GREP_COLORS – change the colors in the GREP output.

Today we will look at the variable GREP_COLORS. This variable determines the colour that is used with the grep command. You can look at the man page of the grep command to see what the various options mean. Here is the excerpt from the man command:

GREP_COLORS

          Specifies the colors and other attributes used to highlight various  parts  of  the
          output.   Its  value  is  a  colon-separated  list of capabilities that defaults to
          ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36  with  the  rv  and  ne   boolean
          capabilities omitted (i.e., false).  Supported capabilities are as follows.

          sl=    SGR  <a class="zem_slink" title="Substring" href="http://en.wikipedia.org/wiki/Substring" rel="wikipedia">substring</a>  for  whole  selected lines (i.e., matching lines when the -v
                 command-line option is omitted, or non-matching lines when -v is specified).
                 If however the boolean rv capability and the -v command-line option are both
                 specified, it applies to context matching lines  instead.   The  <a class="zem_slink" title="Default (finance)" href="http://en.wikipedia.org/wiki/Default_%28finance%29" rel="wikipedia">default</a>  is
                 empty (i.e., the terminal's default color pair).

          cx=    SGR  substring for whole context lines (i.e., non-matching lines when the -v
                 command-line option is omitted, or matching lines when -v is specified).  If
                 however  the  boolean  rv capability and the -v command-line option are both
                 specified, it applies to selected non-matching lines instead.   The  default
                 is empty (i.e., the terminal's default color pair).

          rv     <a class="zem_slink" title="Boolean data type" href="http://en.wikipedia.org/wiki/Boolean_data_type" rel="wikipedia">Boolean  value</a>  that  reverses  (swaps)  the  meanings  of  the  sl= and cx=
                 capabilities when the -v command-line option is specified.  The  default  is
                 false (i.e., the capability is omitted).

          mt=01;31
                 SGR  substring  for  matching  <a class="zem_slink" title="Empty set" href="http://en.wikipedia.org/wiki/Empty_set" rel="wikipedia">non-empty</a>  text in any matching line (i.e., a
                 selected line when the -v command-line option is omitted, or a context  line
                 when  -v  is specified).  Setting this is equivalent to setting both ms= and
                 mc= at once to the same value.  The default is a bold  red  text  foreground
                 over the current line background.

          ms=01;31
                 SGR substring for matching non-empty text in a selected line.  (This is only
                 used when the -v command-line option is omitted.)  The effect of the sl= (or
                 cx=  if  rv) capability remains active when this kicks in.  The default is a
                 bold red text foreground over the current line background.

          mc=01;31
                 SGR substring for matching non-empty text in a context line.  (This is  only
                 used  when  the -v command-line option is specified.)  The effect of the cx=
                 (or sl= if rv) capability remains active when this kicks in.  The default is
                 a bold red text foreground over the current line background.

          fn=35  SGR  substring  for file names prefixing any content line.  The default is a
                 magenta text foreground over the terminal's default background.

          ln=32  SGR substring for <a class="zem_slink" title="Line number" href="http://en.wikipedia.org/wiki/Line_number" rel="wikipedia">line numbers</a> prefixing any content line.  The default is a
                 green text foreground over the terminal's default background.

          bn=32  SGR substring for byte offsets prefixing any content line.  The default is a
                 green text foreground over the terminal's default background.

          se=36  SGR substring for separators that are inserted between selected line  fields
                 (:),  between context line fields, (-), and between groups of adjacent lines
                 when nonzero context  is  specified  (--).   The  default  is  a  cyan  text
                 foreground over the terminal's default background.

          ne     Boolean  value that prevents clearing to the <a class="zem_slink" title="Newline" href="http://en.wikipedia.org/wiki/Newline" rel="wikipedia">end of line</a> using Erase in Line
                 (EL) to Right (\33[K) each time a colorized item ends.  This  is  needed  on
                 terminals on which EL is not supported.  It is otherwise useful on terminals
                 for which the back_color_erase (bce) boolean terminfo  capability  does  not
                 apply,  when  the  chosen  highlight colors do not affect the background, or
                 when EL is too slow or causes too much flicker.  The default is false (i.e.,
                 the capability is omitted).

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.

Monitor your system with sysusage.

First some information on sysusage:

Description :
SysUsage continuously monitor your systems informations and generate
periodical graph reports using rrdtool or javascript jqplot library.
All reports are shown throught a web interface.

SysUsage grabs all system activities using Sar and system commands allowing
you to keep tracks of your computer or server activity during his life.
It is a great help for performance analysis and resources management. The
threshold notification can alarm you when the system capabilities are
reached by sending SMTP messages or throught Nagios reports.

Continue reading

bash – using the vi mode more effectively.

You can first set the bash mode to vi. This will enable some vim like features to bash. So, add this to .bashrc :

set -o vi

Once, you have done that then its time to get more out of the vi mode. First, check some things and set some interesting stuff.

procmail filters – apply to received mails.

If you already have some mail in your maildir and you have set procmail filters, then it is difficult to apply the procmail filter, right? Not so, you just need to go to the Inbox directory and then execute the command.

for i in *; do cat $i|procmail; rm -f "$i"; done

This will pass all of your e-mail through procmail again and then your filters will get applied. Mails will go to their appropriate directory and you will be one happy man, I hope.

slow ssh connection

If you are experiencing slow ssh connections, then possibly your system is trying to do reverse lookup of the IP address. If that is the case, then you can add the below to “hosts” line in /etc/nsswitch.conf file.

‘[NOTFOUND=return]’

The other cause for slow connections can be GSSAPI authentication. If that is the case, then the simplest solution is to add the following in your “~/.ssh/config” file:

poor mans watch, watch for solaris

Here is a simple script that you can use as watch in Solaris as well.

watch()
{
    #Poor man's watch
    while (true)
    do
        clear
        $*
        sleep 2;
    done
}