how to change from '-' to '_' (underscore)

[packet]

Hello All,

How to change from '-' to '_' in a file name below is my piece of code

#!/bash/sh

MC=goal
vardate=`date +%F`
vartime=`date +%H-%M-%S`

totalfilename="`$MC-$vardate-$vartime`"

echo "my file name is = $totalfilename"

the output is = goal-2008-10-31-11-22-32

I need the following output format

goal_2008-10-31_11-22-32

I want '_' underscore to separate only 3 fields

I tried to put '_' underscore after $MC and $vardate and $vartime
but it is not given expected output.

Help me out
Thanks in advance

[wje_lf]

You need to do three things with your script.

1. Unless you're running on a highly unusual system, the very first line is incorrect:
   

   #!/bash/sh

   Try running one of these commands at the shell prompt:
   

   which bash
   which sh

   to figure out what to put after the #!.
2. It is permissible to use an underscore character as part of a variable name. So when you refer to $MC_, bash will look for a variable named MC_, which you haven't defined. Instead, use ${MC}_ to separate your intended variable name from the following underscore.
3. When you assign values to variables vardate and vartime, you correctly use the backtick (`) to take an expression, use it as a command, and take the result of that command and use it in your command line. In both of these cases, that command is the date command.
   
   But then you also use the backtick in your assignment to the variable totalfilename. Why is this? Do you really want to run a command like
   

   goal_2008-10-31_00-12-48

   and take the output from that command and assign it to the variable totalfilename?

[burschik]

below is my piece of code

This is your code, is it? Well, since you are putting the "-" there in the first place, I would suggest that you simply stop doing that.

[wje_lf]

burschik, I don't quite understand your response. Removing the hyphens from his script is not going to get the underscores to work.

[ghostdog74]

i think he means this

totalfilename="`$MC-$vardate-$vartime`"

it can be this in the first place

totalfilename="`$MC_$vardate_$vartime`"

[wje_lf]

No, it can't, for reason number 2 and reason number 3 in my previous post.

[packet]

Hello All ,

I done a mistake in the code

totalfilename="`$MC-$vardate-$vartime`"


this as to be

totalfilename="$MC-$vardate-$vartime"

and the solution given by wje_lf is correct that is I need to { } to MC i.e the following line is correct that what i need

totalfilename="${MC}_${vardate}_${vartime}"

the output will come as

goal_2008-10-31_00-12-48


thanks lot

[burschik]

burschik, I don't quite understand your response. Removing the hyphens from his script is not going to get the underscores to work.

Well, no, it wouldn't. I did not realize the original poster does not understand variable naming. The bash syntax for parameter expansion is ${var}. One should not use shortcuts unless one understands how they work. In light of this new information, my reply would be:

date +'goal_%F_%H-%M-%S'