Sox

I am looking for command-line utility that monitors the microphone, and if you start to speak, writes the file. Recording period should be adjusted.

Solution is:

   sox -t alsa default recording.wav silence 1 0.1 5% 1 1.0 5%

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http://www.thegeekstuff.com/2009/05/sound-exchange-sox-15-examples-to-manipulate-audio-files/