UNIX for Dummies Questions & Answers

Hi,

I have a requirement wherein, I need to validate a user input of the numbers that are comma separated.
E.g . The input should be in the format 1,2,3...n (count of numbers is not known) . The user has to mention the input in this format, else it should exit from the program.
Please let me know how effectively we can handle this.
TIA

You're not clear what this is for...
Are you talking about a command line utility? Or are you talking about a C program?

A simple awk script could do this if you're just validating an input file before doing something else.

I'm not the world's greatest authority on awk, as i tend to think of processing lines like I would in C, but this might help you.

#!/bin/awk

{ last=$1
for (i=2; i<NF; i++) {
if ($i < last)
exit NR
last=$i
}

This will return an exit code matching the first wrong line, or zero if everything is OK for all lines of the input.

HTH

Code:

> echo "1,2,3,4" | tr -d "[:digit:]|,"

> echo "1,2,3,4,a" | tr -d "[:digit:]|,"
a

The first example returns nothing, while the second returns the letter 'a' -- the bad character according to my understanding of your request. The result of these commands could be set to a variable and/or simply analyzed to see if something 'fell thru' the command (and thus a bad character).

Hi,

I guess the requirement is not clear. Let me give you more description.

Firstly, I am expecting a regular expression in UNIX.

The script reads the column positions using "read col".Now when prompted to provide the values, the user should enter the required field no.'s of a file in the format 1,3,4,..n (no. of fields that a user enters is not known).
As the column no.'s should b only numbers and cannot contain any non-numeric input, the patterns like 1,a,3 or 1,4,b..or with any other special characters needs to be rejected.
I can validate the input for 2 numbers, using the regular expression
"^[0-9],[0-9]$". But, couldn't make this work for n(unknown count) of numbers.
Please let me know, how we can resolve this.

TIA

if you have Python, here's an alternative

Code:

#!/usr/bin/env python
numbers = raw_input("Enter field numbers with commas (1,3,4): ")
try:
    map(int,numbers.split(","))    
except Exception,e:
    print "Error in input, not a number: ",e
else:
    print "Ok"

output:

Code:

# ./test.py
Enter field numbers with commas (1,3,4): 1,2,3
Ok
# ./test.py
Enter field numbers with commas (1,3,4): 1,2,a
Error in input, not a number:  invalid literal for int(): a

Thankyou.

But it would have been gr8 if we had such solution on UNIX also