Bash Shortcuts For Maximum Productivity

http://www.skorks.com/2009/09/bash-shortcuts-for-maximum-productivity/

It may or may not surprise you to know that the bash shell has a very rich array of convenient shortcuts that can make your life, working with the command line, a whole lot easier. This ability to edit the command line using shortcuts is provided by the GNU Readline library. This library is used by many other nix application besides bash, so learning some of these shortcuts will not only allow you to zip around bash commands with absurd ease :), but can also make you more proficient in using a variety of other nix applications that use Readline. I don’t want to get into Readline too deeply so I’ll just mention one more thing. By default Readline uses emacs key bindings, although it can be configured to use the vi editing mode, I however prefer to learn the default behavior of most applications (I find it makes my life easier not having to constantly customize stuff). If you’re familiar with emacs then many of these shortcuts will not be new to you, so these are mostly for the rest of us :).

Command Editing Shortcuts

Ctrl + a – go to the start of the command line
Ctrl + e – go to the end of the command line
Ctrl + k – delete from cursor to the end of the command line
Ctrl + u – delete from cursor to the start of the command line
Ctrl + w – delete from cursor to start of word (i.e. delete backwards one word)
Ctrl + y – paste word or text that was cut using one of the deletion shortcuts (such as the one above) after the cursor
Ctrl + xx – move between start of command line and current cursor position (and back again)
Alt + b – move backward one word (or go to start of word the cursor is currently on)
Alt + f – move forward one word (or go to end of word the cursor is currently on)
Alt + d – delete to end of word starting at cursor (whole word if cursor is at the beginning of word)
Alt + c – capitalize to end of word starting at cursor (whole word if cursor is at the beginning of word)
Alt + u – make uppercase from cursor to end of word
Alt + l – make lowercase from cursor to end of word
Alt + t – swap current word with previous
Ctrl + f – move forward one character
Ctrl + b – move backward one character
Ctrl + d – delete character under the cursor
Ctrl + h – delete character before the cursor
Ctrl + t – swap character under cursor with the previous one

Command Recall Shortcuts

Ctrl + r – search the history backwards
Ctrl + g – escape from history searching mode
Ctrl + p – previous command in history (i.e. walk back through the command history)
Ctrl + n – next command in history (i.e. walk forward through the command history)
Alt + . – use the last word of the previous command

Command Control Shortcuts

Ctrl + l – clear the screen
Ctrl + s – stops the output to the screen (for long running verbose command)
Ctrl + q – allow output to the screen (if previously stopped using command above)
Ctrl + c – terminate the command
Ctrl + z – suspend/stop the command

Bash Bang (!) Commands

Bash also has some handy features that use the ! (bang) to allow you to do some funky stuff with bash commands.

!! - run last command
!blah – run the most recent command that starts with ‘blah’ (e.g. !ls)
!blah:p – print out the command that !blah would run (also adds it as the latest command in the command history)
!$ – the last word of the previous command (same as Alt + .)
!$:p – print out the word that !$ would substitute
!* – the previous command except for the last word (e.g. if you type ‘find some_file.txt /‘, then !* would give you ‘find some_file.txt‘)
!*:p – print out what !* would substitute

There is one more handy thing you can do. This involves using the ^^ ‘command’. If you type a command and run it, you can re-run the same command but substitute a piece of text for another piece of text using ^^ e.g.:

$ ls -al
total 12
drwxrwxrwx+ 3 Administrator None    0 Jul 21 23:38 .
drwxrwxrwx+ 3 Administrator None    0 Jul 21 23:34 ..
-rwxr-xr-x  1 Administrator None 1150 Jul 21 23:34 .bash_profile
-rwxr-xr-x  1 Administrator None 3116 Jul 21 23:34 .bashrc
drwxr-xr-x+ 4 Administrator None    0 Jul 21 23:39 .gem
-rwxr-xr-x  1 Administrator None 1461 Jul 21 23:34 .inputrc
$ ^-al^-lash
ls -lash
total 12K
   0 drwxrwxrwx+ 3 Administrator None    0 Jul 21 23:38 .
   0 drwxrwxrwx+ 3 Administrator None    0 Jul 21 23:34 ..
4.0K -rwxr-xr-x  1 Administrator None 1.2K Jul 21 23:34 .bash_profile
4.0K -rwxr-xr-x  1 Administrator None 3.1K Jul 21 23:34 .bashrc
   0 drwxr-xr-x+ 4 Administrator None    0 Jul 21 23:39 .gem
4.0K -rwxr-xr-x  1 Administrator None 1.5K Jul 21 23:34 .inputrc

Here, the command was the ^-al^-lash which replaced the –al with –lash in our previous ls command and re-ran the command again.

There is lots, lots more that you can do when it comes to using shortcuts with bash. But, the shortcuts above will get you 90% of the way towards maximum bash productivity. If you think that I have missed out on an essential bash shortcut that you can’t live without (I am sure I have), then please let me know and I’ll update the post. As usual, feel free to subscribe to my feed for more tips and opinions on all things software development.

SVN:IGNORE

Marqué :

Subversion ignore commands drive me up the wall. Git’s ignore is much easier to use, and consistent.

Here is the process I followed to add svn:ignore to a newly added directory that hadn’t yet been committed to the SVN repo. The magic here is the “-N” flag on the add command, since that stops the recursive add (which would add the git directories), and you can then set svn:ignore afterwards.

svn add active_scaffold_list_filters/ -N
svn ps svn:ignore ".git" active_scaffold_list_filters/
svn add active_scaffold_list_filters/*
svn ci

original : http://davidbolton.net/blog/2008/08/svnignore/

What’s the best way of handling permissions for apache2’s user www-data in /var/www ?

Marqué :

Avec des Acls

I think you may find POSIX ACL (access control lists) to be helpful. They allow a finer-grained permission model compared to the user:group:other model. I have found them to be easier to keep straight in my head since I can be more explicit and can also set the "default" behavior for a branch of the file system.

For example, you can specify each user's permissions explicitly:

setfacl -Rm d:u:userA:rwX,u:userA:rwX /var/www
setfacl -Rm d:u:userB:rwX,u:userB:rwX /var/www

Or you can do it based on some shared group:

setfacl -Rm d:g:groupA:rwX,u:groupA:rwX /var/www

And perhaps you want to keep your Apache user as read-only

setfacl -Rm d:u:www-data:rX,u:www-data:rX /var/www

Man pages:

Apt-Pinning for Beginners

Why apt-pinning?

Do you run Debian? Have you ever gotten annoyed at how Debian Stable always seems to be out of date?

I will show you a way that you can have apt mix-and-match between Stable, Testing, and Unstable sources. This will allow you to run a mostly-Stable system, but also track the latest and greatest of those packages that you are most keenly interested in.

Why do this? Stable is covered by the Security Team. Testing and Unstable are not. For non-critical services, like perhaps your mailer, or your window manager, this is not so important, and the newest versions may have additional features that are desired. It is these packages that are perfect for pinning to a version, other than Stable.

sources.list

The first step is to set up your /etc/apt/sources.list to include your typical Stable, plus the Testing/Unstable sources that you want.

A simple sources.list may look like this:

#Stable
deb http://ftp.us.debian.org/debian stable main non-free contrib
deb http://non-us.debian.org/debian-non-US stable/non-US main contrib non-free

#Testing
deb http://ftp.us.debian.org/debian testing main non-free contrib
deb http://non-us.debian.org/debian-non-US testing/non-US main contrib non-free

#Unstable
deb http://ftp.us.debian.org/debian unstable main non-free contrib
deb http://non-us.debian.org/debian-non-US unstable/non-US main contrib non-free

You would probably want to add your mirrors, security.debian.org, and perhaps the appropriate deb-src lines. Here is a copy of my actual sources.list.

preferences

The next step is to create/edit your /etc/apt/preferences file. preferences is where the apt-pinning takes place. Normally, the highest version of an available package wins, but we will override that.

A simple preferences file may look like this:

Package: *
Pin: release a=stable
Pin-Priority: 700

Package: *
Pin: release a=testing
Pin-Priority: 650

Package: *
Pin: release a=unstable
Pin-Priority: 600

Note the decending values. Since Stable has the highest pin-priority, it will be installed preferentially over Testing or Unstable.

My actual preferences file is what you see above.

apt-get update

Now we are ready to apt-get update. This will add the new repositories to apt's list.

E: Dynamic MMap ran out of room

You may find that you receive an error like the following:

E: Dynamic MMap ran out of room
E: Error occured while processing sqlrelay-sqlite (NewPackage)
E: Problem with MergeList /var/lib/apt/lists/ftp.us.debian.org_debian_dists_woody_contrib_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.

This is caused because apt's cache is too small to handle all of the packages that are included with stable, testing, and unstable. This is also very easy to fix. Add the following line to /etc/apt/apt.conf

APT::Cache-Limit "8388608";

Thanks to R (Chandra) Chandras for pointing out this problem

Installing new packages

To install a new package, it is just as it ever was, apt-get install <package>. If the package exists in Stable, then that is what it will grab. If the package exists only in Unstable, then from Unstable it will be gotten.

What if the package exists in both Stable and Unstable, but we want the Unstable version? There are two ways we can do that, each with a slightly different syntax, and each with a slightly different effect.

apt-get install <package>/unstable

This will install the unstable version of the package, and try to meet any dependencies from Stable. This may not work, but it will tell you why:

# apt-get install zsh/unstable
Reading Package Lists... Done
Building Dependency Tree... Done
Selected version 4.0.6-7 (Debian:unstable) for zsh
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

Sorry, but the following packages have unmet dependencies:
  zsh: Depends: libc6 (>= 2.2.5-13) but 2.2.5-11.1 is to be installed
E: Sorry, broken packages

apt-get -t unstable install <package>

This will install the Unstable version of the package, and try to meet any dependencies from Unstable. This may produce better results.

# apt-get -t unstable install zsh    
Reading Package Lists... Done
Building Dependency Tree... Done
The following extra packages will be installed:
  libc6 libc6-dev libc6-pic libdb1-compat locales 
The following NEW packages will be installed:
  libdb1-compat 
5 packages upgraded, 1 newly installed, 0 to remove and 394  not upgraded.
Need to get 11.6MB of archives. After unpacking 606kB will be used.
Do you want to continue? [Y/n]

That's it!

Armed with a complete sources.list and a minimal preferences, you can go ahead and mix-and-match between the various Debian releases.

Have fun!