Tagged: commands

How to Flush DNS Cache in Mac OS X

- by admin

After upgrading to 10.8.2 I have got a problem with adding a new entry into hosts file: the update was recognised only after system restart. But a more easy solution was just to flash DNS cache! So,

... flushing your DNS cache in Mac OS X is actually really easy, and there are two different commands to use, one for Leopard and for Tiger. Depending on your version of OS X, open your Terminal and follow the appropriate directions below:

Flushing DNS Cache in OS X Lion (10.7) and OS X Mountain Lion (10.8)

Launch Terminal and enter the following command, you will need to enter an administrative password:
sudo killall -HUP mDNSResponder

Note the dscacheutil still exists in 10.7 and 10.8, but the official method to clear out DNS caches is through killing mDNSResponder. You can also find that process running in Activity Monitor.

Flush DNS Cache in Mac OS X 10.5, Mac OS X 10.6

Launch Terminal and issue the following command:
dscacheutil -flushcache

All done, your DNS has been flushed. On a side note, the dscacheutil is interesting in general and worth taking a look at, try the -statistics flag instead for some stats.

Flush your DNS Cache in Mac OS X 10.4 Tiger

Type the following command in the Terminal:
lookupd -flushcache

That’s it - now your DNS settings should be as you intended them to be :-)

Find (search) and replace text from command line in multiple files (Linu

- by admin

Another (and more easy) way to change text in multiple files is to use grep:
grep -lr -e 'oldtext' * | xargs sed -i 's/oldtext/newtext/g'

or to use PERL:
perl -p -i -e ’s/oldtext/newtext/g’ *


Find (search) and replace text from command line in multiple files (Linu

- by admin

Just after I posted this article the second more easy solution has been found. Here it is:

Find (search) and replace text from command line in multiple files (Linux) #2

When you are working on the Linux command line and you come across a large file or a large number of files in which you need to replace a certain text with another, finding and pasting over each instance of the text can be a bit time consuming. Well, worry no more. Linux has just the solution for you. Here’s a way to find and replace a string of text in one or more files automatically.

For the purpose of this exercise we will use a Linux command line tool called “sed”.  ”sed” is a very powerful and versatile tool, and a lot can be written about its capabilities. We are using a very limited aspect of “sed” here. I would definitely recommend that you read up a little more on “sed” if you find this aspect of it interesting.

We are going to use the following syntax to find and replace a string of text in a file:
# sed -i 's/[orginal_text]/[new_text]/' filename.txt

Say you have a file called “database.txt” with numerous instances of the IP address of your database server in it. You have just switched to a new database server and need to update it with the new server’s IP address. The old IP address is and the new one is Here’s how you go about it:
# cat database.txt
LOCAL_DIR = /home/calvin/

# sed -i 's/' database.txt
# cat database.txt
LOCAL_DIR = /home/calvin/

Now open the file “database.inc” and check to see if the new IP address has taken place of your old one. Here’s the breakup of the above command. First you call the “sed” command. Then you pass it the parameter “-s” which stands for “in place of”. Now we use a little bit of regular expressions, commonly known as “regex”  for the next bit. The “s” in the quoted string stands for “substitute”, and the “g” at the end stands for “global”. Between them they result in a “global substitution of the the string of text you place in between them.

You can optionally skip the “g” at the end. This means that the substitution will not be global, which practically translates to the substitution of only the first instance of the string in a line. So if you had a line with multiple instances of the text you are trying to replace, here’s what will happen
# cat database.txt
LOCAL_DIR = /home/calvin/

# sed -i 's/' database.txt
# cat database.txt
LOCAL_DIR = /home/calvin/

Here comes the real magic. Now, say you want to change a string of text not just in a single file, but in the entire directory you are in. There are a number of text files in which you need to find and replace the “wine” with “champagne”.
# find . -maxdepth 1 -name "*.txt" -type f -exec sed -i 's/wine/champagne/' {} \

We use the find command to get a list of all the text files in the current directory. That’s the “find . -maxdepth 1 -name “*.txt” -type f” part. “find . maxdepth 1″ tell the computer to look in the current directory and go no deeper than the current directory. The ‘-name  ”*.txt”‘ part tells find to only list files with the extension of “.txt”. Then the “-type f” section specifies that “find” should only pick exactly matching files. Finally the “-exec” part tells “find” to execute the command that follows, which, in this case, is the “sed” command to replace the text – “sed -i ‘s/wine/champagne/’ {} \”.

I realize that the above command seems complicated. However, once you use it a little bit you will realize that it is probably worth noting it down and using it. Now try changing a string of text in multiple levels of directories.

Git Cheat Sheet

- by admin


identify yourself to git: email and your name

git config --global user.name "John Smith"

git config --global user.email "abc@mail.com"

To view all options:

git config --list


cat .git/config

Set up aliases

git config --global alias.co checkout

View your configuration

cat .gitconfig

To ignore whitespace (Ruby is whitespace insensitive)

git config --global apply.whitespace nowarn

Some nice aliases:

gb = git branch
gba = git branch -a
gc = git commit -v
gd = git diff | mate
gl = git pull
gp = git push
gst = git status

Start using git

git init

Ignoring files

Add a file in the root directory called .gitignore and add some files to it: (comments begin with hash)

*.log db/schema.rb db/schema.sql

Git automatically ignores empty directories. If you want to have a log/ directory, but want to ignore all the files in it, add the following lines to the root .gitignore: (lines beginning with ‘!’ are exceptions)


Then add an empty .gitignore in the empty directory:

touch log/.gitignore

Scheduling the addition of all files to the next commit

git add .

Checking the status of your repository

git status

Committing files

git commit -m "First import"

Seeing what files have been committed

git ls-files

Scheduling deletion of a file

git rm [file name]

Committing all changes in a repository

git commit -a

Scheduling the addition of an individual file to the next commit

git add [file name]

Viewing the difference as you commit

git commit -v

Commit and type the message on the command line

git commit -m "This is the message describing the commit"

Commit and automatically get any other changes

git commit -a

A “normal” commit command

git commit -a -v

Viewing a log of your commits

git log

Viewing a log of your commits with a graph to show the changes

git log --stat

Viewing a log with pagination

git log -v

Visualizing git changes

gitk --all

Creating a new tag and pushing it to the remote branch

git tag "v1.3"
git push --tags

Creating a new branch

git branch [name of your new branch]

Pushing the branch to a remote repository

git push origin [new-remote]

Pulling a new branch from a remote repository

git fetch origin [remote-branch]:[new-local-branch]

Viewing branches

git branch

Viewing a list of all existing branches

git branch -a

Switching to another branch

The state of your file system will change after executing this command.

git checkout [name of the branch you want to switch to]


git co [name of the branch you want to switch to]

Making sure changes on master appear in your branch

git rebase master

Merging a branch back into the master branch

First, switch back to the master branch:

git co master

Check to see what changes you’re about to merge together, compare the two branches:

git diff master xyz

If you’re in a branch that’s not the xyz branch and want to merge the xyz branch into it:

git merge xyz

Reverting changes to before said merge

git reset --hard ORIG_HEAD

Resolving conflicts

Remove the markings, add the file, then commit.

Creating a branch (and switching to the new branch) in one line

git checkout -b [name of new branch]

Creating a stash (like a clipboard) of changes to allow you to switch branches without committing

git stash save "Put a message here to remind you of what you're saving to the clipboard"

Switching from the current branch to another

git co [branch you want to switch to]

Do whatever
Then switch back to the stashed branch

git co [the stashed branch]

Viewing a list of stashes

git stash list

Loading back the stash

git stash apply

Now you can continue to work where you were previously.

Deleting a branch (that has been merged back at some point)

git branch -d [name of branch you want to delete]

Deleting an unmerged branch

git branch -D [name of branch you want to delete]

Deleting a stash

git stash clear

Setting up a repository for use on a remote server

Copy up your repository. e.g.:

scp -r my_project deploy@yourbox.com:my_project

Move your files on the remote server to /var/git/my_project
For security make the owner of this project git
On the repository server:

sudo chown -R git:git my_project

Then (for security) restrict the “deploy” user to doing git-related things in /etc/passwd with a git-shell.

Checking out a git repository from a remote to your local storage

git clone git@yourbox.com:/var/git/my_project

Viewing extra info about a remote repository

cat .git/config

By virtue of having cloned the remote repository, your local repository becomes the slave and will track and synchronize with the remote master branch.

Updating a local branch from the remote server

git pull

Downloading a copy of an entire repository (e.g. laptop) without merging into your local branch

git fetch laptop

Merging two local branches (ie. your local xyz branch with your local master branch)USE MERGE

git merge laptop/xyz

This merged the (already copied laptop repository’s xyz branch) with the current branch you’re sitting in.

Viewing metadata about a remote repository

git remote show laptop

Pushing a committed local change from one local branch to another remote branch

git push laptop xyz

Creating a tracking branch (i.e. to link a local branch to a remote branch)

git branch --track local_branch remote_branch

You do not need to specify the local branch if you are already sitting in it.

git pull

Note: You can track(link) different local branches to different remote machines. For example, you can track your friend’s “upgrade” branch with your “bobs_upgrade” branch, and simultaneously you can track the origin’s “master” branch (of your main webserver) with your local “master” branch.

By convention, ‘origin’ is the local name given to the remote centralized server which is the waySVN is usually set up on a remote server.

Seeing which local branches are tracking a remote branch

git remote show origin

Working with a remote Subversion repository (but with git locally)

git-svn clone [http location of an svn repository]

Now you can work with the checked out directory as though it was a git repository. (cuz it is)

Pushing (committing) changes to a remote Subversion repository

git-svn dcommit

Updating a local git repository from a remote Subversion repository

git-svn rebase

NOTE: make sure you have your perl bindings to your local svn installation.

I screwed up, how do I reset my checkout?

git checkout -f

VIM Editor Commands

- by admin

Vim is an editor to create or edit a text file.

There are two modes in vim. One is the command mode and another is the insert mode.
In the command mode, user can move around the file, delete text, etc.
In the insert mode, user can insert text.

Changing mode from one to another

From command mode to insert mode type a/A/i/I/o/O ( see details below)
From insert mode to command mode type Esc (escape key)

Some useful commands for VIM

Text Entry Commands (Used to start text entry)

a Append text following current cursor position
A Append text to the end of current line
i Insert text before the current cursor position
I Insert text at the beginning of the cursor line
o Open up a new line following the current line and add text there
O Open up a new line in front of the current line and add text there
The following commands are used only in the commands mode.

Cursor Movement Commands

h Moves the cursor one character to the left
l Moves the cursor one character to the right
k Moves the cursor up one line
j Moves the cursor down one line
nG or :n Cursor goes to the specified (n) line
(ex. 10G goes to line 10)
^F (CTRl F) Forward screenful
^B Backward screenful
^f One page forward
^b One page backward
^U Up half screenful
^D Down half screenful
$ Move cursor to the end of current line
0 (zero) Move cursor to the beginning of current line
w Forward one word
b Backward one word
Exit Commands
:wq Write file to disk and quit the editor
:q! Quit (no warning)
:q Quit (a warning is printed if a modified file has not been saved)
ZZ Save workspace and quit the editor (same as :wq)
: 10,25 w temp
write lines 10 through 25 into file named temp. Of course, other line
numbers can be used. (Use :f to find out the line numbers you want.

Text Deletion Commands

x Delete character
dw Delete word from cursor on
db Delete word backward
dd Delete line
d$ Delete to end of line
d^ (d caret, not CTRL d) Delete to beginning of line
Yank (has most of the options of delete)-- VI's copy commmand
yy yank current line
y$ yank to end of current line from cursor
yw yank from cursor to end of current word
5yy yank, for example, 5 lines
Paste (used after delete or yank to recover lines.)
p paste below cursor
P paste above cursor
"2p paste from buffer 2 (there are 9)
u Undo last change
U Restore line
J Join next line down to the end of the current line

File Manipulation Commands

:w Write workspace to original file
:w file Write workspace to named file
:e file Start editing a new file
:r file Read contents of a file to the workspace
To create a page break, while in the insert mode, press the CTRL key
And l. ^L will appear in your text and will cause the printer to start
A new page.

Other Useful Commands

Most commands can be repeated n times by typing a number, n, before
the command. For example 10dd means delete 10 lines.
. Repeat last command
cw Change current word to a new word
r Replace one character at the cursor position
R Begin overstrike or replace mode – use ESC key to exit
:/ pattern Search forward for the pattern
:? pattern Search backward for the pattern
n (used after either of the 2 search commands above to
continue to find next occurrence of the pattern.
:g/pat1/s//pat2/g replace every occurrence of pattern1 (pat1) with pat2
Example :g/tIO/s//Ada.Text_IO/g
This will find and replace tIO by Ada.text_IO everywhere in the file.
:g/a/s// /g replace the letter a, by blank
:g/a/s///g replace a by nothing
note: Even this command be undone by u


Opening a New File

Step 1 type vim filename (create a file named filename)
Step 2 type i ( switch to insert mode)
Step 3 enter text (enter your Ada program)
Step 4 hit Esc key (switch back to command mode)
Step 5 type :wq (write file and exit vim)

Editing the Existing File

Step 1 type vim filename (edit the existing file named filename)
Step 2 move around the file using h/j/k/l key or any appropriate command
h Moves the cursor one character to the left
l Moves the cursor one character to the right
k Moves the cursor up one line
j Moves the cursor down one line
nG or :n Cursor goes to the specified (n) line
(ex. 10G goes to line 10)
Step 3 edit required text (replace or delete or insert)
Step 4 hit Esc key (exit from insert mode if you insert or replace text)
Step 5 type :wq

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