bash debug – log all executed commands

Whenever I am writing a script in perl or bash, I always wish that there
was some way to have all the commands logged or output to screen. I know
there is “set -x” option to have debugging enabled, but sometimes that
seems to be too much information and I dont really need all that. So, here
is something I found recently for bash to log all the executed commands.

vim maps – simple commands to do stuff.

Some time back, I was working on some script for logging and I wanted to change the class to function like this:

$logger->Debug("Test string");
loggerFunc("Debug", "Test String");

As you can see, this change could be quite frustrating if you have quite a few references. And thus vim comes to rescue.

Simple map like ::

:map ,mm :s/(.*)$logger->(.*)((.*)).*/1loggerFunc("2",3);/

and then I can do “/$logger->” and then “n” to go to next match. Just do “,mm” and the line is re-factored.

convert tabs to spaces, the easy way

Lots of times you want to convert tabs to spaces and sometimes from a shell script, if that is the case, then simple solution is “tidy“. First you need to install tidy as follows:

sudo yum install tidy

and then you can use the command tab2space.

tab2spcae

This will print the output to STDOUT by default which you can redirect if you want.

Compare files excluding certain lines.

Quick tip, you can use any expression for the sed commands in the (). With this trick you can redirect the stdout of 2 commands to the diff command. This might become very useful, if you want to compare 2 files, excluding the first  line.

diff <(sed '1d' file) <(sed '1d' file2)

More interesting example is where the string ABC is converted to abc before comparing in the second file with the following command:

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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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.

Terminating a SSH session after starting background process.

This is too good. If you are planning to start a background process in the bash script in the background and continue in the script, you cannot do it until…….

You would need to close the stdout/stdin and stderr before you can terminate any ssh session automatically. Here’s some more light on this topic.

http://lists.debian.org/debian-user/2005/09/msg00254.html

On Thu, Sep 01, 2005 at 05:33:28PM -0400, Roberto C. Sanchez wrote: > I occasionally log into a machine remotely and start a process in the > background: > > command & > > However, when I log out of the machine, the ssh process on my local > machine blocks. I guess that it is becuase the remote still has jobs > running. Is there a way to get it start the process in the background > and then detach from the shell? I have already tried this:

write the output of a command to /var/log/user.log… each line will contain $USER, making this easy to grep for.

write the output of a command to /var/log/user.log… each line will contain $USER, making this easy to grep for.

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      &nbsp;log() { (echo "$ $@";$@) | logger -t $USER; }
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This command is useful if you want to copy the output of a series of commands to a file, for example if you want to pastebin the output from ‘uname -a’, ‘lspci -vvv’ and ‘lsmod’ for video driver trouble-shooting on your favorite Linux forum.