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Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Use Linux coding style in C program
put "-linux" option into $HOME/.indent.pro to make it default

Command Line to Get the Stock Quote via Yahoo
Retrieve the current stock price from Yahoo Finance. The output is simply the latest price (which could be delayed). If you want to look up stock for a different company, replace csco with your symbol.

port scan using parallel
It takes over 5 seconds to scan a single port on a single host using nmap $ time (nmap -p 80 192.168.1.1 &> /dev/null) real 0m5.109s user 0m0.102s sys 0m0.004s It took netcat about 2.5 minutes to scan port 80 on the class C $ time (for NUM in {1..255} ; do nc -w 1 -z -v 192.168.1.${NUM} 80 ; done &> /dev/null) real 2m28.651s user 0m0.136s sys 0m0.341s Using parallel, I am able to scan port 80 on the entire class C in under 2 seconds $ time (seq 1 255 | parallel -j255 'nc -w 1 -z -v 192.168.1.{} 80' &> /dev/null) real 0m1.957s user 0m0.457s sys 0m0.994s

Show which programs are listening on TCP ports
Alternative: $ ss -tlpn

Show line numbers in a text file

Go to parent directory of filename edited in last command

determine if tcp port is open
Requires netcat.

Check for Firewall Blockage.
This is just one method of checking to see if an IP is blocked via IP tables or CSF. Simple and to the point. Replace xx.xx.xx.xx with the IP you wish to check.

xargs for builtin bash commands
Similar to xargs -i, but works with builtin bash commands (rather than running "bash -c ..." through xargs)


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