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How to pass cat file in awk statement?

 
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# 1  
Old 04-16-2015
How to pass cat file in awk statement?
Hi,

I am working on kernel parameters, want to check values under /proc/sys/kernel

below I tried for kernel.sem

Code:
 
SEMMNS:    4096              cat /proc/sys/kernel/sem | awk '{print $2}'
 
awk '{ if ($2 < 33000) print }' /proc/sys/kernel/sem |awk '{print $2}'
32000
The above awk worked.

I am also trying for

Code:
 
SHMMAX:     2145745cat /proc/sys/kernel/shmmax
I am trying below awk, but it is not working

Code:
 
awk '{if ($(cat /proc/sys/kernel/shmmax) > 200) print}' /proc/sys/kernel/shmmax
awk: (FILENAME=/proc/sys/kernel/shmmax FNR=1) fatal: division by zero attempted


# 2  
Old 04-16-2015
What operating system are you using?

Why the 2nd awk is failing is clear:
Code:
$(cat /proc/sys/kernel/shmmax)

in an awkscript is an attempt to look at the contents of the field specified by dividing the value of the awk variable cat by the value of the awk variable proc ... divided by the value of the awk variable shmmax. And, since none of those awk variables are defined in your awk script, they all evaluate to 0 (i.e., $(0/0/0/0)) which dies on the attempt to divide by 0.

What you are trying to do is not clear. What output do you get from the command:
Code:
cat /proc/sys/kernel/shmmax

when you type it into your shell?
# 3  
Old 04-16-2015
when I do
Code:
cat /proc/sys/kernel/shmmax

got
Code:
2458761

(kernel.shmmax parametre value. and Os is RHEL6
Last edited by stew; 04-16-2015 at 04:49 AM..
# 4  
Old 04-16-2015
So why are you using awk for either of these?

Code:
read x semmns < //proc/sys/kernel/sem
read shmmax < /proc/sys/kernel/shmmax
[ "$semmns" -lt 33000 ] && printf 'semmns: %d\n' "$semmns"
[ "$shmmax" -gt 200 ] && printf 'shmmax: %d\n' "$shmmax"

seems to do what you want.

If you insist on using awk and for some reason you don't want to do it the same way you checked SEMMNS (using $1 instead of $2), you could also try something like:
Code:
awk 'BEGIN{get line shmmax < "/proc/sys/kernel/shmmax"; if((shmmax + 0) > 200) print shmmax}'

Last edited by Don Cragun; 04-16-2015 at 05:19 AM.. Reason: Add +0 to guarantee numeric comparison and fix autospellcheck induced errors.
This User Gave Thanks to Don Cragun For This Post:
stew
# 5  
Old 04-16-2015
Thank you Smilie It worked. I guess get line should be "getline"

---------- Post updated at 04:31 AM ---------- Previous update was at 03:47 AM ----------

I have one more doubt, I ran below command the value
Code:
kernel.shmmax = 2458761

is added under /etc/sysctl.conf
Code:
 
 awk ' BEGIN{getline shmmax < "/proc/sys/kernel/shmmax"; if((shmmax + 0) > 200) print "kernel.shmmax = " shmmax}' >>/etc/sysctl.conf

In few servers" cat /proc/sys/kernel/shmma"x value would be already present in "/etc/sysctl.conf", in that case it should not add nedd to update the vlaue

Code:
 
"/usr/bin/awk ''BEGIN{getline shmmax < "/proc/sys/kernel/shmmax"; if((shmmax + 0) > 200) sub(existingvalue,shmmax}' >>/etc/sysctl.conf

want to substitute instead of new entry, is it possible
# 6  
Old 04-16-2015
When tampering with system parameters, you should know EXACTLY wha you are doing! So, please be very careful and make backups.
Try
Code:
awk     '
BEGIN                   {getline shmmax < "/proc/sys/kernel/shmmax"
                         if((shmmax + 0) > 200)
                        }
/^kernel.printk/        {$3 = shmmax
                         done=1
                        }
1
END                     {if (done) exit
                         print "kernel.shmmax = ", shmmax
                        }
        ' /etc/sysctl.conf

and, when happy, redirect the output to a temp file and mv it to the target, then.
# 7  
Old 04-16-2015
Quote:
Originally Posted by stew
Thank you Smilie It worked. I guess get line should be "getline"
Yes. I apologize. I installed a security update to my browser last weekend, and the spell checker is apparently much more aggressive at fixing (supposed) mistakes (even after I have told it not to change something I typed). For some reason it thought it should change shmmax to shammy and when I went back in to fix that, it silently also changed getline to get line. I'm going to have to watch it more closely (or disable it).

It looks like RudiC's suggestion was also mangled by something... The line he suggested:
Code:
/^kernel.printk/        {$3 = shmmax

should be:
Code:
/^kernel.shmmax/        {$3 = shmmax

This User Gave Thanks to Don Cragun For This Post:
RudiC
 
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