I am trying to understand the concept of positional parameters.
I do understand that positional parameters:
1. Are initialized by shell
2. Have a max of 9 parameters ($1 to $9)
3. Have no limit on the number of arguments
4. Can be rearranged with the shift command
Can someone please give me a simple example to help me better understand how to use positional parameters?
1. Are initialized by shell
They are not initialized by the shell. Rather they pick up the values from the arguments passed to a shell script.
2. Have a max of 9 parameters ($1 to $9)
Not true. It can go beyond 9. After $9, the next positional parameter will be accessed as ${10}, ${11} .. et al.
3. Have no limit on the number of arguments
This is true. Bit this statement is contradicting to what you mentioned in point 2.
4. Can be rearranged with the shift command
The postional arguments gets shifted one place to the left when you make one shift call. i.e. $1 will get the value that was held by $2, $2 will get the value that was held by $3.. so on and so forth..
$0 never gets shifted.
And positional parameters cant be assigned new values unless you use set
1. Are initialized by shell
They are not initialized by the shell. Rather they pick up the values from the arguments passed to a shell script.
I am not sure I completely understand this.
For example, if I do the following:
Code:
$> var1=one
$> var2=two
$> var3=three
$> echo $var1
one
$> echo $var2
two
$> echo $var3
three
How am I able to use these variables from a file within a different directory?
Is this a good example that will help me understand the concept? I am trying to write a few small examples to help me see exactly what is happening.
Code:
2. Have a max of 9 parameters ($1 to $9)
Not true. It can go beyond 9. After $9, the next positional parameter will be accessed as ${10}, ${11} .. et al.
What about addressable parameters? Is it a max of 9 addressable parameters? I am not sure where I read this. I wrote it down as I was trying to learn more about it.
Code:
3. Have no limit on the number of arguments
This is true. Bit this statement is contradicting to what you mentioned in point 2.
I understand that this does contradict what I originally posted for #2.
Code:
4. Can be rearranged with the shift command
The postional arguments gets shifted one place to the left when you make one shift call. i.e. $1 will get the value that was held by $2, $2 will get the value that was held by $3.. so on and so forth..
$0 never gets shifted.
The Bourne shell does not support ${10}. Here is an example where I tried it:
Code:
$ set one two three four five six seven eight nine ten eleven
$ echo $1
one
$ echo ${1}
one
$ echo $9
nine
$ echo ${10}
bad substitution
$ shift
$ echo $9
ten
$
The Korn shell and Bash both do support it. But not the old Bourne shell. The Bourne shell is very old. Replacements have been available since at least 1988. I don't understand why people would use it for new scripts. The Posix standard mandates a newer shell. Any version of Unix that does not have a modern shell available is in violation of the standard.
OK, after reading the linked lesson (Lesson 13: Positional Parameters), I have written a test program. This program is called "positional_parameters":
Code:
set -vx
set
echo "Positional Parameters"
# The following commented lines do not work.
# Is it because I am using the Bourne Shell?
# if["$1"!=""];
# then echo "Positional parameter 1 contains something."
# else echo "Positional parameter 1 is empty."
# fi
# if[ $# -gt 0 ]; then
# echo "Your command line contains $# arguments"
# else echo "Your command line contains no arguments"
# fi
echo '$0 = ' $0
echo '$1 = ' $1
echo '$2 = ' $2
echo '$3 = ' $3
banner $1 $2 $3
banner "$1 $2 $3"
banner "$*"
banner "$@"
# mailtolist=someName@someDomain.com
mailtolist=someName@someDomain.com
mail mailtolist < testing
set +vx
The following are the contents of the "testing" file:
Code:
banner testing
banner 1 2 3 4
I am getting the following error when I run the positional_parameters program:
Code:
mailtolist... User unknown
Am I not initializing it correctly?
Is it possible for the mailtolist variable to contain more than one e-mail address?
I would like to try to invoke the positional_parameters program from the command line and send the contents of my testing file to my e-mail address.
Would this be the correct command?
Code:
$> positional_parameters testing
Do I need to export mailtolist?
Do I need to use command substitution to test it?
I appreciate the feedback. I am enjoying what I am learning so far.
Thank you,
Eric
Last edited by ericelysia; 10-22-2005 at 12:05 PM..
I am trying to code an if statement that accepts two parameters and see if those parameters are in another file called teledir.txt. If it already exists in the file, it is to say "Entry Exists". If not, I add it to the file and say "Entry Added". This is the code I have so far:
if ; then
... (1 Reply)
I'm new with 'sed' and for sure something still I don't understand yet with it. If you see my output on ">Output..." portion, the new directory still on "source_dir" instead of "dest_dir". You may disregard for the "tar" part, this is just a test script, just for me to understand 'sed' using the... (3 Replies)
I like to “optimize” / make more like a real program my bash script by replacing repetitious code which utilizes positional parameters.
I am having two issues I cannot solve and would appreciate some assistance with resolving them.
a) how to modify the whiptail checklist... (3 Replies)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
STEP 1: Create a Bash shell script (myscript) inside the a2 directory. The script should allow the user to pass... (3 Replies)
In a Bash script I used getopts command to let a user does something regards to the selected options. The question is: How do you find out what is the name of the file that user inserted in the command line like the following:
The good part is this file is always the last argument in the... (2 Replies)
Hi all,
I have one small requirment...
I have prepared one script. we have to pass two possitional parameters to the script. What I want to do is if the parameters are not passed then i dont want the script to start the process...
For ex:
$ ./a.sh parm1 parm2
#Here, it can start... (7 Replies)
Hi,
Can any one provide the Unix command to reset the positional parameters?
Please see the below example where i have to pass 2 parameters to Shell1.sh.
Step1) . ./Shell1.sh 2 3
successfully executed, Then i executed(next step only) the same shell script again,this time no... (4 Replies)
I need to get file names from commandline arguments, it may be any no of arguements, Using for loop i got but how do i display it, bcoz $i will give the number i is assigned $$i is not working either $($i), i need the names of the files got in the arguement (2 Replies)
HPUX11.0/Korn Shell
I have an old script that takes in a series of arguments when its called. The script is really more of a common set of functions that gets called by other scripts as needed. I have been asked to make this into a menu driven script to rollout to app support for their use during... (2 Replies)