The Book of Secret Knowledge

Basic Request with Headers

Show response headers only, silently, ignoring SSL errors:

curl -Iks https://www.google.com

• -I: Show response headers only.
• -k: Insecure connection (ignore SSL).
• -s: Silent mode.

Advanced Request with Redirects and User-Agent

curl -Iks --location -X GET -A "x-agent" https://www.google.com

• --location: Follow redirects.
• -X: Set HTTP method.
• -A: Set User-Agent.

Request with Proxy

curl -Iks --location -X GET -A "x-agent" --proxy http://127.0.0.1:16379 https://www.google.com

• --proxy [socks5://|http://]: Set proxy server.

Resume a download

curl -o file.pdf -C - https://example.com/Aiju2goo0Ja2.pdf

• -o: Write output to file.
• -C: Resume the transfer.

Find external IP address

curl ipinfo.io
curl ipinfo.io/ip
curl icanhazip.com
curl ifconfig.me/ip ; echo

Repeat URL requests

Using brace expansion:

curl -ks https://example.com/?[1-20]

Using a shell loop:

for i in {1..20} ; do curl -ks https://example.com/ ; done

Quick snippets for common filesystem tasks:

• Backup a file: cp filename{,.orig}
• Empty/Truncate a file: >filename
• Delete files not matching an extension: rm !(*.foo|*.bar|*.baz)
• Pass multi-line string to a file: Use cat << __EOF__ (overwrites) or cat >> filename << __EOF__ (appends).
• Edit remote file via vim: vim scp://user@host//etc/fstab
• Create and enter directory: mkd() { mkdir -p "$@" && cd "$@"; }
• Rename uppercase to lowercase: rename 'y/A-Z/a-z/' *

# Quickly backup a file
cp filename{,.orig}

# Empty a file (truncate to 0 size)
>filename

# Delete all files in a folder that don't match a certain file extension
rm !(*.foo|*.bar|*.baz)

# Pass multi-line string to a file
cat > filename << __EOF__
data data data
__EOF__

# Edit a file on a remote host using vim
vim scp://user@host//etc/fstab

# Create a directory and change into it at the same time
mkd() { mkdir -p "$@" && cd "$@"; }

# Convert uppercase files to lowercase files
rename 'y/A-Z/a-z/' *

SSH Escape Sequences

While in an active session, use ~ followed by a character:

• ~. : Terminate connection.
• ~B : Send a BREAK to the remote system.
• ~C : Open a command line.
• ~R : Request rekey (SSH protocol 2 only).
• ~^Z: Suspend SSH.
• ~# : List forwarded connections.
• ~& : Background SSH.
• ~~ : Send the escape character itself.

Compare remote and local files

ssh user@host cat /path/to/remotefile | diff /path/to/localfile -

SSH through a jump host

ssh -t reachable_host ssh unreachable_host

Run a command on a remote host via file input

cat > cmd.txt << __EOF__
cat /etc/hosts
__EOF__

ssh host -l user $(<cmd.txt)

Key Management

• Get public key from private key: ssh-keygen -y -f ~/.ssh/id_rsa
• List all fingerprints in known_hosts: ssh-keygen -l -f .ssh/known_hosts

Explicit Authentication Methods

• Password only: ssh -o PreferredAuthentications=password -o PubkeyAuthentication=no user@remote_host
• Publickey only: ssh -o PreferredAuthentications=publickey -o PubkeyAuthentication=yes -i id_rsa user@remote_host

Port Forwarding

Local Port Forwarding (Access remote service via local port):

# Forward local 2250 to remote nmap.org:443
ssh -L 2250:nmap.org:443 localhost

Remote Port Forwarding (Expose local service to remote host):

# Forward local 9051 to remote db.d.x:5432 through node.d.y
ssh -nNT -R 9051:db.d.x:5432 node.d.y

• -n: Redirect stdin from /dev/null.
• -N: Do not execute a remote command.
• -T: Disable pseudo-terminal allocation.