awk question

davidkline · 09-29-2006, 12:09 PM

I would like to use awk to extract the major device number from the file /proc/devices (first field) in a shell script. Something like this:

#!/bin/sh
number=32

major=$(..awk command using $number..)

I tried a few variations and I can't seem to get it to work. Does anyone know how to do this?

Please advise, thanks in advance,
/david

ygloo · 09-29-2006, 12:14 PM

major=$( cat /proc/devices | awk '{ print $1 }' )

druuna · 09-29-2006, 12:24 PM

Hi,

Code:

#!/bin/bash

number=128

awk -v NUMBER="$number" '$1 == NUMBER { print $0 }' /proc/devices

If I understand you correctly you want to use a variable, set in bash/sh, that is used in awk. You need to use awk's -v option (-v NUMBER="$number"). NUMBER can be anything you want and is used within awk, the $number part is the bash variable you 'give' to awk.

The above code snippet prints the entire line if there is a match (I don't have a 32, so I substituted it with 128).

Hope this helps.

davidkline · 09-29-2006, 01:01 PM

Thank you for your responses...

I'm sorry ... I don't think I worded the question correctly. What I'd like to do is to search the file /proc/devices for a specific device name specified by a variable and have awk (or maybe there is something better) return the device number. For example:

#!/bin/sh
device="mydriver"
major=$( ...awk command... )

Thanks in advance,

ygloo · 09-29-2006, 01:07 PM

#!/bin/sh
number=32

major=$( cat /proc/devices | grep $number | awk '{ print $1 }' )

druuna · 09-29-2006, 01:11 PM

Hi,

It takes just a few minor changes to my original code posted to do this:

Code:

#!/bin/bash

number="netlink"

awk -v number="$number" '$2 == number { print $1 }' /proc/devices

Sample run (script is called tets):

$ ./tets
36

This: 36 netlink is the line from /proc/devices,

If you don't want to use a script, you can use the following one-liner from the commandline:

awk '/netlink/ { print $1}' /proc/devices

Hope this helps.

davidkline · 09-29-2006, 01:14 PM

Thank you! This works great...

ygloo · 09-29-2006, 01:15 PM

awk '/$number/ { print $1}' /proc/devices

druuna · 09-29-2006, 01:32 PM

Hi,

@ygloo:

Quote:

Originally Posted by ygloo

awk '/$number/ { print $1}' /proc/devices

This will not work.

AWK does not substitute the content of the variable ($number) and there will be no hit/output:
$ number="netlink"
$ awk '/$number/ { print $1}' /proc/devices
$

ygloo · 09-29-2006, 01:37 PM

found a way to substitute variable within awk...
quote with '
awk '/'$number'/ { print $1}' /proc/devices

___________________________found it here:
http://www.shelldorado.com/