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concatenate compressed and uncompressed logs
I use zgrep because it also parses non gzip files. With ls -tr, we parse logs in time order. Greping the empty string just concatenates all logs, but you can also grep an IP, an URL...

The simplest way to transport information over a network
Einstein's razor: As simple as possible, but not simpler. On the destination machine netcat listens on any port (1234 in the example) and sends anything it receives into a file or pipe. On the source machine a separate netcat takes input from a file or pipe and sends it over the network to the listener. This is great between machines on a LAN where you don't care about authentication, encryption, or compression and I would recommend it for being simpler than anything else in this situation. Over the internet you should use something with better security.

Encrypted archive with openssl and tar
command to decrypt: $ openssl enc -aes-256-cbc -d < secret.tar.enc | tar x Of course, don't forget to rm the original files ;) You may also want to look at the openssl docs for more options.

Convert "man page" to text file
You can convert any UNIX man page to .txt

Tunnel ssh through Socks Proxy
If you are blocked or need to use a Socks proxy

Copy something to multiple SSH hosts with a Bash loop
Just a quick and simple one to demonstrate Bash For loop. Copies 'file' to multiple ssh hosts.

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"

Shows what processes need to be restarted after system upgrade
emerge,apt-get,yum... all update your system. This will at some point replace either a runtime dependency or a process (which is still running). This oneliner will list what processes need to be restarted

extract email adresses from some file (or any other pattern)
find all email addresses in a file, printing each match. Addresses do not have to be alone on a line etc. For example you can grab them from HTML-formatted emails or CSV files, etc. Use a combination of $...|sort|uniq$ to filter them.

Expand shortened URLs
curl(1) is more portable than wget(1) across Unices, so here is an alternative doing the same thing with greater portability. This shell function uses curl(1) to show what site a shortened URL is pointing to, even if there are many nested shortened URLs. This is a great way to test whether or not the shortened URL is sending you to a malicious site, or somewhere nasty that you don't want to visit. The sample output is from: $ expandurl http://t.co/LDWqmtDM


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