Mama i am coming home..

Some times mama maynot be back home to receive you ,in that case you become a zombie .Mama need to call wait to make sure all the kids are back.

%cat checkzombie.sh
#!/bin/bash

./zombie1 &
./zombie
wait
%cat zombie1
#!/bin/bash

sleep 60
%cat zombie
#!/bin/bash

sleep 2


If you dont call wait at the end,the script will return before zombie1 is done as
zombie was executed as a background job.

Job Control

Job control lets you suspend _lot of jobs and then bring them into foreground.
Ctrl-Z takes the job into background...
But you can get it back by 'fg %n' where n is the ID of the job.

$ jobs
[1]- Stopped ./trace.sh
[2]+ Stopped ./trace.sh
$ fg %2
Coming soon are the traps in bash..beware..:)

A text browser with links --dump

This browser implemets quit (q) , back (b) and url.And a hidden command called 'd' which dumps history.More importantly i use the bash arrays.On L.H.S its HISTORY[$i] where as on R.H.S its ${HISTORY[$i]} and the length of array is ${#HISTORY[@]}...

#!/bin/bash
HISTORY=()
BACKINDEX=0

function updatehistory() {
    numvalues=${#HISTORY[@]}
    if (( $numvalues < 3 ))
        then
            HISTORY[$numvalues]=$1
        else
                    index=$(( numvalues -1))
            for (( i=0;i<$index;i++))
            do
                         j=$(( i+1))
                     HISTORY[$i]=${HISTORY[$j]}
                    done
                    i=$(( i++))
                HISTORY[$i]=$1
            fi
}



function dump_history(){

numvalues=${#HISTORY[@]}

        for (( i=0; i < $numvalues; i++))
        do
                    echo ${HISTORY[$i]}
        done
  }

while true
do
        echo "Enter a url.q for quit and b for back"
        read choice

        case $choice in

            q) exit ;;

            b) BACKINDEX=$(( BACKINDEX+1))
            numvalues=${#HISTORY[@]}
              INDEX=$(( numvalues - BACKINDEX -1 ))
              links  -http-proxy proxyserver:8088  -dump ${HISTORY[$INDEX]}
              ;;

            d) dump_history;;

            *) links  -http-proxy proxyserver:8088  -dump $choice
                        if ((  $? == 0 ))
                then
                    updatehistory $choice
                        fi
                        BACKINDEX=0
                        ;;
        esac

done

Counting lines with grep

Interesting option called -c , which lets you suppress output and oonly print the count of lines that matched so here is a replacement for "wc -l".

%cat bajajautofinance |grep -c ^.*$
11
%cat bajajautofinance |wc -l
11

A menu based bash directory browser

This could be useful when you have long pathnames to browse around and these pathnames have similar names...so CDPATH may not work.

#!/bin/bash

function cd()
{
if [ -z "$1" ]
then
    pushd $HOME
    return 0
fi
THEDIR=$(echo $1|sed -e "s/\~/$(echo $HOME|sed -e 's/\//\\\//g')/g")
pushd $THEDIR >/dev/null 2>&1


}

function lsd()
{
if [ -z "$1" ]
then
    select mydir in $(dirs -v|awk '{print $2}'|sort -u)
        do
        cd $mydir
        break
        done
else
        if [ -d "$1" ]
        then
            select mydir in $(find $1 -type d)
                do
                    cd $mydir
                    break
        done
    fi

fi

}

Blocks and IO

{

echo "Hello World"

echo "Bye World"

} > output.txt


And here is some bad news..Daniel Robbins(Gentoo Founder) joins MS...isn't that cheap ;)

Basic usage of select

Select creates a menu for you and its very simple to use.Here is an example

#cat select.sh
select test
do
echo $test
done
#./select.sh item1 item2 item3
1) item1
2) item2
3) item3
#? 2
item2
1) item1
2) item2
3) item3

Also this creates an infinite loop...so you need a break :)

Using eval

Here is some recursive(?) cool usage of eval.Thanks to Chandra..

$p=i
$i=1
$CM1=World
$CM=Hello
$eval HOST=\$CM\$$p
$echo $HOST
Hello1
$eval HOST=$CM\$CM$i
$echo $HOST
HelloWorld
$eval HOST=\$CM$i
$echo $HOST
World

Bash string operators

#!/bin/bash

while read foo
do
echo ${foo%%:*}
case ${foo%%:*} in
cm1*) export CM1=${foo##*:};;
esac

done < config.txt

echo $CM1

And the config.txt has syntax like
tunnel_port : 9999

Enjoy :)

Alternative for loop syntax

for(( i=1;i<6;i++))
do
echo $i
done