How to make a bash script ask for a specific key.

Slightly Disoriented · 11-21-2010, 03:02 PM

I am attempting to learn how write bash scripts. I want one to ask for a specific key. For example, I want it to ask a question, then if it is like, y for yes, or n for no, it does a specific thing. I'm thinking it would be something like:

Code:

#!/bin/bash
echo "Are you a boy? y/n"
read -t3

then something... Please help!

Slightly Disoriented · 11-21-2010, 04:11 PM

Oh, I wasn't really clear. I want it to, if possible, do a certain command if a certain key is pressed. Like, in the above script, if they pressed n then it would

Code:

echo "So you are a girl.

and if y then it would do something like

Code:

echo "Thats what I thought.

I know

Code:

if

would be used. I can not find it on google.

sycamorex · 11-21-2010, 04:36 PM

This should get you started.
http://tldp.org/LDP/Bash-Beginners-G...ect_07_01.html

and this:
http://www.tech-recipes.com/rx/209/b...ng-comparison/

Slightly Disoriented · 11-21-2010, 05:04 PM

Hmmm, well the way those made it look like it would be

Code:

#!/bin/bash
echo "Yes or No (Y/N)"
read $var
if [$var = "y" ]
then 
	echo "Yes"
else
	echo "No"
fi
echo "Done"
exit

But when I run that script, here's what comes back:

Code:

~$ cd Linux/Scripts && bash Response.sh && cd
Yes or No (Y/N)
y
Response.sh: line 4: [: =: unary operator expected
No
Done

I don't exactly get those sites... Keep in mind, I'm just starting, and I don't really have any other programming experience. Sorry, but do you what I need to do?

pwc101 · 11-21-2010, 05:07 PM

Quote:

Originally Posted by Slightly Disoriented

Hmmm, well the way those made it look like it would be

Code:

#!/bin/bash
echo "Yes or No (Y/N)"
read $var
if [$var = "y" ]
then 
	echo "Yes"
else
	echo "No"
fi
echo "Done"
exit

But when I run that script, here's what comes back:

Code:

~$ cd Linux/Scripts && bash Response.sh && cd
Yes or No (Y/N)
y
Response.sh: line 4: [: =: unary operator expected
No
Done

I don't exactly get those sites... Keep in mind, I'm just starting, and I don't really have any other programming experience. Sorry, but do you what I need to do?

You need a space between [ and $var:

Code:

if [ $var = "y" ]

[ is actually a command, so just like ls or cd, you separate it from its arguments with a space.

Dark_Helmet · 11-21-2010, 05:15 PM

Quote:

Code:

read $var

That line also needs to be changed. It should not have the $ in front of the variable. So, it should be:

Code:

read var

Explanation:
The $ tells the shell that you want to substitute the value of the variable in place of the variable's name. You do not use the $ when using a statement that stores a value in the variable. For instance "var=1" or (as above) storing a user's input into the variable.

Slightly Disoriented · 11-21-2010, 05:23 PM

Mmmm, neither worked. At one point it worked without returning errors with:

Code:

read $var
if [ : var =  "y" ]

But it acted like I didn't press the y key and just went to else.... And when I take out the $ and : it returned the same thing, I also tried removing the "" marks. I though the $ was there to declare that it was a variable, I didn't know I just reconized that it was one.

sycamorex · 11-21-2010, 05:27 PM

It should work. Just remove the dollar sign from "read $var" and make sure there's a space in
if [ $var = "y" ]

Can you post the code as it looks now?

Slightly Disoriented · 11-21-2010, 05:27 PM

Aha! It worked, I only had to take out the $ infront of var in the

Code:

read

line, not the

Code:

if

line. It looked like:

Code:

#!/bin/bash
echo "Yes or No (Y/N)"
read var
if [ $var =  "y" ]
then 
	echo "Yes"
else
	echo "No"
fi
echo "Done"
exit

Now 1 more thing... Is there a way to have more than one if. Like

Code:

echo "Pick a number, 1, 2, 3)
read var
if [ $var = 1 ]
then
echo "You picked 1"

But then have one for 2 and 3.
Thank you for all the help.

sycamorex · 11-21-2010, 05:30 PM

You might want to look at Bash's case statement. It'll be more appropriate in this case.

Slightly Disoriented · 11-21-2010, 05:34 PM

@Sycamorex What do you mean Bash's case statment.

barriehie · 11-21-2010, 05:37 PM

Here's a link to a bash scripting guide. Don't be put off by the title.

http://tldp.org/LDP/abs/html/

sycamorex · 11-21-2010, 05:40 PM

Quote:

Originally Posted by Slightly Disoriented

@Sycamorex What do you mean Bash's case statment.

http://www.tech-recipes.com/rx/212/b...ase_statement/

ee437 · 11-22-2010, 09:49 AM

looking over your script, without checking in detail, you do need

if [ $var == "y" ] ;

i'm sure you need two ='s, and you probably also need the semicolon ';'.

with only one = sign, it sets var to y, and does not compare.

and, the case statement is very convenient...

i hope that helps.

pwc101 · 11-22-2010, 10:27 AM

Quote:

Originally Posted by ee437

looking over your script, without checking in detail, you do need

if [ $var == "y" ] ;

with only one = sign, it sets var to y, and does not compare.

Did you test your assertion?

When using [, testing if two strings match is performed with =. When using [[, then you need ==. See http://unixhelp.ed.ac.uk/CGI/man-cgi?test.

Quote:

Originally Posted by ee437

and you probably also need the semicolon ';'.

This is only true if you don't put the then on a new line.