Csdrhrt

I have this variables

start=$1;

end=$2;

sn=${#start}

en=${#end}

and this if :

if ( [ $# -eq 2 ] )

then

elif ( [ $sn -ne 3 ] && [ -n "$(printf '%sn' "$start" | sed 's/[0-9]//g') " ] );

then     

    echo "Incorrect format"

    exit 1

elif ( [ $en -ne 3 ] && [ -n "$(printf '%sn' "$end" | sed 's/[0-9]//g') " ] );

then

    echo "Incorrect format"

    exit 1

else

    echo "Correct format"

    exit 1

fi

and I get unexpected at the first elif , I want to check the arguments provided by the user and they have to be made by only 3 digits .

if ( [ $# -eq 2 ] )

then

elif

As Jeff's answer says, the first if condition is missing the part with the commands. The error messages given by Bash and Dash are a bit vague, it seems like they come directly from the parser, and they haven't bothered to add a more user-friendly message there.

If you don't want to do anything inside a branch, you'll still need to add some command there. I'd suggest true, which doesn't do anything.

Fixing that, shellcheck.net gives a couple of more observations:

if ( [ $# -eq 2 ] )

   ^-- SC2233: Remove superfluous (..) around condition.

The parenthesis start a subshell, which is not necessary here (and involves extra overhead, like forking a subprocess in Bash).

... [ -n "$(printf '%sn' "$start" | sed 's/[0-9]//g') " ] 

>>                                                    ^-- 

             SC2157: Argument to -n is always true due to literal strings.

You've quoted the command substitution, good! But you have an extra space there in the end. Whatever the command substitution outputs, the argument to -n will never be empty, because of that space.

(It also notes about quoting $sn and $en, which would be the careful thing to do, but isn't really necessary if you know IFS doesn't contain any digits.)

That said, I'm not sure the conditions still are quite right. You say:

I want to check the arguments provided by the user and they have to be made by only 3 digits .

But note that the test below catches only the case where sn is not three, and in addition there are other characters than numbers, i.e. it passes abc and 1234, and only rejects, say abcd. You want an or condition, ||, instead of and.

if [ $sn -ne 3 ] && [ -n "$(printf '%sn' "$start" | sed 's/[0-9]//g')" ]; then

    echo reject

Or you could just use case and a pattern match:

case "$start" in

    [0-9][0-9][0-9]) echo "'$start' is ok";;

    *) echo "'$start' is invalid"; exit 1;;

esac

You don't have any statements in the "true" case of your first if:

if ( [ $# -eq 2 ] )



then

  ##  <-- HERE

elif  ...

Quoting the bash manual:

The syntax of the if command is:

if test-commands; then

  consequent-commands;

[elif more-test-commands; then

  more-consequents;]

[else alternate-consequents;]

fi

Where the important bit is the consequent-commands.