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Execute a command before display the bash prompt

For example, if you are the type who type ls very often, then PROMPT_COMMAND=ls will ls after every command you issue.
This is sample output - yours may be different.
1

PROMPT_COMMAND=command

haivu · 2009-10-15 06:01:18 3
Outputs a 10-digit random number
This is sample output - yours may be different.
-2

n=$RANDOM$RANDOM$RANDOM; let "n %= 10000000000"; echo $n

alset · 2009-10-15 05:10:00 4
GZip all files in a directory separately
This is sample output - yours may be different.
2

gzip *

haplo · 2009-10-15 03:28:22 6
GZip all files in a directory separately
This is sample output - yours may be different.
1

ls | xargs -n1 gzip

haplo · 2009-10-15 03:10:38 3
GZip all files in a directory separately

It gzip each file in a directory separately
This is sample output - yours may be different.
1

for file in *.foo; do gzip "$file"; done

dfrios · 2009-10-15 01:27:05 3
Command to resolve name from Ip address, passing only the last field after seq (C Class for example)

Show Sample Output
This is sample output - yours may be different.
```
164.85.216.1 - station1.domain.biz
164.85.216.2 - station2.domain.biz
164.85.216.3 - station3.domain.biz
164.85.216.4 - station4.domain.biz
```
0

seq 4|xargs -n1 -i bash -c "echo -n 164.85.216.{} - ; nslookup 164.85.216.{} |grep name"|tr -s ' ' ' '|awk '{print $1" - "$5}'|sed 's/.$//'

Waldirio · 2009-10-14 19:57:24 3
Get absolut path to your bash-script

Another way of doing it that's a bit clearer. I'm a fan of readable code.
This is sample output - yours may be different.
7

script_path=$(cd $(dirname $0);pwd)

jgc · 2009-10-14 16:04:03 8
MoscowML with editable input-line and history

Works also with SML/NJ and other interpreters or tools with interactive environments.
This is sample output - yours may be different.
1

rlwrap mosml

hons · 2009-10-14 07:39:10 8
validate the syntax of a perl-compatible regular expression

Place the regular expression you want to validate between the forward slashes in the eval block. Show Sample Output
This is sample output - yours may be different.
```
$ perl -we 'my $regex = eval {qr/*/}; die "$@" if $@;'
Quantifier follows nothing in regex; marked by <-- HERE in m/* <-- HERE / at -e line 1.
```
5

perl -we 'my $regex = eval {qr/.*/}; die "$@" if $@;'

tlacuache · 2009-10-13 21:50:47 10
Display the history and optionally grep

Place this in your .bash_profile and you can use it two different ways. If you issue 'h' on its own, then it acts like the history command. If you issue: h cd Then it will display all the history with the word 'cd'
This is sample output - yours may be different.
7

h() { if [ -z "$1" ]; then history; else history | grep "$@"; fi; }

haivu · 2009-10-13 21:49:37 10
retrieve the source address used to contact a given host

on multihomed hosts, connected to several networks, could be usefull to know the source address (local ip address) used to reach the target host, this command does not require root priviledges. The command use a TCP socket, if there is any error the command return an empty string, elsewhere return a valid ip address. Show Sample Output
This is sample output - yours may be different.
```
$ python -c 'import socket;  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM); s.connect(("www.google.com", 80)); print s.getsockname()[0] ; s.close() ;' 2> /dev/null
192.168.26.198
```
2

python -c 'import socket; s = socket.socket(socket.AF_INET, socket.SOCK_STREAM); s.connect(("<hostname>", <port>)); print s.getsockname()[0] ; s.close() ;' 2> /dev/null

angleto · 2009-10-13 16:21:15 3
Get absolut path to your bash-script
This is sample output - yours may be different.
4

PATH=$(cd ${0%/*}; pwd)

hons · 2009-10-13 16:02:31 5
Check a server is up. If it isn't mail me.

Joker wants an email if the Brand X server is down. Set a cron job for every 5 mins with this line and he gets an email when/if a ping takes longer than 3 seconds. Show Sample Output
This is sample output - yours may be different.
```
An email saying "brandx.jp.sme ping failed"
```
8

ping -q -c1 -w3 brandx.jp.sme 2&>1 /dev/null || echo brandx.jp.sme ping failed | mail -ne -s'Server unavailable' joker@jp.co.uk

mccalni · 2009-10-13 14:13:04 19
Start xterm in given directory

Perfect time for the rarely used sub shell.
This is sample output - yours may be different.
-4

( cd /my/directory; xterm& )

ashawley · 2009-10-13 13:07:21 5
Start xterm in given directory

Usefull e.g. in krusader open terminal function
This is sample output - yours may be different.
-4

xterm -e "cd /my/directory; bash"

kekschaot · 2009-10-13 12:06:14 7
Perform sed substitution on all but the last line of input

In this simple example the command will add a comma to the end of every line except the last. I found this really useful when programatically constructing sql scripts. See sample output for example. Show Sample Output
This is sample output - yours may be different.
```
$ cat myfile.txt
cola
colb
colc
$ sed -e "$ ! s/$/,/" myfile.txt
cola,
colb,
colc
```
5

sed -e "$ ! s/$/,/"

jgc · 2009-10-13 10:13:52 7
Outputs a 10-digit random number
This is sample output - yours may be different.
0

echo $RANDOM$RANDOM$RANDOM |cut -c3-12

emmerich164 · 2009-10-13 08:08:45 4
Get full URL via http://untr.im/api/ajax/api

Get full url via untr.im Show Sample Output
This is sample output - yours may be different.
```
http://socialmedia.globalthoughtz.com/index.php/facebook-database-outage-cut-off-about-150-thousand/
```
1

URL=[target.URL]; curl -q -d "url=$URL" http://untr.im/api/ajax/api | awk -F 'href="' '{print $3}' | awk -F '" rel="' '{print $1}'

ad · 2009-10-13 03:49:26 3
remove the last of all html files in a directory

plays with bash arrays. instead of storing the list of files in a temp file, this stores the list in ram, retrieves the last element in the array (the last html file), then removes it.
This is sample output - yours may be different.
-3

a=($(ls *html)) && a=${a[$(expr ${#a[@]} - 1)]} && rm $a

linuxrawkstar · 2009-10-12 16:40:06 5
convert vdi to vmdk (virtualbox hard disk conversion to vmware hard disk format)

Converts a .vdi file to a .vmdk file for use in a vmware virtual machine. The benefit: using this method actually works. There are others out there that claim to give you a working .vmdk by simply using the qemu-img command alone. Doing that only results in pain for you because the .vmdk file will be created with no errors, but it won't boot either. Be advised that these conversions are very disk-intensive by nature; you are probably dealing with disk images several gigabytes in size. Once finished, the process of using the new .vmdk file is left as an exercise to the reader. Show Sample Output
This is sample output - yours may be different.
```
VirtualBox Command Line Management Interface Version 2.2.4
(C) 2005-2009 Sun Microsystems, Inc.
All rights reserved.

Converting image "winxp.vdi" with size 32212254720 bytes (30720MB) to raw...

(VMDK) image open: flags=0x2 filename=winxp.vmdk
```
10

VBoxManage internalcommands converttoraw winxp.vdi winxp.raw && qemu-img convert -O vmdk winxp.raw winxp.vmdk && rm winxp.raw

linuxrawkstar · 2009-10-12 16:23:37 5

Calculates the size on disk for each package installed on the filesystem (or removed but not purged). This is missing the | sort -rn which would put the biggest packges on top. That was purposely left out as the command is slightly on the slow side Also you may need to run this as root as some files can only be checked by du if you can read them ;) Show Sample Output

This is sample output - yours may be different.

176     acl                                                                                                                                     
44      acpi                                                                                                                                    
396     acpi-support                                                                                                                            
32      acpi-support-base                                                                                                                       
108     acpid                                                                                                                                   
524     adduser                                                                                                                                 
408     akonadi-server                                                                                                                          
2416    akregator                                                                                                                               
388     alsa-base                                                                                                                               
1840    alsa-utils                                                                                                                              
1860    amor                                                                                                                                    
96      anacron                                                                                                                                 
120     apmd                                                                                                                                    
4512    apt                                                                                                                                     
104     apt-file                                                                                                                                
376     apt-utils                                                                                                                               
140     apt-xapian-index                                                                                                                        
9184    aptitude                                                                                                                                
112     at                                                                                                                                      
104     avahi-autoipd                                                                                                                           
252     avahi-daemon                                                                                                                            
260     base-files                                                                                                                              
100     base-passwd                                                                                                                             
du: cannot access `diverted by dash to: /usr/share/man/man1/sh.distrib.1.gz': No such file or directory                                         
du: cannot access `diverted by dash to: /bin/sh.distrib': No such file or directory

dpkg --get-selections | cut -f1 | while read pkg; do dpkg -L $pkg | xargs -I'{}' bash -c 'if [ ! -d "{}" ]; then echo "{}"; fi' | tr '\n' '\000' | du -c --files0-from - | tail -1 | sed "s/total/$pkg/"; done

pykler · 2009-10-12 14:57:54 5

remove the last of all html files in a directory

sed can be used deleting the last line and with -i option, there's no need to for temp files, the change is made on the actual file
This is sample output - yours may be different.
1

for f in *.html; do sed '$d' -i "$f"; done

alperyilmaz · 2009-10-12 14:46:43 4
remove the last line of all html files in a directory

Some malicious program appends a iframe or script tag to you web pages on some server, use this command to clean them in batch.
This is sample output - yours may be different.
-1

for f in *.html; do head -n -1 $f > temp; cat temp > $f; rm temp; done

Sunng · 2009-10-12 12:49:18 5
Makefile argument passing

This would allow reference of $(VAR) (if defined) with the value 'foobar' within the Makefile.
This is sample output - yours may be different.
1

make [target] VAR=foobar

cifr · 2009-10-12 09:42:30 3
Stop long commands wrapping around and over-writing itself in the Bash shell

add the command either in /etc/profile or ~/.bash_profile so that this is available to your shell. Show Sample Output
This is sample output - yours may be different.
```
type a reasonably long command, such as something simple like this: echo "an exceedingly long command that's much longer than the current window size. Something that you know will wrap around". to see the over-write.
```
3

shopt -s checkwinsize

settermjd · 2009-10-12 07:08:55 14
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gh or "grep history" - define a function gh combining history and grep to save typing

By defining a function "gh" as shown here, it saves me typing "history | grep" every time I need to search my shell history because now I only have to type "gh". A nifty time saver :-) You can also add the "gh" function definition to your .bashrc so it is defined each time you login. (updated 2015_01_29: changed from hg to gh to avoid clash with that other hg command. mnemonic: gh = grep history)

list all opened ports on host

remove leading blank lines

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

Creates a symbolic link or overwrites an existing one

-n: dereference the existing link -v: (optional) to be sure of what is being done -f: force the deletion of the existing one -s: creates a symlink Be careful: the destination can also be a file or a directory and it will be overwritten.

find the difference between two nodes

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"

Find usb device in realtime

Using this command you can track a moment when usb device was attached.

tail: watch a filelog

-f file(s) to be monitorized -n number of last line to be printed on the screen in this example, the content of two files are displayed

Put the machine to sleep after the download(wget) is done

[Note: This command needs to be run as root]. If you are downloading something large at night, you can start wget as a normal user and issue the above command as root. When the download is done, the computer will automatically go to sleep. If at any time you feel the computer should not go to sleep automatically(like if you find the download still continuing in the morning), just create an empty file called nosleep in /tmp directory.

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