better bash debugging

I was trying to debug some bash scripts yesterday and learnt something new 😉
There are lot of things in bash that you can use to debug and to start with you can enable xtrace mode as follows:

set -x

With this set you will see that all the commands are printed along with all other information as they are executed.
This you can do for any line or for the function or for the whole script. Once you set the option you can turn it
off with

[Solved] ssh works but scp does not

For quite sometime now, I was having this issue, that for the home system, I was able to connect to is using ssh but it never worked. Fnally after quite some debugging finally I found that the issue was with thebashrc. So, everytime I had to do a scp I would have to move/rename bashrc and do the reverse action after the scp was done.

bash completion

I was working on some functions in bash to make my life easier and realized that if I added custom completion to my functions, it will be really good. So I headed over to google and searched for what I wanted. I did get a lot of information on bash completion but not a single concrete example that could help me do what I wanted. So, with the help of man pages and some results from the Google pages, I was finally able to accomplish what I wanted. So here it is:

faster bash operations on files with File Descriptors.

I was writing a bash script that would do some operations and read and write to file. Seems that that was pretty simple with

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      while read line<br /> <br /> do<br /> <br /> done<file
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</tr>

and then use redirection operations like “>” and “»” to write to file. Done with the script pretty fast. So far so good, when I went for real life tests, no one was interested in using it, why? Simple, it was simply taking too long. The file was reading about 10K lines and writing about 50 lines and was taking about more than 10 minutes.

Total upload and download on any interface.

Something that I have been searching for a long time, finally some look inside the <a class=“zem_slink” title=“Procfs” rel=“wikipedia” href=“http://en.wikipedia.org/wiki/Procfs" _mce_href=“http://en.wikipedia.org/wiki/Procfs">/proc got me what I wanted. Hope this will save someone’s day. So far, the only option I could think of was to run conky which becomes a little heave on some of the very old laptops I have to use sometimes 🙁

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      &nbsp;cat /proc/net/dev|grep eth2|awk '{print $2/1024/1024"&nbsp; "$10/1024/1024}'
    </div>
  </td>
</tr>

Related articles

• CPUSPEED Slowing you down? (jarneil.wordpress.com)
• Interface Curmudgeons versus Gestures (lingpipe-blog.com)
• Alias in .bashrc (michaeldaranto.wordpress.com)

Unix shell script for removing duplicate files

The following shell script finds duplicate (2 or more identical) files and outputs a new shell script containing commented-out rm statements for deleting them (copy-paste from here):

::: updated on 02 May 20121, seems like wordpress did not like it so well so reformatting the code :::::::

#!/bin/bash -
#===============================================================================
#
#          FILE:  a.sh
#
#         USAGE:  ./a.sh
#
#   DESCRIPTION:
#
#       OPTIONS:  ---
#  REQUIREMENTS:  ---
#          BUGS:  ---
#         NOTES:  ---
#        AUTHOR: Amit Agarwal (aka), amit.agarwal@roamware.com
#       COMPANY: blog.amit-agarwal.co.in
#       CREATED: 02/05/12 06:52:08 IST
# Last modified: Wed May 02, 2012  07:03AM
#      REVISION:  ---
#===============================================================================

OUTF=rem-duplicates.sh;
echo "#!/bin/sh" >$OUTF;
find "$@" -type f -exec md5sum {} \; 2>/dev/null | sort --key=1,32 | uniq -w 32 -d |cut -b 1-32 --complement |sed 's/^/rm -f/' >>$OUTF

Pretty good one line, I must say 🙂

mysql output to an array for easy parsing.

Today I was looking for some way to put the output of the mysql output in an array in a bash script. Quick google search yeilded to results something like this:

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      output=$(mysql -e "select * from table")
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</tr>

The problem with the above approach is that all the words go into separate index. So if you have a line that has space then that is split into multiple index’s. Not good…