Commands by dan (5)

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Insert a line at the top of a text file without sed or awk or bash loops
Yet another way to add a line at the top a of text file with the help of the tac command (reverse cat).

Terminal - Show directories in the PATH, one per line with sed and bash3.X `here string'
another method : awk '{gsub(/:/, "\n");print}'

Set laptop display brightness
Run as root. Path may vary depending on laptop model and video card (this was tested on an Acer laptop with ATI HD3200 video). $ cat /proc/acpi/video/VGA/LCD/brightness to discover the possible values for your display.

Send an http HEAD request w/curl

Recursive find and replace file extension / suffix (mass rename files)
Find recursively all files in ~/Notes with the extension '.md' and pipe that via xargs to rename command, which will replace every '.md' to '.txt' in this example (existing files will not be overwritten).

How to backup hard disk timely?
Creates files in $DATE and hardlinks existing files to $PREVDATE. Thus full backup in each directory. Only drawback is changed modification time. Recommend a wrapper script to determine $DATE and $PREVDATE. Works like a charm. (Dirvish handrolled)

Use /dev/full to test language I/O-failsafety
The Linux /dev/full file simulates a "disk full" condition, and can be used to verify how a program handles this situation. In particular, several programming language implementations do not print error diagnostics (nor exit with error status) when I/O errors like this occur, unless the programmer has taken additional steps. That is, simple code in these languages does not fail safely. In addition to Perl, C, C++, Tcl, and Lua (for some functions) also appear not to fail safely.

Create new user with home dir and given password
The crypt function takes a password, key, as a string, and a salt character array which is described below, and returns a printable ASCII string which starts with another salt. It is believed that, given the output of the function, the best way to find a key that will produce that output is to guess values of key until the original value of key is found. from http://en.wikipedia.org/wiki/Crypt_(Unix)

Make ogg file from wav file
Make ogg file from wav file

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"


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