Setting Integer Variables in Bash

Setting Integer Variables in Bash

[whitewall]

The text below is from a text file.  If I type the commands line-by-line in
the bash then the commands work as expected.  If I save the commands in a
text file and call the script I get the error message:
': not a valid identifier2: declare: 'Red
': not a valid identifier3: declare: 'Green

#! /cygdrive/c/cygwin/bin/bash
declare -i Red
declare -i Green
Red=10
Green=$Red+1
echo $Green
exit 0
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Re: Setting Integer Variables in Bash

[Tim McDaniel]

On Thu, 29 Jan 2009, whitewall <thewhitewall@live.co.uk> wrote:
> The text below is from a text file.  If I type the commands
> line-by-line in the bash then the commands work as expected.  If I
> save the commands in a text file and call the script I get the error
> message:
> ': not a valid identifier2: declare: 'Red
> ': not a valid identifier3: declare: 'Green

Two error messages.

> #! /cygdrive/c/cygwin/bin/bash
> declare -i Red
> declare -i Green
> Red=10
> Green=$Red+1
> echo $Green
> exit 0

You have a carriage return at the end of each line.  bash does NOT
consider carriage return to be whitespace, dammit, so it is considered
normal characters.  So it things, for example, that you're declaring a
variable named "Red\r", a four-character name, and it just doesn't
allow carriage return in the variable name.

The key to recognizing the situation is to see
     ': not a valid identifier2: declare: 'Red
and recognize that there's a carriage return in the middle of the
message.  The opening ' is just before Red.  Its matching closing ' is
shown as the start of the line -- because carriage return causes the
output display to return to the start of line.

So
- by default, created files in UNIX file format, not native Windows.
- strip out the carriage returns from your existing script

-- 
Tim McDaniel, tmcd@panix.com

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Re: Setting Integer Variables in Bash

[Mark J. Reed]

On Thu, Jan 29, 2009 at 5:54 PM, whitewall wrote:
>
> The text below is from a text file.  If I type the commands line-by-line in
> the bash then the commands work as expected.  If I save the commands in a
> text file and call the script I get the error message:
> ': not a valid identifier2: declare: 'Red
> ': not a valid identifier3: declare: 'Green

If you run the script's stderr through od or similar, you will see
that what bash is really saying is

 /path/to/your/file: line 2: declare: 'Red\r': not a valid identifier
 /path/to/your/file: line 3: declare: 'Green\r': not a valid identifier

where the '\r's are carriage returns which cause the cursor to go back
and overwrite the first part of  the message.
Run d2u on your script.

> #! /cygdrive/c/cygwin/bin/bash
> declare -i Red
> declare -i Green
> Red=10
> Green=$Red+1

Since you've declared both Green and Red as integer, you should just
do Green=Red+1, without the dollar sign. Doing Green=$Red+1 first
takes Red's value, which is stored as an integer, expands it back into
its decimal string representation, and then reparses it to yield its
integer value.  I know that in a real script, any efficiency gains
will be swamped by I/O, but there's no sense making the shell do extra
work. :)

-- 
Mark J. Reed <markjreed@gmail.com>

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Re: Setting Integer Variables in Bash

[Tim McDaniel]

On Thu, 29 Jan 2009, Mark J. Reed wrote:
> On Thu, Jan 29, 2009 at 5:54 PM, whitewall wrote:
>> #! /cygdrive/c/cygwin/bin/bash
>> declare -i Red
>> declare -i Green
>> Red=10
>> Green=$Red+1
>
> Since you've declared both Green and Red as integer, you should just
> do Green=Red+1, without the dollar sign. Doing Green=$Red+1 first
> takes Red's value, which is stored as an integer, expands it back
> into its decimal string representation, and then reparses it to
> yield its integer value.

There IS one subtle difference.  If you're running with "set -x",
     Green=$Red+1
will echo
     + Green=10+1
But
     Green=Red+1
will echo
     + Green=Red+1
(assuming that you've not changed PS4, IFS, &c &c).  You can decide
which "set -x" output you like.  I found that I preferred the
substituted forms, the ones with $this and $that.

-- 
Tim McDaniel, tmcd@panix.com

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