The shell script one-liner thread

This thread is for "clever" one-liners that help you accomplish something useful.

Example:

Code:

# Try to mount all attached storage volumes, and throw away any error messages
sh -c "awk '{print \$4}' /proc/partitions | xargs -I DEV pmount /dev/DEV 2> /dev/null"

# Try to unmount all attached volumes, throw out error messages
sh -c "awk '{print \$4}' /proc/partitions | xargs -I DEV pumount /dev/DEV 2> /dev/null"

Note that I'm using 'sh -c' here so that the command strings can be invoked by a program that won't necessarily spawn a shell; e.g. by a window manager, as a menu entry. I redirect STDERR to /dev/null so as not to pollute ~/.xsession-errors. Upshot is, I can now use a WM menu entry to mount (or unmount) all storage devices I've plugged in, bypassing the need for polkit/logind/udisks/gvfs/Thunar/etc; all that's needed is pmount.

Edit: actually this might be better doable as a one-line awk script, using system(). The quotes keep messing me up on that though.

Edit 2: the way to do it with awk is as follows:

Code:

# Mount
awk '/[0-9]+/ {system("pmount " $4 " 2> /dev/null")} ' /proc/partitions

# Unmount
awk '/[0-9]+/ {system("pumount " $4 " 2> /dev/null")} ' /proc/partitions

Remember that in awk, *spaces* are used for string concatenation!

Edit 3: removed leading spaces from regex, they're not necessary and may mess it up. Also note that this still won't work in Fluxbox due to the embedded braces.

 

Okay, this is a five-liner, but what the heck:

Code:

#!/bin/sh -
for host in $@; do
  dig $host | egrep '\sA\s' | awk '{print $5}' \
    | xargs -iADDR ufw allow out to ADDR
done

You feed it a list of domains as arguments, and it enables them in UFW. This way (assuming you've run 'ufw default reject outgoing' at some point), you can quickly build a whitelist of acceptable domains.

Edit: fixed it to work with aliases as well.

Edit 2: and similarly for deleting entries

Code:

#!/bin/sh -
for host in $@; do
  dig $host | egrep '\sA\s' | awk '{print $5}' \
    | xargs -iADDR ufw delete allow out to ADDR
done

Edit 3: I'll see if I can come up with something later for pruning wrong/unused IPs from the list...

 

Using dmenu as a fast directory browser - in this case, opening the target directory in gnome-terminal.

Code:

sh -c 'find . -type d | dmenu -i | xargs -iDIR gnome-terminal --working-directory=DIR'

I have this bound to Win-space.

 

Select a window in X, and instantly renice it from the default 0 to 1, reducing its CPU priority:

Code:

renice -n 1 $(xprop | awk '/PID/ {print $3}')

Edit: don't need grep before awk. D'oh!

 

Similar but better on multicore machines: select the window and lock its program to the second CPU core.

Code:

taskset -a -pc 1 $(xprop | awk '/PID/ {print $3}')

This seems to produce reasonable results wtih Qemu (both with and without KVM support). Can't say for Virtualbox yet.

 

I got a oneliner:

Code:

lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB" " " $9 " " $1 }' | sort -n -u | tail

Show the largest 10 currently open files, the size of those files in Megabytes, and the name of the process holding the file open.

 

Quickly encrypt a file with openssl (assuming that openssl is present in most, if not all linux distro's):

Code:

openssl aes-256-cbc -a -salt -in secret.txt -out secret.txt.enc

when you execute this command you will be prompted to enter a password.
a nice way to quickly encrypt a file maybe.
Replace "secret.txt" and "secret.txt.enc" with your own names of choice
To decrypt:

Code:

openssl aes-256-cbc -d -a -in secret.txt.enc -out secret.txt

 

For installing all the build dependencies of anything and everything on your Fedora (or CentOS, etc.) system:

Code:

rpm -qa | xargs -iX yum-builddep -y X

Be warned, this will use up a lot of disk space. (But it's probably worth it!)

 

I personally use gpg for this. You can do so with:

Code:

gpg --output doc.gpg --symmetric doc