script for executing a program and doing string comparison

b-neva · 05-06-2009, 01:48 PM

Hi there,

I am fairly new to linux still and I'm currently trying to write a shell script (which I have never done) that is supposed to run the xrestop(like top) program. What I want to do is execute the program and check the identifier column to see if a certain program is running. If it is running I want to strip the data from that row of the terminal say every 5 seconds or so and put it in a text file. Is this going to be a complicated thing? Any ideas?

heres a list of the columns when you run xrestop program

res-base Wins GCs Fnts Pxms Misc PxmMem Other Total PID Identifier

Thanks

Sergei Steshenko · 05-06-2009, 02:28 PM

man cut

b-neva · 05-06-2009, 02:40 PM

Quote:

Originally Posted by Sergei Steshenko

man cut

but that's only for files correct? xrestop is running in the terminal and I was wondering if I could search it while it's running and then put it to a file.

raconteur · 05-06-2009, 03:52 PM

It seems to me that it would be easier and more straightforward to write a simple shell script to parse the process tree (man ps) and write the result to the status file.

colucix · 05-06-2009, 03:59 PM

If you use the option -b you can take a snapshot into the standard output. To catch it every 5 seconds, use sleep 5 and embed your code in an infinite loop, for example

Code:

#!/bin/bash
while true
do
  xrestop -b | grep some_app | some other commands here
  other commands here
  sleep 5
done

b-neva · 05-07-2009, 02:38 PM

Code:

while true
do    
    memory=`ps -eo vsz,cmd | grep spry | cut -f 1 -d \ `
    memory=`echo $memory / 7500 | bc`
    i=0
    while [$i -lt $memory]
    do
    	echo -n "="
    	i = `echo $i + 1 | bc`
    done
    echo
done

this is what I have so far, it's not working once I put the while loop in (I think my syntax/logic is just wrong). What I am trying to do is get the memory/7500 so I have a small number usually in the 20-30 range and get it to print out that many = so by the end I will have somewhat of a "graph"

Code:

memory=`expr $memory/7500`;echo $memory

Just another question, I had this instead of the "memory=`echo $memory / 7500 | bc`" statement but it would just print out the value of memory then 5000. So like 2553435000 instead of the actual evaluation, what was I doing wrong?

colucix · 05-07-2009, 02:49 PM

The only problem I see in your script is the incorrect usage of blank spaces:

1) put blank space around the square brackets:

Code:

[ $i -lt $memory ]

2) don't put blank spaces around the = sign in an assigment:

Code:

i=`echo $i + 1 | bc`

3) put blank spaces around the arithmetic operator:

Code:

expr $memory / 7500

b-neva · 05-07-2009, 03:02 PM

Ok I tried your fixes.

Code:

memory=`expr $memory / 7500`

if I try this, I get an expr syntax error, it won't work unless I have no spaces between $memory/7500

Quote:

(standard_in) 1: syntax error
./memory.sh: line 6: [: 0: unary operator expected

Ok so I get this I think just because it's trying to find the "spry" program but doesn't find it. If I am running the program then it stops the errors and starts printing the "=" now I just have a few logic problems to workout with that.

thanks

colucix · 05-07-2009, 03:17 PM

Yes, when the variable memory is not allocated (it has zero length) you get a bunch of syntax errors. You can avoid the problem adding a simple test:

Code:

memory=`ps -eo vsz,cmd | grep spry | cut -f 1 -d \ `
if [ -n "$memory" ]
then
  your commands here
fi

Another note: you can modify the ps command to retrieve just the virtual memory size of the spry process (if any):

Code:

ps -o vsz= -C spry

this will look for the spry process only and will give just the memory, without the header (see the = sign after vsz).

b-neva · 05-07-2009, 03:52 PM

Alright, the program seems to be doing what it's supposed to be doing. Thanks a lot for your help I appreciate it.