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Check variable has been set

Got the idea from there http://fixunix.com/questions/15902-bash-checking-if-env-var-set.html Show Sample Output
This is sample output - yours may be different.
```
$ isdef a_var; echo $?
1
$ a_var=1
$ isdef a_var; echo $?
0
```
0

isdef() { eval test -n \"\${$1+1}\"; }

keymon · 2011-09-29 15:39:51 3
Print heap addresses and size

Show Sample Output
This is sample output - yours may be different.
```
00014000-00174000 rwxp 00000000 00:00 0    [heap]
Size:    1408 kB
Rss:     1292 kB
```
0

PID=`ps | grep process_name | grep -v grep | head -n 1 | awk '{print $1}'`; cat /proc/$PID/smaps | grep heap -A 2

yohananov · 2012-01-30 13:31:40 3
Recursively sort files by modification time through multiple directories.
This is sample output - yours may be different.
0

find /test -type f -printf "%AY%Aj%AH%AM%AS---%h/%f\n" | sort -n

omatictost · 2012-10-25 16:22:48 4
Order all files oldest to newest then get the last one touched

On the Mac, the 'ls' function can sort based on month/day/time, but seems to lack ability to filter on the Year field (#9 among the long listed fields). The sorted list continuously increases the 'START' year for the most recently accessed set of files. The final month printed will be the highest month that appeared in that START year. The command does its magic on the current directory, and suitably discards all entries that are themselves directories. If you expect files dating prior to 2002, change the START year accordingly.
This is sample output - yours may be different.
0

ls -lT -rt | grep "^-" | awk 'BEGIN {START=2002} (START <= $9){ print $10 ;START=$9 }' | tail -1

Glamdring · 2013-02-24 23:39:22 7
Get the Nth argument of the last command in $HISTFILE

This gets the Nth argument in the last line of your history file. This is useful where history is being written after each command, and you want to use arguments from the previous command in the current command, such as when doing copies/moving directories etc. I wrote this after getting irritated with having to continually type in long paths/arguments. You could also use $_ if all you want is the last argument. Show Sample Output
This is sample output - yours may be different.
```
$ echo "This little piggy went to the market"
This little piggy went to the market
$ garg 5
went
```
0

function garg () { tail -n 1 ${HISTFILE} | awk "{ print \$$1 }" }

plasticphyte · 2013-09-10 04:07:46 10
one liner to rename files with for and sed

If you want to test output, run it like this: for fn in *.epub; do echo mv \"$fn\" \"`echo "$fn" | sed -E 's/\.*\/*(.*)( - )(.*)(\.[^\.]+)$/\3\2\1\4/' | sed -E 's/(.*) ([^ ]+)( - )(.*)/\2, \1\3\4/' `\";done > rename.txt Show Sample Output
This is sample output - yours may be different.
```
Input filename: The Big Wave - Pearl S. Buck.epub
Output: Buck, Pearl S. - The Big Wave.epub
```
0

for fn in *.epub; do echo mv \"$fn\" \"`echo "$fn" | sed -E 's/\.*\/*(.*)( - )(.*)(\.[^\.]+)$/\3\2\1\4/' | sed -E 's/(.*) ([^ ]+)( - )(.*)/\2, \1\3\4/' `\";done | sh

woohoo · 2013-11-30 05:29:52 6
Find directories in pwd, get disk usage, sort results
This is sample output - yours may be different.
0

du -a | sort -nr | head -10

compguy925 · 2014-06-10 13:00:27 8
drop first column of output by piping to this

drop first column with perl "$#F" means a index of last column(start from 0). One can easily handle range of columns like "[3..6]"
This is sample output - yours may be different.
0

perl -anE'say join "\t",@F[1..$#F]'

pung96 · 2015-05-09 15:11:23 9
Restart Plasma without logging off from KDE

This can help with serious GUI lockups in KDE. It will only restart Plasma + widgets, not your session, so all your programs will stay running.
This is sample output - yours may be different.
0

pkill plasma-desktop && plasma-desktop

lordtoran · 2015-09-28 23:36:24 12
Play Lisp Tetris in Emacs
This is sample output - yours may be different.
0

emacs -f tetris

steadystatic · 2015-11-03 23:35:32 10
Get current Xorg resolution via xrandr

if there are multiple monitors, this command uses multiple lines Show Sample Output
This is sample output - yours may be different.
```
1280x800
```
0

xrandr | awk '/*/ {print $1}'

misterhat · 2015-12-21 15:29:39 11
Remove all node_module folders recursively

makes sure not to skip children nodemodules credit: https://coderwall.com/p/guqrca/remove-all-node_module-folders-recursively
This is sample output - yours may be different.
0

find . -name "node_modules" -type d -prune -exec rm -rf '{}' +

ctcrnitv · 2018-02-10 04:23:36 22
conver mp3 to m4b
This is sample output - yours may be different.
0

mpg123 -s input.mp3 | faac -P -X -w -o output.m4b -

schmiddim · 2010-03-06 11:28:19 3
get value after comma from an arithmetic operation

scale define the number you want after comma Show Sample Output
This is sample output - yours may be different.
```
gnu@robby:~$ echo "scale=6;2048 / 2.345" | bc
873.347547
```
0

echo "scale=6;2048 / 2.345" | bc

eastwind · 2010-04-05 12:06:50 3
Indent all the files in a project using emacs

Use find's exec and reduce the need for multiple evals with a progn wrapper.
This is sample output - yours may be different.
0

find . -iname \*.c -or -iname \*.h -exec emacs -nw -q {} --eval "(progn (mark-whole-buffer) (indent-region (point-min) (point-max) nil) (save-buffer))" --kill \;

zev · 2010-09-10 05:07:11 3
Reading my nic's mac address

plain and simple Show Sample Output
This is sample output - yours may be different.
```
-bash-3.00$ /sbin/ifconfig | grep HWaddr
eth0      Link encap:Ethernet  HWaddr 00:50:56:9C:69:6F
eth1      Link encap:Ethernet  HWaddr 00:50:56:9C:16:C6
-bash-3.00$
```
0

ifconfig | grep HWaddr

phobot · 2011-04-26 15:34:56 3
Merge PDFs into single file
This is sample output - yours may be different.
0

pdftk input1.pdf input2.pdf cat output output.pdf

shanti · 2011-07-18 20:42:09 4
Prevent command history file from being overwritten by multiple shell sessions.

Takes effect immediately.
This is sample output - yours may be different.
0

echo "shopt -s histappend" >> ~/.bashrc ; . ~/.bashrc

dhart · 2011-11-03 09:57:18 3
cvs diff HEAD and current branch

you can't reliably use diff against -r HEAD to test whether a file matches the head of the trunk.
This is sample output - yours may be different.
0

cvs up -pA main.cpp | sdiff -s - main.cpp

kev · 2011-12-14 04:51:40 4
Print heap addresses and size

Show Sample Output
This is sample output - yours may be different.
```
b81db000-b81dc000 ---p 00000000 00:00 0          [heap]
Size:                  4 kB
Rss:                   0 kB
--
b81dc000-b81fb000 rw-p 00000000 00:00 0          [heap]
Size:                124 kB
Rss:                   4 kB
--
```
0

PID=`pgrep -o <process_name>`; grep -A 2 heap /proc/$PID/smaps

deimos · 2012-01-30 14:28:54 3
Create a file

Create empty file
This is sample output - yours may be different.
0

> filename

TIT · 2012-03-08 23:17:05 3
Create rsyncable tar archives with gzip compression
This is sample output - yours may be different.
0

GZIP="--rsyncable" tar -czf something.tgz /something

dash · 2012-04-24 19:06:56 4
Directory stack pushd popd dirs

manage directory stack Show Sample Output
This is sample output - yours may be different.
```
# cd /tmp/dir1
# pushd .
# cd /tmp/dir2
# pushd .
# cd /tmp/dir3
# pushd .
# cd /tmp/dir4
# pushd .
# dirs
/tmp/dir4 /tmp/dir4 /tmp/dir3 /tmp/dir2 /tmp/dir1
```
0

pushd path/to/dir/

ankush108 · 2012-06-26 17:23:55 6
Macports update and clean all packages
This is sample output - yours may be different.
0

sudo port selfupdate && sudo port upgrade outdated && sudo port clean --all installed && sudo port -f uninstall inactive

noah · 2013-06-26 01:12:33 10
execute/start some scripts on a remote machine/server (which will terminate automatically) and disconnect from the server

http://stackoverflow.com/questions/1628204/how-to-run-a-command-in-background-using-ssh-and-detach-the-session
This is sample output - yours may be different.
0

ssh remoteserver 'nohup /path/to/script `</dev/null` >nohup.out 2>&1 &'

prasad · 2013-11-30 09:38:13 7
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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"

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"

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"

List just the executable files (or directories) in current directory

A bit shorter ;)

Top Command in batch mode

running top command in batch mode. it is usefull if you want to redirect the output in a file.

find co-ordinates of a location

Just add this to your .bashrc file. Use quotes when query has multiple word length.

Backup entire system through SSH

check open ports without netstat or lsof

Image to color palette generator

Extract a color palette from a image useful for designers. Example usage: $extract-palette myawesomeimage.jpg 4 Where the first argument is the image you want to extract a palette from. The second argument is the number of colors you want. It may be the case where you want to change the search space. In that case, change the -resize argument to a bigger or smaller result. See the ImageMagick documentation for the -resize argument.

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