Category Archives: technical

vimdiff ignore white space

To ignore white spaces while using vimdiff.

set diffopt+=iwhite

From the command line use:

vimdiff -c 'set diffopt+=iwhite' ...

To have vimdiff ignore whitespace while normal vim doesn’t, simply put this into your .vimrc:

if &diff
    " diff mode"
    set diffopt+=iwhite

CURL usage

There are some powerful features of curl you did not know before

Used curl to grab all headers with ‘-H’

$ curl -I ""
HTTP/1.1 200 OK
X-Powered-By: PHP/5.5.1
Content-Type: text/html; charset=UTF-8
Date: Mon, 24 Mar 2014 02:04:01 GMT
Server: lighttpd/1.4.34

Send a header to web server with ‘-H’

  • The curl command supports -H or –header option to pass extra HTTP header to use when getting a web page from a web server.
  • This option can be used multiple times to add/replace/remove multiple headers, the syntax is:

curl -H 'HEADER-1' -H 'HEADER-2' ... <URL>

E.g Check if apache node is working or not

curl -I -H 'Host:' ''

Checking gzip/deflate server responses with curl

Curl provides a simple tool for checking server responses.

First, a few curl arguments that will come in handy:

-s, --silent prevents curl from showing progress meter

-w, --write-out 'size_download=%{size_download}\n' instructs curl to print out the download size

-o, --output instructs curl to throw away the output, sending it to /dev/null

Using these arguments, we can make a simple request for a path on the server:

curl -s -w "size_download=%{size_download}\n" -o /dev/null \

Here, you can the response was 83615 bytes. Next up, lets make the same
request, this time adding the Accept-Encoding header to ask for compressed

curl -s -w "size_download=%{size_download}\n" -o /dev/null \
     -H "Accept-Encoding: gzip,deflate" \

Nice! This downloaded only 34151 bytes of data, so it the data is definitely
being compressed. Up next, lets try making the request a third time, now
making the request a HTTP1.0 request.

curl -s -w "size_download=%{size_download}\n" -o /dev/null \
     -H "Accept-Encoding: gzip,deflate" \

This time, response same as first request, which makes sense when using Nginx
with the [gzip_http_version](
tp_version) set to 1.1.

Specify the user name and password to use for server authentication

Reference from manual

-u, –user

Specify the user name and password to use for server authentication. Overrides -n,
–netrc and –netrc-optional.

If you simply specify the user name, curl will prompt for a password.

The user name and passwords are split up on the first colon, which makes it
impossible to use a colon in the user name with this option. The password can, still.

curl -u allex:d9e871f ""


Uses for ~/.ssh/config

For system and network administrators or other users who frequently deal with sessions on multiple machines, SSH ends up being one of the most oft-used Unix tools. SSH usually works so well that until you use it for something slightly more complex than starting a terminal session on a remote machine, you tend to use it fairly automatically. However, the ~/.ssh/config file bears mentioning for a few ways it can make using the ssh a client a little easier.

Abbreviating hostnames

If you often have to SSH into a machine with a long host and/or network name,
it can get irritating to type it every time. For example, consider the
following command:

$ ssh

If you interact with the iallex machine a lot, you could include a stanza
like this in your ~/.ssh/config:

Host iallex

This would allow you to just type the following for the same result: ssh web0911, Of course, if you have root access on the system, you could also do this by adding the hostname to your /etc/hosts file, or by adding the domain to your /etc/resolv.conf to search it, but I prefer the above solution as it’s cleaner and doesn’t apply system-wide.

Fixing alternative ports

If any of the hosts with which you interact have SSH processes listening on alternative ports, it can be a pain to both remember the port number and to type it in every time:

$ ssh -p 5331

You can affix this port permanently into your .ssh/config file instead:

    Port 5331

This will allow you to leave out the port definition when you call ssh on that host: ssh

Custom identity files

If you have a private/public key setup working between your client machine and the server, but for whatever reason you need to use a different key from your normal one, you’ll be using the -i flag to specify the key pair that should be used for the connection:

$ ssh -i ~/.ssh/id_dsa.stage srv1.stage

You can specify a fixed identity file in .ssh/config just for these hosts instead, using an asterisk to match everything in that domain:

Host *.stage
    IdentityFile ~/.ssh/id_dsa.stage

I need to do this for Mikrotik’s RouterOS connections, as my own private key structure is 2048-bit RSA which RouterOS doesn’t support, so I keep a DSA key as well just for that purpose.

Force SSH client to use password authentication instead of public key

ssh -o PubkeyAuthentication=no apps@fe-dev-142

Also a shortcut for this purpose:
ssh user:@fe-dev-142

Note the colon (:) and the empty password after it.

Logging in as a different user

By default, if you omit a username, SSH assumes the username on the remote machine is the same as the local one, so for servers on which I’m called tom, I can just type:

ssh # => ssh

However, on some machines I might be known as a different username, and hence need to remember to connect with one of the following:

ssh -l jack
# or

If I always connect as the same user, it makes sense to put that into my .ssh/config instead, so I can leave it out of the command entirely:

    User jack

SSH proxies

If you have an SSH server that’s only accessible to you via an SSH session on an intermediate machine, which is a very common situation when dealing with remote networks using private RFC1918 addresses through network address translation, you can automate that in .ssh/config too. Say you can’t reach the host nathost directly, but you can reach some other SSH server on the same private subnet that is publically accessible,

Host nathost
    ProxyCommand ssh -q -W %h:%p

This will allow you to just type: ssh nathost

More information

The above are the .ssh/config settings most useful to me, but there are plenty more available; check man ssh_config for a complete list.

Git Basics: diff commit and merge branches


Use git diff show the difference between commits.

git co master
git diff 0da94be..59ff30c > /tmp/my.patch
# Checkout new branch: (this will not reset your work)
git co branches-dev git apply /tmp/my.patch

Diff a single file by different commits:

git diff 5bb72a8 HEAD -- twentytwelve/style.cs

Compare files from two different branches:

# You can do this: `git diff branch1:file branch2:file`
git diff master:twentytwelve/style.css branche-dev:twentytwelve/style.css

Git – Create a branch with current changes

Just use:

git checkout -b topic/newbranch

Any uncommitted work will be taken along to the new branch.

GIT Merge

Merge some (not all) files from one Git branch to another.

As it turns out, we’re trying too hard. Our good friend git checkout is the right tool for the job.

git checkout <branch> <paths>...

We can simply give git checkout the name of the feature branch and the paths to the specific files that we want to add to our master branch.

# merge a single commit from another branch
git cherry-pick <commit_sha1>

# merge without auto commit
git merge v1.0 --no-commit --no-ff

Syncing a fork

Merge the changes from upstream/master into your local master branch. This brings your fork’s master branch into sync with the upstream repository, without losing your local changes.
We can configure git to sync your fork with the original repository git remote add upstream <ORIGINAL_REPOSITORY.git>

git merge upstream/master
# Updating a422352..5fdff0f
# Fast-forward
#  README                    |    9 -------
#                 |    7 ++++++
#  2 files changed, 7 insertions(+), 9 deletions(-)
#  delete mode 100644 README
#  create mode 100644

Git merge “accept theirs” or “accept mine” options

git checkout --ours -- <filename>
git checkout --theirs -- <filename>

Resolving the conflict

Just modify the files conflicting. You would need to call git add to mark the conflict as resolved:

$ git add file_with_resolved_conflicts

This will also add the file to the index. After you repeat the same process for other conflicting files, you can safely commit your changes using git commit command:

git commit -m 'Merged with branch src-branch and resolved the conflicts.'


Helper commands

  • use git difftool to manally merge files: git config merge.tool vimdiff
  • undo current changess: git reset --hard origin/master

Reference Links

Adding And Removing Remote Branches – Git Branch

Nginx – confusion with root & alias


There is a very important difference between the root and the alias directives.
This difference exists in the way the path specified in the root or the alias is processed.

In case of the root directive, full path is appended to the root including the location part, whereas in case of the alias directive, only the portion of the path NOT including the location part is appended to the alias.


Let’s say we have the config

location /static/ {
    root /var/www/app/static/;
    autoindex off;

In this case the final path that Nginx will derive will be:


This is going to return 404 since there is no static/ within static/

This is because the location part is appended to the path specified in the root. Hence, with root, the correct way is:

location /static/ {
    root /var/www/app/;
    autoindex off;

On the other hand, with alias, the location part gets dropped. So for the config:

location /static/ {
    alias /var/www/app/static/;
    autoindex off;

the final path will correctly be formed as:


See the documentation here:

git squashing commits with rebase

git rebase – Forward-port local commits to the updated upstream head

We can use git rebase --interactive (or -i) mode to squash multiple snapit commit.

git rebase -i HEAD~2
pick b76d157 b
pick a931ac7 c

Changing b’s pick to squash will result in the error you saw, but if instead you squash c into b by changing the text to:

pick b76d157 b
s a931ac7 c

For more details reference:

Apache prevent web browsers from caching

In order to get the latest effections, Front-end develop need to refresh the web page frequently.

there some solution for fix page cache problem:

Ensure the request url is unique.

by adding random seed to URL. such as

<script src="${version}"></script>

But this case need some server programe to generic the html page resouces references dynamic.

The other one and the more simple way is prevent Web browsers by customize HTTP Headers.

Setting a short cache time

By asking the Web browser to only cache the file for a very short length of time, you can usually avoid the problem.

We support the Apache Web server “mod_expires” feature. To use this to set the cache time to just one second, add these lines to a .htaccess file:

ExpiresActive On
ExpiresDefault A1
Header append Cache-Control must-revalidate

That’s all it takes. The next time the visitor views the file, more than a second will have passed, so the browser won’t use the outdated cached copy.

Controlling which files are affected

Disabling browser caching will slow down your site and increase the amount of bandwidth your site uses, because repeat visitors will always connect to your site to re-download files they would otherwise cache.

To minimize that impact, you might want to prevent caching of files that change often (such as HTML files), while allowing normal caching of files that don’t (such as JPEG files).

To do this, include the .htaccess lines in a <FilesMatch> directive. For example, these lines will prevent caching of filenames ending in “.htm” or “.html”, while allowing normal caching of JPEG files:

<FilesMatch "\.(htm|html|js|css)$">
  ExpiresActive On
  ExpiresDefault A1
  Header append Cache-Control must-revalidate

(An alternate way of doing this is to use the Apache “ExpiresByType text/html” command, but that doesn’t allow you to add the “Cache-Control: must-revalidate” header for only those pages.)

For more info about Apache headers see also: Manipulating HTTP Headers with htaccess.