if statement in a for loop

dsmith8890 · 05-30-2012, 08:22 AM

HI im trying to run this loop so that it will only ask the user to enter his details 3 times before it exits the program if the details are incorect. I have managed to use a while loop, but this does not achieve exactly what im after! does anyone have any ideas. Just to clarify im using Bash Unix.

Thanks

Code:

#!/bin/bash

while :
do
echo "please enter you username"
read user
grep -iq "^user" usernames
a=$?
echo "please enter your password"
read pass
grep -i "^$user" usernames | grep -q "$pass$"
b=$?

if [ $a -eq 0 -a $b -eq 0 ]
then
echo "welcome"
break
else
echo "please try again"
fi
done

dsmith8890 · 05-30-2012, 08:46 AM

is this even possible? sorry but i am new to this!!

grail · 05-30-2012, 09:25 AM

Why not just use a counter and have the while loop test if correct or a count of 3?

Are we to understand that you have a plain text file containing user names and passwords (not very safe by the way)?

dsmith8890 · 05-30-2012, 10:07 AM

Thanks that seems to work. Your right, although it doesnt actually hold the correct passwords its only a sample programe as im just practicing.

grail · 05-30-2012, 12:53 PM

Quote:

Your right, although it doesnt actually hold the correct passwords its only a sample programe as im just practicing.

No problem ... just a warning

If you have solved your problem, please use the thread tools to mark it as such.

tuxdev · 05-30-2012, 03:51 PM

What are you trying to accomplish here? Asking a user for their password in bash itself is *very* scary.

David the H. · 05-31-2012, 01:29 AM

I don't think it's that bad if, for example, it's a wrapper script for a command that uses a password anyway. The values aren't available outside of the script's process,and when it terminates they will be lost. More worrisome is storing them in a plain text file, as has already been mentioned.

If I may give a bit of general advice for our new scripter, however...

1)
Clean, consistent formatting makes code readable and more easily debuggable. Indent all your sub-commands, and separate logical sections with whitespace. Add comments anywhere the code isn't completely obvious (and remember, what seems obvious to you now will not be so a year or so down the line).

Many people also feel that it's more readable to place the "do/then" keywords on the same line as the "for/while/until/if" keywords, as it more clearly separates the outside block from the inside block.

Code:

for var in fee fai foo fum ; do

	if [[ "$var" == "foo" ]]; then
		echo "Found 'foo'."
	fi

done

2)
When using bash or ksh, it's recommended to use ((..)) for numerical tests, and [[..]] for string/file tests and complex expressions. Avoid using the old [..] test unless you specifically need POSIX-style portability.

http://mywiki.wooledge.org/ArithmeticExpression
http://mywiki.wooledge.org/BashFAQ/031
http://wiki.bash-hackers.org/commands/classictest
http://wiki.bash-hackers.org/syntax/...nal_expression

Otherwise, it's looking pretty good.