Posted by gmendoza on September 23, 2009 under Tech Tips | 
Two great packages available to the Linux community are RAR and UNRAR. If you are already familiar with the RAR compression format, these allow you to create, modify and extract RAR archives. For those of you that appreciate the graphical compression application for Gnome called File Roller, these packages enable it to read RAR files. For more information about the RAR format, check out rarsoft.com.
To install from Ubuntu or Debian, its as simple as:
sudo apt-get install rar unrar
To list the files in a RAR archive, use the l or v option:
rar l video.rar
To decompress a RAR archive called video.rar, simply issue the command:
unrar e video.rar
The unrar package is only intended for decompression tasks. Otherwise, just use the rar command with the e option to extract the files to the current directory.
rar e video.rar
To compress a single file called video.avi, adding it to a RAR file called video.rar:
rar a video.rar video.avi
To compress a single file called video.avi, splitting it into approximately 50 Mb files:
rar a -v50000 video.rar video.avi
This by default creates archive files starting with video.part01.rar, video.part02.rar and following the sequence to completion. To use the older and better known extension sequence format of .rar, .r00, .r01, etc, use the -vn option like so:
rar a -v50000 -vn video.rar video.avi
To compress an entire directory recursively, use the -r option:
rar a -r Documents.rar Documents/
To extract the files from an archive, such that the original directory structure is also recreated, use the x command:
rar x Documents.rar
There are so many other features available to the RAR format, so be sure to check out the man pages or the packaged documentation.
man rar
less /usr/share/doc/rar/rar.txt.gz
(if your version of less supports reading of compressed files)
Posted by gmendoza on June 21, 2009 under Tech Tips |
I recently needed to organize a large number of old digital photos that had the wrong date embedded in their EXIF tag data. The camera I used many years ago would often lose track of time and would sometimes be set to the wrong year. Applications I now use to organize photos read this data and made my albums difficult to navigate. I came across a Linux command line utility called jhead that allows you to modify this information to whatever you wish, and its easy to use in scripts as well. Installing was easy, because it’s currently in most repositories, including Ubuntu’s.
To read existing EXIF tag data, simply run jhead against an image without any options. As you can see from the example below, my date is set to the year 2022.
jhead image.jpg
File name : image.jpg
File size : 159390 bytes
File date : 2004:01:12 07:35:23
Camera make : Samsung
Camera model : Digimax 200
Date/Time : 2022:02:12 04:04:17
Resolution : 800 x 600
Flash used : Yes
Exposure time: 0.045 s (1/22)
Aperture : f/2.8
To clear all EXIF data from the file, use the -de option. Then recreate the EXIF fields with the -mkexif option, and check the data again. Notice the new Date/Time is set to the timestamp on the file.
jhead -de image.jpg
Modified: image.jpg
jhead -mkexif image.jpg
Modified: image.jpg
jhead image.jpg
File name : image.jpg
File size : 147751 bytes
File date : 2004:01:12 07:35:23
Date/Time : 2004:01:12 07:35:23
Resolution : 800 x 600
To change the entire timestamp manually, use the -ts option. Notice, there is no space between the -ts and the option. I could not trust the month and day, so I simply chaged the date to midnight on January 1, 2003.
jhead -ts2003:01:01-00:00:00 image.jpg
Modified: image.jpg
jhead image.jpg
File name : image.jpg
File size : 147751 bytes
File date : 2004:01:12 07:35:23
Date/Time : 2003:01:01 00:00:00
Resolution : 800 x 600
For many more options, check out the man page or visit the jhead site for more info.
Posted by gmendoza on April 6, 2009 under Tech Tips |
Line wrapping text from the command line is easy with the fold utility, which of course is provided by the Free Software Foundation. By default, the fold command will wrap text at 80 characters, but you can of course specify the width manually. I prefer using the -s option, which will break only on spaces, making sure not to break in the middle of a word.
For example, the following command will concatenate a text file to standard output, adding line breaks only at spaces or at 72 characters, whichever comes first.
fold -s -w 72 textfile.txt
This can also be useful if you want to clearsign a message with Gnupg, but wish to line wrap it beforehand.
fold -s -w 72 textfile.txt | gpg --clearsign -u user@email.com
Add redirection if you wish to output the results to a file.
fold -s -w 72 textfile.txt > newfile.txt
As mentioned here, the fmt command also provides the same primary features of fold, but is much better. Not only does it wrap long lines, but it also fills out short lines as well. There are additional options that are worth looking into. Be sure to check out the man page!
man fmt
