check variable content size in sh script

[Teske, Devin]

On May 16, 2013, at 9:27 AM, Teske, Devin wrote:


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.

I figured I'd help as many folks as I can…

http://svnweb.freebsd.org/base?view=revision&revision=250701

Added it to my string processing library. Lots of other useful functions in there.
--
Cheers,
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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