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delay execution of a command that needs lots of memory and CPU time until the resources are available
[ 2000 -ge "$(free -m | awk '/buffers.cache:/ {print $4}')" ] returns true if less than 2000 MB of RAM are available, so adjust this number to your needs. [ $(echo "$(uptime | awk '{print $10}' | sed -e 's/,$//' -e 's/,/./') >= $(grep -c ^processor /proc/cpuinfo)" | bc) -eq 1 ] returns true if the current machine load is at least equal to the number of CPUs. If either of the tests returns true we wait 10 seconds and check again. If both tests return false, i.e. 2GB are available and machine load falls below number of CPUs, we start our command and save it's output in a text file. The ( ( ... ) & ) construct lets the command run in background even if we log out. See http://www.commandlinefu.com/commands/view/3115/ .

Find the package that installed a command

awk date convert
Convert readable date/time with `date` command

Watch the disk fill up with change highlighting
If you add the -d flag each difference in the command's output will be highlighted. I also monitor individual drives by adding them to df. Makes for a nice thin status line that I can shove to the bottom of the monitor.

Create a persistent connection to a machine
Create a persistent SSH connection to the host in the background. Combine this with settings in your ~/.ssh/config: Host host ControlPath ~/.ssh/master-%r@%h:%p ControlMaster no All the SSH connections to the machine will then go through the persisten SSH socket. This is very useful if you are using SSH to synchronize files (using rsync/sftp/cvs/svn) on a regular basis because it won't create a new socket each time to open an ssh connection.

Run a command if file/directory changes
Example: $ runonchange /etc/nginx nginx -t Ignores vim temp files. Depends on 'inotify-tools' for monitoring of file changes. Alternative to tools like 'entr', 'watchr'.

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"

Show Mac OS X version information

Convert CSV to JSON
Replace 'csv_file.csv' with your filename.

Get mouse location (X,Y coordinates)


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