expanding variable in shell script

dipenchaudhary · 02-07-2006, 03:19 PM

hii
i m new to shell scripting and i have a situation which i dont even know if is possible..
suppose i have a variable ... can i expand it to use to make another variable .. i suppsoe this shud be possible
for eg i m tryin to reverse the arguments supplied

#!/bin/bash
echo number of arguments are $#
a=1
while `test $a -le $#`
do
echo ${$a}
a=`expr $a + 1`
done

my problem is in echo line ... i m trying hit n trial to expand $a to a numeric ... and then refrencing the argument as we normally do.. like $1 , $2 and so on

so my question is can i use 2 $ sign ... obviously inner $ shud be expanded to its value ..

i wanna refer to $1 by assigning $a to another $ something like
$$a
where $a shud expand to some integer ... and $<integer> shud be my argument ..

plzz write back .. i m certainly new in scripting ...
thnks

satinet · 02-07-2006, 03:31 PM

dipen,

i am no beginner at shell scripting, but i really not clear what you are trying to do. maybe you can explain it a little more? sorry i'm sure others will agree. although its good that you are interesting in this...

Hko · 02-07-2006, 03:47 PM

I think I do understand.

Quote:

i wanna refer to $1 by assigning $a to another $ something like
$$a
where $a shud expand to some integer ... and $<integer> shud be my argument ..

Change the "echo line" to:

Code:

echo ${!a}

But in bash the script can be done simpler so you don't need to get the number from $a:

Code:

#!/bin/bash
echo Number of arguments = $#
echo $1
while shift ; do
	echo $1
done

dipenchaudhary · 02-08-2006, 07:39 AM

kooool Hko
hurray it worked ....please give me a link to some good tutorial on shell script or some book which i can get from college library ..which explains such interesting stuffs

sorry satinet ... but i really write messed up english .. i have been pointed out a lot mant times of LQ .. i will try to improve !! satinet plzz suggest some good book or link to shell scripting

thnk u guys ... i will come back with other silly doubts
thnks again

dipenchaudhary · 02-08-2006, 07:40 AM

kooool Hko
hurray it worked ....please give me a link to some good tutorial on shell script or some book which i can get from college library ..which explains such interesting stuffs

sorry satinet ... but i really write messed up english .. i have been pointed out a lot mant times on LQ .. i will try to improve !! satinet plzz suggest some good book or link to shell scripting

thnk u guys ... i will come back with other silly doubts
thnks again

dipenchaudhary · 02-08-2006, 07:58 AM

and yehh hko .. wot does shift (after while) do in this script ..by the way we had to print in reverse .. n this script print in the same order as supplied .. i tried to change
#!/bin/bash
echo Number of arguments = $#
echo ${!#}
while shift ; do
echo ${!#}
done

output : last argument

then i tried ...
#!/bin/bash
echo Number of arguments = $#
echo ${!#}
while shift -1 ; do
echo ${!#}
done

output : wu , syntax error

can u give me link to some good book or tutorial .. or refer some good book? i really need it .. i m willin to spend time
thnks in advance

satinet · 02-08-2006, 08:19 AM

there is a good book called 'classic shell scripting' that is pretty good (IMHO) from O'Reilly. They also do a SED and awk book.

There are a few online tutorials, anyone recommend them? I'll get back to you on this...

satinet · 02-08-2006, 10:24 AM

i just saw this:

http://www.cactus.org/~dak/shellscript.html

Hko · 02-08-2006, 05:05 PM

http://www.tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html
http://www.tldp.org/LDP/abs/html/index.html