What is the meaning of "spawn" linux shell commands ? (Centos6)

I need to know how to setup a cron job that automatically connects to the remote server and change the directory and get all the files in that directory to local

i think i have to use sftp but i saw some commands called "spawn" in the some shell scripts and i am confused what this will do and what is for ?

spawn  sftp user@ipaddress
cd xxx/inbox
mget *

will this work in the context of the downloading remote directory ?

Solution 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+++