Random Linux stuff

This is a growing collection of handy one liners that I've used from time to time but can never remember the syntax for

Slideshow one liner with ffmpeg

Create a slideshow in mp4 format from a bunch of images

ffmpeg -y -r 1/3 -framerate 1 -i %1d.jpg  -c:v libx264 -vf fps=5 -pix_fmt yuv420p out.mp4

Summary: String Manipulation and Expanding Variables

Generic bash syntas stuff that I often need to look up

${parameter:-defaultValue} 	Get default shell variables value
${parameter:=defaultValue} 	Set default shell variables value
${parameter:?"Error Message"} 	Display an error message if parameter is not set
${#var} 	Find the length of the string
${var%pattern} 	Remove from shortest rear (end) pattern
${var%%pattern} 	Remove from longest rear (end) pattern
${var:num1:num2} 	Substring
${var#pattern} 	Remove from shortest front pattern
${var##pattern} 	Remove from longest front pattern
${var/pattern/string} 	Find and replace (only replace first occurrence)
${var//pattern/string} 	Find and replace all occurrences
${!prefix*} 	Expands to the names of variables whose names begin with prefix.

${var,}
${var,pattern} 	Convert first character to lowercase.

${var,,}
${var,,pattern} 	Convert all characters to lowercase.

${var^}
${var^pattern} 	Convert first character to uppercase.

${var^^}
${var^^pattern} 	Convert all character to uppercase.. 

Copying with tar

Copy from cwd to destination using tar

tar cvf - . | (cd /<destination path>/; tar xvf -)

Quick Directory Count

Get a quick summary of the number of dirs and files under a path using dents rather than statting recursively