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a function to find the fastest DNS server
http://public-dns.info gives a list of online dns servers. you need to change the country in url (br in this url) with your country code. this command need some time to ping all IP in list.

Insert the last argument of the previous command
for example if you did a: $ ls -la /bin/ls then $ ls !$ is equivalent to doing a $ ls /bin/ls

Hardlink all identical files in the current directory (regain some disk space)
Meaning of switches (see man page too): v verbose p ignore mode (permissions) o ignore owner, group t ignore time of modification Disadvantage: If you modify any linked file, this will propagate to all other files which occupy the same space.

Print every Nth line
Sometimes commands give you too much feedback. Perhaps 1/100th might be enough. If so, every() is for you. $ my_verbose_command | every 100 will print every 100th line of output. Specifically, it will print lines 100, 200, 300, etc If you use a negative argument it will print the *first* of a block, $ my_verbose_command | every -100 It will print lines 1, 101, 201, 301, etc The function wraps up this useful sed snippet: $ ... | sed -n '0~100p' don't print anything by default $ sed -n starting at line 0, then every hundred lines ( ~100 ) print. $ '0~100p' There's also some bash magic to test if the number is negative: we want character 0, length 1, of variable N. $ ${N:0:1} If it *is* negative, strip off the first character ${N:1} is character 1 onwards (second actual character).

Extract audio stream from an video file using mencoder
This command extracts the audio stream of the video in $file and stores it in a file where the original suffix is changed to .mp3

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"

Search some text from all files inside a directory

Find all active ip's in a subnet

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"

print character classes
Today I needed a way to print various character classes to use as input for a program I was writing. Also a nice way to visualize character classes.


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