Positional Parameters Shell Scripting

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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 a 3 digit number to this script when it runs. Make sure that the parameter/argument entered by the user consists of exactly 3 numbers. If it�s not 3 numbers, then give an appropriate error message and exit with appropriate exit status. If the parameter entered was a 3 digit number, then display it.
This script should create a subdirectory called �numbers� inside the a2 directory. If that directory already exists, it should delete the existing one and create a new one.
The script should check the numbers and determine whether they are unique. For example, if the numbers passed to this script are 123, the script should create file1, file2 and file3 (inside the �numbers� directory). If last 3 digits are 121, then create file1 and file2. Your script should now list the files you have created.

2. Relevant commands, code, scripts, algorithms:

STEP 2: The script should now check for the existence of the �products� file in a2 directory. If it does not find that file, it should give an error message and exit. If the file does exist, it should display the contents of the file. Then it should cut the 2nd field (product name) from each line of the file (hint: use the cut command and use comma as the delimiter to pick the 2nd field). Capture the product names that are being cut into a separate file �names�. Then display the contents of this file �names�. Now the script should use the appropriate command to count the number of lines in the �names� file and display a message indicating how many products there are in the products file. For example, if you had 6 products in your products file, this message should say �I have 6 products in my product file� by using the number it obtained from counting the lines.

3. The attempts at a solution (include all code and scripts):

#!/bin/bash

input=$1
first=${input:0:1}
second=${input:0:1}
third=${input:2:1}


echo -n "Please enter 3 digits:"


if ! [[ $1 =~ ^[0-9][0-9][0-9]$ ]]; then
echo "PLEASE ENTER 3 DIGITS!"
fi

4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):

Seneca, Toronto, Canada, Lloyd, ULI101

Note: Without school/professor/course information, you will be banned if you post here! You must complete the entire template (not just parts of it).

I think you're a bit confused on the idea of positional parameters. They're the ones you get when you run the script, like ./myscript.sh 999

$1 would be 999 in that situation.

Your script looks mostly okay actually. You've got the correct syntax for if, which is a bit tricky. Though =~ only works in BASH or really new KSH. case ought to work everywhere.

case "$1" in
[0-9][0-9][0-9])
        # Do nothing
        ;;
*)
        echo "Not three digits"
        exit 1
        ;;
esac

As for how to check for the existence of files, that's another if, like if [[ -d "foldername" ]] See Test Operators for details on this and more flags.

Hi, I have the same assignment/course. For checking if its 3 digits, I have this output but it doesn't work.

if [ $num = ^[0-9][0-9][0-9]$ ]
then
echo $num
else
echo "Number not 3 digits"
fi

It always goes to the "else" result no matter what number I give (3, 33, 333). What am I doing wrong there? Thanks.

The test and [ ... ] commands' = operator performs a string comparison, not a pattern match.