Shell Programming and Scripting

Hi radoulov,

thanks a lot

i have got one more query

i have one file cpu and its content are:

Data Collected: 05/17/08 17:19:49

Refresh Interval: 600 seconds

GlancePlus Started/Reset: 05/17/08 08:19:45
B3692A GlancePlus C.03.72.00 17:29:49 UXAMSK01 9000/800 Current Avg High
-------------------------------------------------------------------------------
CPU Util SSUUUUU | 16% 9% 22%
Disk Util F | 1% 5% 12%
Mem Util SSSSSSSSSSUUUUUUUUBBBBB | 46% 45% 46%
Swap Util UUUURRRRR | 17% 16% 17%
-------------------------------------------------------------------------------
IO BY FILE SYSTEM Users= 8
Idx File System Device Type Logl IO Phys IO
--------------------------------------------------------------------------------
1 / /dev/vg00/lvol3 vxfs 24.8/ 25.1 0.5/ 0.5
2 /stand /dev/vg00/lvol1 hfs 0.0/ 0.0 0.0/ 0.0
3 /var /dev/vg00/lvol8 vxfs 0.2/ 0.3 1.9/ 2.1
4 /usr /dev/vg00/lvol7 vxfs 35.2/ 17.7 0.9/ 0.7

Top disk user: PID 11053, s_server 10.0 IOs/sec S - Select a Disk


Now i m using this code

sed -n '1p;8,10 {;s/^\([^ ]*\) [^0-9]*\([0-9]*%\).*$/\1 \2/p;}' cpu

to get output as:

Data Collected: 05/17/08 17:19:49
CPU 16%
Disk 1%
Mem 46%

i want to know few things about this code as to how it works
{;s/^\([^ ]*\) [^0-9]*\([0-9]*%\).*$/\1 \2/p;};
specially difference between ^ individually and like this [^ ]* and in this case
how it will directly take the second part of output i.e the % part bcoz in line 8-10
the % part comes after delimeter '|' so how does it actually work

and [^0-9]*\([0-9]*%) does it mean starting from 0-9 any character followed by 0-9 any charcter with % symbol

and what does this .*$ mean

and lastly this \1 \2/p;}; how does it work

Please help me





s/^\([^ ]*\)

Seems cut just doesn't cut it nowadays

Code:

$ cut -d"/" -f3 < infile | cut -d":" -f1
name1
name2
name3

The difference between ^ and [^] is that in the first case the caret ^ is a meta-character that matches the beginning of the line
(it's a zero-length match, it matches the empty space at the beginning of the string, not the first character of the string).

The $ character matches the end of the line/string.

They are called anchors.

In the second case the brackets [] denote a character class. If the first character of the list is the caret ^ then it matches any character not in the list,
so [^ ] matches any character different than a space (you have a space after the ^ character).

In this case we have:

Code:

 ^\([^ ]*\)

The first group of parentheses () saves any number of occurrences (because of the * after the complemented character class [^ ])
of non-space characters [^ ]. As far as the following string is concerned:

Code:

CPU Util SSUUUUU | 16% 9% 22%

It's the following string:

Code:

CPU

Followed by:

Code:

 [^0-9]*\([0-9]*%\).*$

A space, any number of occurrences of the following complemented character class [^0-9], i.e., any non-digit character. In this case the string:

Code:

 Util SSUUUUU |

Then we save the string matching the following regular expression:

Code:

\([0-9]*%\).*$

any number of occurrences (*) of the indicated character class [0-9] - only digits, followed by the % character,
followed by any number of occurrences (*) of any character . (dot).

It's the following string:

Code:

16%

You can refer to the previously saved matches using the spacial syntax \1, \2 and so on.

Hope this helps.

Hi radoulov,

when we have given this ([^ ]*\) in our code it will search for any charcter different than space so according to that
our output should be this

CPU Util SSUUUUU | 16% 9% 22%

how its coming to only
CPU

similarly in this part [^0-9]*\([0-9]*%\).*$
we are first searching for any charcter different than 0-9 so the output should be

CPU Util SSUUUUU |

after that it searches for 0-9 with %
so the output should be

16% 9% 22%

and how its coming

16%

and thanks for the earlier response
it cleared many doubts of mine
but still have some doubts that i would like to clear

thanks
haris

and radoulov u mentioned any number of occurrences with the help of *

but in this case ([^ ]*\) it will match for any character different than space
that means entire string of ours that is

CPU Util SSUUUUU | 16% 9% 22%

than why you have written only

CPU

how did we get that
similarly for ([0-9]*%\).*
please explain this in detail

thanks
haris

So, we have three characters different than a space and then a space: C, P, U and space, so from 0 to infinity no-space characters, the longest match is CPU:

Code:

% print 'CPU Util SSUUUUU | 16% 9% 22%'|sed -r 's/^([^ ]*).*/-->\1<--/'  
-->CPU<--

First of all, when the sed regular expressions engine tries to match that pattern, the string CPU is already consumed by the first match.
So it now is trying to match from the space that follows the string CPU onwards and, considering the string above, we have: a space, U, t, i, l, a space, S, S, U, U, U, U, U, one more space, pipe and another space and this string is matched by the following regular expression: [^0-9]*:

Code:

% print 'CPU Util SSUUUUU | 16% 9% 22%'|sed -r 's/^([^ ]*)( [^0-9]*).*/-->\1<-- -->\2<--/'
-->CPU<-- --> Util SSUUUUU | <--

And now the final part: [0-9]*%. The sed regular expressions engine is searching from the space after the pipe (excluding the space itself) onwards. It tries to match any number of digits followed by the % character, so it matches only 16%:

Code:

% print 'CPU Util SSUUUUU | 16% 9% 22%' |
  sed -r '
    s/^([^ ]*)( [^0-9]*)([0-9]*%).*$/-->\1<-- -->\2<-- -->\3<--/
'
-->CPU<-- --> Util SSUUUUU | <-- -->16%<--

If we had included a space and the % character in our character class, we would have matched the entire string,
leaving nothing for the last .*$ part:

Code:

% print 'CPU Util SSUUUUU | 16% 9% 22%' |
  sed -r '
    s/^([^ ]*)( [^0-9]*)([0-9 %]*%)(.*$)/-->\1<-- -->\2<-- -->\3<-- -->\4<--/
'                                                                           
-->CPU<-- --> Util SSUUUUU | <-- -->16% 9% 22%<-- --><--

Because the * mean 0 or more. If we force the last regular expression to match 1 or more[1] (not 0 or more) characters,
the result will be different:

Code:

% print 'CPU Util SSUUUUU | 16% 9% 22%' |
  sed -r '
    s/^([^ ]*)( [^0-9]*)([0-9 %]*%)(.+)$/-->\1<-- -->\2<-- -->\3<-- -->\4<--/
'                                                                           
-->CPU<-- --> Util SSUUUUU | <-- -->16% 9%<-- --> 22%<--

[1]. Only a few sed implementations support extended regular expressions (the + quantifier).

if you have bash

Code:

while read line
do
 line=${line##*/}
 line=${line%:*}
 echo $line
done < file