bash.sh

# the first case is the easiest, we're just reading a plain text file
$ cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
...

# now here, we think we're reading a file but we are not! (technically yes.. anyway)
$ cat /proc/meminfo
MemTotal:        2046844 kB
MemFree:          546984 kB
MemAvailable:    1535688 kB
Buffers:          162676 kB
Cached:           892000 kB
 
# and finally we open a file (using fd=3) for read/write
# the "file" being a socket, we then send a request to this file >&3
# and we read from this same "file"
$ exec 3<> /dev/tcp/www.google.com/80
$ printf 'HEAD / HTTP/1.1\nHost: www.google.com\nConnection: close\n\n' >&3
$ cat <&3
HTTP/1.1 200 OK
Date: Wed, 21 Aug 2019 12:48:40 GMT
Expires: -1
Cache-Control: private, max-age=0
Content-Type: text/html; charset=ISO-8859-1
P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info."
Server: gws
X-XSS-Protection: 0
X-Frame-Options: SAMEORIGIN
Set-Cookie: 1P_JAR=2019-08-21-12; expires=Fri, 20-Sep-2019 12:48:40 GMT; path=/; domain=.google.com
Set-Cookie: NID=188=K69nLKjqge87Ymv4h-gAW_lRfLCo7-KrTf01ULtY278lUUcaNxlEqXExDtVB104pdA8CLUZI8LMvJv26P_D8RMF3qCDzLTpjji96B9v_miGlZOIBro6pDreHP0yW7dz-9myBfOgdQjroAc0wWvOAkBu-zgFW_Of9VpK3IfIaBok; expires=Thu, 20-Feb-2020 12:48:40 GMT; path=/; domain=.google.com; HttpOnly
Accept-Ranges: none
Vary: Accept-Encoding
Connection: close