Removing the first space in a line

You may use sed for this:

sed 's/ //' infile >outfile

This applies a substitution to all lines of the file infile that will substitute the first space character with nothing (i.e. remove it). The output is stored in the file outfile. With sed 's/ //N', where N is an integer between 1 and 9, you can pick which space to remove.

If the line is in a shell variable, you could use

var="${var/ /}"

This uses the ${parameter/pattern/string} parameter expansion in bash to do the same thing as the sed command, but on the value in $var. The resulting string is, in this example, then stored back into $var.