check variable content size in sh script

[Teske, Devin]

On May 16, 2013, at 9:06 AM, Teske, Devin wrote:

> 
> On May 16, 2013, at 8:28 AM, Tim Daneliuk wrote:
> 
>> On 05/16/2013 10:08 AM, Joe wrote:
>>> Hello
>>> 
>>> Have script that has max size on content in a variable.
>>> How to code size less than 51 characters?
>>> 
>> 
>> FOO="Some string you want to check length of"
>> FOOLEN=`echo $FOO | wc | awk '{print $3}'`
>> 
> 
> Uh, without forking to 2 separate programs…
> 
> FOOLEN=${#FOO}
> 
> 
>> You can then use $FOOLEN in a conditional.
>> 
> 
> 
> However, if the OP wanted to actually truncate $FOO to 51 characters:
> 
> 
> NEWFOO=$( echo "$FOO" | awk -v max=51 '{print substr($0,0,max)}' )
> 
> 
> However, if you want to handle the case of $FOO containing newlines (and you want the newline to count toward the max), then this instead would do the trick:
> 
> 
> NEWFOO=$( echo "$FOO" | awk -v max=51 '
> 	{
> 		len = length($0)
> 		max -= len
> 		print substr($0,0,(max > 0 ? len : max + len))
> 		if ( max < 0 ) exit
> 		max--
> 	}' )
> 

For fun, I decided to expand on the solution I provided immediately above… turning it into a function that you might be a little more familiar with:

snprintf()
{
        local __var_to_set="$1" __size="$2"
        shift 2 # var_to_set/size
        eval "$__var_to_set"=\$\( printf \"\$@\" \| awk -v max=\"\$__size\" \''
        {
                len = length($0)
                max -= len
                print substr($0,0,(max > 0 ? len : max + len))
                if ( max < 0 ) exit
                max--
        }'\' \)
}

Example usage:

FOO=$( printf "abc\n123\n" )
snprintf NEWFOO 6 "%s" "$FOO"
echo "NEWFOO=[$NEWFOO] len=[${#NEWFOO}]"

Produces:

NEWFOO=[abc
12] len=[6]

Hopefully this should help some folks.
-- 
Devin



> 
> $NEWFOO, even if multi-line, will be limited to 51-bytes (adjust max=51 accordingly for other desired-lengths). Newlines are preserved.
> 
> Last, but not least, if you want to be able to handle multi-line values but only want to return the first line up-to N bytes (using 51 as the OP used):
> 
> 
> NEWFOO=$( echo "$FOO" | awk -v max=51 '{ print substr($0,0,max); exit }' )
> 
> 
> If $FOO had multiple lines, $NEWFOO will have only the first line (and it will be truncated to 51 bytes or less).
> -- 
> Devin

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