Showing posts with label fedora. Show all posts
Showing posts with label fedora. Show all posts

Tuesday, 16 October 2012

Practical ls Command Examples For Fun & Profit

The power of linux lies in the shell through which we can perform complex job in no time. While the directory listing command 'ls' seems to be very simple command, the linux shell provides the power to use switches and pipes to do anything from terminal. Check out this list with practically useful examples using ls.

Display all files including hidden files/folders

ls -a


Display one file/folder per line

ls -1


Count number of files & folders

ls -1 | wc -l


Human readable file sizes (eg. Mb or Gb)

ls -lh


Alphabetically sort the listing

ls -X


Only list the folders in current directory

ls -d */
ls -p | grep /




Display folders in current directory consisting certain patterns

ls -l D* | grep :$
ls -l *a* | grep :$


List files by descending order of modification time

ls -lt
ls -l --sort=time #alternative long version


List files by descending order of creation time

ls -lct


List files in reverse order

ls -ltr
ls -l --sort=time --reverse #alternative long version


List files in descending order of file size

ls -lSh
ls -lh --sort=size
ls -lSh1 *.avi #find largest AVI file
rm `ls -S1 | head -1` #delete largest file in current folder


List files in ascending order of file size

ls -lShr
ls -lh --sort=size --reverse #alternative long version


Display directories in recursive manner

ls -R


Display the files/folders created today

ls -l --time-style=+%F | grep `date +%F`


Display the files/folders created this year

ls -l --time-style=+%y | grep `date +%y`


Any more example that fires up in your mind? Feel free to share over here ;)


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Monday, 3 September 2012

Preventing Accidental Overwriting Of Files In Bash Shell

How many times has this happened to you? It used to happen once in a while with me. A Linux user learns to use the redirection operators such as '>' and '>>' but accidental overwriting starts to become common in commands you use and shell scripts you write.

The accidental overwriting of files that happens unintentionally is known as clobbering and it commonly happens while using the '>' redirection operator.

samar@Techgaun:~$ mycmd > myfile

In the above example, the mycmd clobbers any existing data in the myfile file if that file exists already. Worse things may happen sometime. Imagine accidentally typing

samar@Techgaun:~$ mycmd > /etc/passwd

instead of possibly using other redirection operators (like >> or <). Thankfully, you could recover /etc/passwd from either /etc/passwd- or /var/backups/passwd.bak if you hadn't rm'd these files.

To prevent such accidental overwriting, we can set the noclobber environment variable. Below is a session of enabling this variable:

samar@Techgaun:~/Desktop/test$ echo "www.techgaun.com" > myfile
samar@Techgaun:~/Desktop/test$ echo "Overwriting techgaun.com" > myfile
samar@Techgaun:~/Desktop/test$ set -o noclobber
samar@Techgaun:~/Desktop/test$ echo "Retrying to overwrite" > myfile
-bash: myfile: cannot overwrite existing file

As seen above, you have to turn on the noclobber variable using the set -o noclobber command in your shell. However, you might want to intentionally overwrite contents of certain files even when the noclobber is turned on.

samar@Techgaun:~$ mycmd >| myfile

Notice the >| in place of your normal > redirection operator. Using this operator, you can however overwrite the existing files even if the noclobber is turned on.

If you want to turn off the noclobber variable, type the following:

samar@Techgaun:~$ set +o noclobber

You can also permanently turn on the noclobber by the following command:

samar@Techgaun:~$ echo "set -o noclobber" >> ~/.bashrc

Moreover, such accidental overwriting can be prevented by enabling the interactive mode which is available in most of the linux commands. For example, you can write the alias for many commands that are likely to cause accidental overwriting. See some examples of aliases below:

samar@Techgaun:~$ alias rm=rm -i
samar@Techgaun:~$ alias mv=mv -i

You could even keep these aliases in your ~/.bashrc file permanently. Enabling such interactive modes by default in the commands that are more likely to cause accidental overwriting can prevent clobbering in many cases.

I hope this proves useful to you :)


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Sunday, 2 September 2012

How To Search Manual Pages In Linux

Linux system consists of hundreds of binaries, several syscalls, and other stuffs that do have manual page. What if you want to locate or find the commands by searching through the manual pages? In this post, I am going to talk about one such useful command to search through the manual page names and short descriptions.

The command I am talking about is the apropos command. The best way to learn any linux command is to read its corresponding manual and go through the help (-h or --help) so lets poke through the help of apropos itself.

samar@Techgaun:~$ apropos -h
Usage: apropos [OPTION...] KEYWORD...

  -d, --debug                emit debugging messages
  -v, --verbose              print verbose warning messages
  -e, --exact                search each keyword for exact match
  -r, --regex                interpret each keyword as a regex
  -w, --wildcard             the keyword(s) contain wildcards
  -a, --and                  require all keywords to match
  -l, --long                 do not trim output to terminal width
  -C, --config-file=FILE     use this user configuration file
  -L, --locale=LOCALE        define the locale for this search
  -m, --systems=SYSTEM       use manual pages from other systems
  -M, --manpath=PATH         set search path for manual pages to PATH
  -s, --section=SECTION      search only this section
  -?, --help                 give this help list
      --usage                give a short usage message
  -V, --version              print program version

Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.

The --regex option is enabled by default.

Report bugs to cjwatson@debian.org.

Particularly, the -e switch is quite useful to filter out your search. See the example below:

samar@Techgaun:~$ apropos -e tar
bf_tar (1)           - shell script to write a tar file of a bogofilter direc...
bf_tar-bdb (1)       - shell script to write a tar file of a bogofilter direc...
git-tar-tree (1)     - Create a tar archive of the files in the named tree ob...
lz (1)               - gunzips and shows a listing of a gzip'd tar'd archive
mxtar (1)            - Wrapper for using GNU tar directly from a floppy disk
ptar (1)             - a tar-like program written in perl
tar (1)              - The GNU version of the tar archiving utility
tar (5)              - format of tape archive files
tgz (1)              - makes a gzip'd tar archive
uz (1)               - gunzips and extracts a gzip'd tar'd archive

Each command has its associated short description and the apropos command searches the short description section of appropriate manual page for the provided keyword. You can also specify the search keywords in the form of regular expression for more flexibility. I hope this command counts as useful one :)


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Monday, 27 August 2012

How To Manually Install Flash Player 11 In Linux

This post will provide a step by step instructions for installing flash player 11 plugin in ubuntu 11.04 and other different versions and distros. This will be helpful for everybody who are having trouble with the software center like I had.


Make sure no firefox process is running and then fire up the terminal and type the following commands in order:

mkdir -p ~/flash && cd ~/flash

wget http://archive.canonical.com/pool/partner/a/adobe-flashplugin/adobe-flashplugin_11.2.202.238.orig.tar.gz

tar -zxvf adobe-flashplugin_11.2.202.238.orig.tar.gz

sudo cp -r libflashplayer.so /usr/lib/firefox/plugins

sudo cp -r usr/* /usr

Once you have finished copying the shared object and other necessary files in their respective target directories, you can open the firefox and you're good to go. :)


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Monday, 13 August 2012

Screen Recording Software Solutions For Linux

Windows users have several options to choose from when it comes to the desktop recording (and only paid ones are good generally) but Linux users have fewer options but robust, simple, and best of all, free and open source desktop screen recording tools that we can trust on.

Below are some of the screen recording tools you might want to try:

recordMyDesktop


recordMyDesktop is a desktop session recorder for GNU/Linux written in C. recordMyDesktop itself is a command-line tool and few GUI frontends are also available for this tool. There are two frontends, written in python with pyGtk (gtk-recordMyDesktop) and pyQt4 (qt-recordMyDesktop). recordMyDesktop offers also the ability to record audio through ALSA, OSS or the JACK audio server. Also, recordMyDesktop produces files using only open formats. These are theora for video and vorbis for audio, using the ogg container.

Installation under debian and ubuntu:

sudo apt-get install gtk-recordmydesktop

XVidCap


XVidCap is a small tool to capture things going on on an X-Windows display to either individual frames or an MPEG video. It enables you to capture videos off your X-Window desktop for illustration or documentation purposes.It is intended to be a standards-based alternative to tools like Lotus ScreenCam.

sudo apt-get install xvidcap

Istanbul


Istanbul is a desktop session recorder for the Free Desktop. It records your session into an Ogg Theora video file. To start the recording, you click on its icon in the notification area. To stop you click its icon again. It works on GNOME, KDE, XFCE and others. It was named so as a tribute to Liverpool's 5th European Cup triumph in Istanbul on May 25th 2005.

sudo apt-get install istanbul

Vnc2Flv


Vnc2flv is a cross-platform screen recording tool for UNIX, Windows or Mac. It captures a VNC desktop session (either your own screen or a remote computer) and saves as a Flash Video (FLV) file.

Wink


Wink is a Tutorial and Presentation creation software, primarily aimed at creating tutorials on how to use software (like a tutor for MS-Word/Excel etc). Using Wink you can capture screenshots, add explanations boxes, buttons, titles etc and generate a highly effective tutorial for your users. It requires GTK 2.4 or higher and unfortunately is just a freeware(could not find any source code for it).

Screenkast


Screenkast is a screen capturing program that records your screen-activities, supports commentboxes and exports to all video formats.

If you got any more suggestions, please drop the comment. :)


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Wednesday, 18 July 2012

Why Alias Command With Itself

Aliasing the command to itself to suppress the original functionality of the command and provide it new added sets of functionality can come quite handy for linux users and administrators.

If you have been using linux shell for a while, I'm pretty sure you are now familiar with the `ls` command, if not I think you have just learnt to use man pages. Probably you've been using `ls -l` command to list files with the files size as well. Too bad, you won't just be able to instantly make the sense of the file size displayed using this command so why not alias `ls` command to always provide human readable file sizes. So here is my alias:

alias ls='ls -lh'


This is what I always want to see as the output with `ls` command. The same kind of alias can be used with `du` and `df` commands. There are number of other cases where aliasing a command with itself is good choice.

Another example is the less command. By default, you need to press q to exit less which can be quite annoying if the entire content can fit in a single screen. However, adding -F flag will gracefully quit after displaying the content if the content fits in a single screen. So I have my alias for less as below:

alias lesss='less -F'


If something shoots in your mind, feel free to share here as a comment :)


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Friday, 13 July 2012

Stack-based Directory Switching For Easy Reversal

So how many times have you used the `cd` command repeatedly to go back and forth of two or more directories. Probably you are already familiar to the `cd -` command which lets you switch between the current and the previous directory. But, many times this current and previous directory switching restriction will not suffice and hence a better option in such case is to use the `pushd` command instead of `cd`.

For example, just use the `pushd somedirA`, `pushd somedirB`, ... and like that. Now if you need to switch back, you can just use `popd` command and you'll be switching back easily. The `pushd` command saves the current directory path and then cds to the supplied path.

If you dig more, you'll come to know about the -n and -N switches you can combine with these commands so I will let you explore on this. Also, you can use the `dirs` command to view the stack of directories. If you are some computer student or enthusiast, you have already gotten an idea from a famous data structure called stack. Anyway, I hope this comes handy sometimes like it does to me :)


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Friday, 15 June 2012

Recover Deleted Files From An NTFS Volume Using Ntfsundelete

Ntfsundelete is a part of ntfsprogs, a suite of NTFS utilities based around a shared library. It lets us recover the deleted files from any NTFS volumes without making any changes in the NTFS volume itself.

Generally when a file is deleted from disks, it is some kind of pointer to the physical file that gets deleted and the actual content still remains in the disk unless it is overwritten by new files so it is possible to recover those files.

ntfsundelete has three modes of operation: scan, undelete and copy. By default, it will run in the scan mode which simply reads an NTFS volume and looks for the files that have been deleted.



To use ntfsundelete, you'll have to install the ntfsprogs suite with following command in ubuntu and debian-based distros:

samar@Techgaun:~$ sudo apt-get install ntfsprogs

You'll have to first figure out which drive you want to recover. A handy command for this is:

samar@Techgaun:~$ sudo fdisk -l

Once you know the NTFS volume you want to recover, you can first run the scan mode to list the filenames that can be recovered.

samar@Techgaun:~$ sudo ntfsundelete /dev/sda4

The optional -f switch can be specified for the forceful scanning. There is a nice percentage field which gives the information on how much of the file can be recovered. You can apply the time and percentage filters to scan specific files. For example, you can use the following command to search for the files which can be recovered 100%

samar@Techgaun:~$ sudo ntfsundelete -p 100 /dev/sda4

And, you can apply the time filter to list the files altered/deleted after the specified time. For example, following command will scan and list the files deleted in the last 14 days.

samar@Techgaun:~$ sudo ntfsundelete -p 100 -t 2d /dev/sda4

Other suffices you can use are d, w, m, y for days, weeks, months or years ago respectively.

Once you get the files to be recovered, you can use the -u switch to undelete or recover the files. An example of recovering files by pattern matching is as below:

samar@Techgaun:~$ sudo ntfsundelete -u -m *.jpg /dev/sda4

Similarly you can recover by providing inode or inodes range using the -i switch. You can get the inode values from the first column in the scan mode.

samar@Techgaun:~$ sudo ntfsundelete -u -i 161922 /dev/sda4


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