentication). In such a case, you can simply use sftp directly in batch mode:

#!/bin/sh
user=username
host=the-host-address
dir=server-dir

sftp -b - "$user@$host" <<+++EOF+++
cd "$dir"
mget *
exit
+++EOF+++