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Watch contents of a file grow
In this case, I'm keeping an eye on /var/log/messages, but of course any file will do. When I'm following a file, I generally don't want to see anything other than what has been added due to the command or service I've executed. This keeps everything clean and tidy for troubleshooting.

Length of longest line of code
Here's an awk version.

back ssh from firewalled hosts
host B (you) redirects a modem port (62220) to his local ssh. host A is a remote machine (the ones that issues the ssh cmd). once connected port 5497 is in listening mode on host B. host B just do a ssh 127.0.0.1 -p 5497 -l user and reaches the remote host'ssh. This can be used also for vnc and so on.

Show webcam output
Show the webcam output with mplayer.

escape any command aliases
e.g. if rm is aliased for 'rm -i', you can escape the alias by prepending a backslash: rm [file] # WILL prompt for confirmation per the alias \rm [file] # will NOT prompt for confirmation per the default behavior of the command

Concatenates lines using sed

Efficiently print a line deep in a huge log file
Sed stops parsing at the match and so is much more effecient than piping head into tail or similar. Grab a line range using $ sed '999995,1000005!d' < my_massive_file

check the status of 'dd' in progress (OS X)
Your platform may not have pv by default. If you are using Homebew on OSX, simply 'brew install pv'.

Throttle download speed (at speed x )
Throttle download speed $aria2c --max-download-limit=100K file.metalink Throttle upload speed $aria2c --max-upload-limit=100K file.torrent

Get AWS temporary credentials ready to export based on a MFA virtual appliance
You might want to secure your AWS operations requiring to use a MFA token. But then to use API or tools, you need to pass credentials generated with a MFA token. This commands asks you for the MFA code and retrieves these credentials using AWS Cli. To print the exports, you can use: `awk '{ print "export AWS_ACCESS_KEY_ID=\"" $1 "\"\n" "export AWS_SECRET_ACCESS_KEY=\"" $2 "\"\n" "export AWS_SESSION_TOKEN=\"" $3 "\"" }'` You must adapt the command line to include: * $MFA_IDis ARN of the virtual MFA or serial number of the physical one * TTL for the credentials


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