shell scripting

Posted on

I’ve been playing around with bash scripting quite a bit recently in relation to my current job.

Came up with one that’s really useful (imho) around chkconfig:

# mass set all services known to chkconfig to be `on` or `off` at given level
# written by warren myers - warren@warrenmyers.com
# 28 sep 2009

echo "USAGE:"
echo " $0 <level> [on|off]"
echo

# list all services, just the name, skip blank lines, do in order
SERVICES=`chkconfig --list | cut -f 1 | grep -v ^$ | grep -v ':' | sort`

for SERVICE in $SERVICES
do
  chkconfig --level $1 $SERVICE $2
  echo "$SERVICE has been altered for $1 to state $2"
done

Yes – there’s an evil you could perform:

for CS in `chkconfig --list | cut -f 1 | grep -v ^$ | grep -v ':'`
do
  chkconfig --level 12345 $CS off
done

So, if you wanted to stop all services from coming on at startup, you could – and not know you did it until you rebooted.

merikebi

5 thoughts on “shell scripting”

  1. Warren,

    just a style/good-practice recommendation:

    Instead of:
    SERVICES=`chkconfig –list | cut -f 1 | grep -v ^$ | grep -v ‘:’ | sort`

    Use:
    SERVICES=$(chkconfig –list | cut -f 1 | grep -v ^$ | grep -v ‘:’ | sort)

    It’s easier to read than the ticks. 😉

  2. Also, you might want to turn the usage message into a function. I do that all the time:

    ———- cut here ———–
    usage() {
    echo “usage: ${0##*/} [on|off]” >&2
    exit 1
    }

    # and then, some parameter checking
    [[ -z “$1” || -z “$2” ]] && usage
    [[ “$2” == “on” || “$2” == “off” ]] || usage
    ———- cut here ———–

  3. Thanks, @Alexei – I do typically do a usage of some kind, and of course checking your input is *always* a good idea =D

    Curious, though – why is the $() preferable to “ for grabbing the output of an exec’d command into the variable?

  4. Legibility. I work with UNIX for about 15 yrs now, shell-scripting probably the same. I *know* the ticks well enough. But every now and then, I still get caught in a messy sequence of ‘ and ” and `, mostly when they’re nested.

    Thus, replacing the backtick with $( ) makes things one degree less messy.

    IMHO, naturally 😉

Comments are closed.