Snippets

Contents

  1. Linux
    1. Create *nix timestamp
    2. Convert screencast video
    3. bash/zsh use cursor up/down keys for command history up/down
    4. TrueCrypt GUIless/console mount encrypted volume
    5. Find out which application runs on a given port and protocol
    6. List your hardware
    7. Directory tree comparison
    8. Backup directory using rsync with progress bar
    9. Tell SVN not to store your password in .svn ..
    10. Execute function on shell script exit
    11. Curl send header
    12. Curl send POST request
    13. Curl get all response headers
  2. SQL
    1. Partially anonymize e-mail addresses
    2. Find duplicate entries
    3. Postgres create roles
    4. Postgres set user password
    5. Postgres change database
  3. Java
    1. Show processes
    2. Create heap dump from running process
    3. Create heap dump on OutOfMemoryError
    4. Screen detach session/ list  / reattach
  4. Apache Webserver
    1. Deny all methods excepting POST and GET
    2. Rewrite all aliases for a domain to a single domain
 

A collection of snippets I’m using sometimes but my brain refuses to remember ..

Linux

Create *nix timestamp

 
date --utc --date "2011-11-11 11:11:11" +%s

Convert screencast video

 
mencoder -idx input.ogv -ovc lavc -oac mp3lame -o output

bash/zsh use cursor up/down keys for command history up/down

 
bindkey "^[[A" history-search-backward
bindkey "^[[B" history-search-forward

TrueCrypt GUIless/console mount encrypted volume

 
sudo truecrypt -t -k "" --protect-hidden=no /path/to/encfile /path/to/mountpoint

Find out which application runs on a given port and protocol

 
sudo fuser -n tcp 8080

List your hardware

 
sudo lshw

Directory tree comparison

 
diff -r dir1 dir2

Backup directory using rsync with progress bar

 
rsync -h --progress --stats -r -tgo -l -p -D --update --delete-after /path/to/dir-to-be-saved /path/to/targetdir/

Tell SVN not to store your password in .svn ..

 
svn command --no-auth-cache

Execute function on shell script exit

 
#!/bin/sh
# exit function
onExit() {
   # do something here .. cleanup etc ....
}
# bind exit function
trap onExit ERR EXIT
 
# here's the normal code to be executed

Curl send header

 
curl -H "headername:value" url
 
e.g. curl -H "REMOTE_USER:foo" http://developers.android.com

Curl send POST request

 
curl -X POST url
 
e.g. curl -X POST http://developers.android.com

Curl get all response headers

 
curl -i url
 
e.g. curl -i http://developers.android.com

SQL

Partially anonymize e-mail addresses

 
UPDATE <TABLE_NAME>
SET <EMAIL_FIELD>=
  INSERT(
    <EMAIL_FIELD>,
    POSITION('@' IN <EMAIL_FIELD>),
    100,
    CONCAT(FLOOR(1 + (RAND() * 100)),'@hascode.com'))
  WHERE
    POSITION('@' IN <EMAIL_FIELD>)>0;

Find duplicate entries

 
SELECT COUNT(*), <FIELDNAME> FROM <TABLENAME>
GROUP BY <FIELDNAME>
HAVING COUNT(*)>1;

Postgres create roles

 
CREATE ROLE name;
DROP ROLE name;
SELECT rolname FROM pg_roles;
\du
GRANT name TO username

Postgres set user password

 
ALTER USER
ALTER USER root WITH password 'xxx';

Postgres change database

 
\cDBNAME

Java

Show processes

 
jps

Create heap dump from running process

 
jmap -dump:format=b,file=/tmp/heap.bin 2381

Create heap dump on OutOfMemoryError

 
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/path/to/save/dumps

Screen detach session/ list  / reattach

Detach: Ctrl + A + D

List: 

$ screen -ls
There is a screen on:
    2859.pts-0.host    (11/07/11 20:18:00)    (Detached)
1 Socket in /var/run/screen/S-user.

Reattach:

screen -r 2859.pts-0.host

Apache Webserver

Deny all methods excepting POST and GET

 

RewriteCond %{REQUEST_METHOD} ^(TRACE|TRACK|OPTIONS|HEAD)
RewriteRule .* - [F]

Rewrite all aliases for a domain to a single domain

 
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www\.)?mydomain1\.com [NC,OR]
RewriteCond %{HTTP_HOST} ^(www\.)?mydomain2\.com [NC,OR]
RewriteCond %{HTTP_HOST} ^(www\.)?mydomain3\.com [NC,OR]
RewriteRule (.*) http://mydomain.com/$1 [R=301,L]
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