Updating rubygems on Ubuntu
If you have ever tried to update rubygems on a base Ubuntu 10.04 or 10.10 install you will have been greeted with:
ERROR: While executing gem ... (RuntimeError)
gem update --system is disabled on Debian. RubyGems can be updated using the official Debian repositories by aptitude or apt-get.
You can work around this limitation:
# /var/lib/gems/1.8/bin/update_rubygems
You will now be able to update rubygems using the standard set of commands.
Reformat and reindent an XML file
This is easy to accomplish with xmllint and a shell one-liner:
Replace Pipes with Tabs in a Delimited File
Issue:
It is often necessary to replace delimiters in a file with a form the receiving party expects. sed is my favorite method of meeting the need.
Solution:
Replace double pipes with tabs
Note: If you find the tab key simply does not work, try CTRL+V+I from your terminal.
Reference: http://forums.devshed.com/unix-help-35/replacing-tabs-with-spaces-372623.html
Caveats:
Special consideration (and a regex) will be required for data where delimiters are present in the data itself. Consider your use case and apply appropriately.
Create a pidof command to find PID numbers easily
Most UNIX environments include the pidof command which is put to use whenever one needs to quickly determine, by name, the pid of a running program. Apple's Mac OS X lacks the pidof command, however, one may approximate its function with the following shell script:
ps axc|awk "{if (\$5==\"$1\") print \$1}";
Save the script as /bin/pidof and be sure to set its executable bit:
Strip empty (null) lines from a file
sed meets the need; the recipe follows:
Mirror a Directory Structure Using the Command Line
Issue:
You need to mirror the directory structure (but not contents) for a tree.
Resolution:
Execute the following command from the root of your source directory. Adjust the destination variable to suit your tastes: %i will match the first token, %j the second, %k the third, and %l will match everything else.
Reference: http://www.dostips.com/DtTipsStringManipulation.php
rsync failed to set times on [filename]
This error occurs because the version of rsync on the system cannot preserve modified times for directories.
Run rsync with the following arguments to suppress this warning:
rsync -avPO ./source/* ./destination
Explanation of switches:
1 2 3 4 | a -> Archive mode (do not preserve hard links, ACLs, or extended attributes) v -> Verbose (I like to know what is happening) P -> Equivalent to --partial --progress (for long transfers that may be interrupted) O -> Omit directories from times |
Create thumbnails en-masse from a bash prompt
A simple one-liner and ffmpeg, basename, and cut gets this done.
1 | for i in *.f4v; do ffmpeg -i `basename $i` -s 320x240 `basename $i | cut -d'.' -f1`.jpg; done |
Thumbnail output size is configurable with the -s switch.
Count the number of characters (or columns) in a file
Sometimes you want to count the number of characters or columns in a file.
1 | awk 'length>max{max=length}END{print max}' filename.txt |
For extraordinarily long or wide data sets you may want to consider the following:
1 | head -n 10 | awk 'length>max{max=length}END{print max}' |
OR
1 | tail -n 10 | awk 'length>max{max=length}END{print max}' |
Convert text file to UTF-8 encoding from the shell
1 | for f in *.txt; do iconv -f mac -t utf-8 "$f" >"$f.utf8"; done |
Note:
-f Input file encoding type
-t Output file encoding type
Reference: http://manual.macromates.com/en/saving_files.html