Square bracket ( test condition ) stuff in shell and advance case statement - shell

Question

I have two questions. Lets talk about the simpler one 1st and then we'll talk about the case statement.
consider this simple if else
if fgrep -q '= ' sf
then
echo "blanks in file"
else
echo "no blanks"
fi
[[ `fgrep -q '= ' sf` ]] && echo "blanks there"
# rc=$?
# echo "rc is $rc"
the if condition works like a charm. I am trying to rewrite the same stuff using [[ test condition and it does not exactly work. What is wrong in my test condition.
now the 2nd Question
Actually here is what I am trying to do .
There is this kinda case statement I have
source "/path"
# die is a function that will output standard error and return 1
opta=false
optb=false
while getopts ":abf:" opt; do
case $opt in
a ) $optb && die "Cannot specify option a after specifying option b"
opta=true
;;
b ) $opta && die "Cannot specify option b after specifying option a"
optb=true
;;
f) # Pl see the note below for f
\?) die "Invalid option: -$OPTARG. Abort"
;;
esac
done
shift $(($OPTIND - 1))
test $# -eq 0 && die "You must supply SID"
test $# -eq 1 || die "Too many command-line arguments"
SID=$1
the f is a file option. So 1st two are incompatible if -f is used.
myshell -f /path/file1 -a 500
above is not allowed. I can manage this part so don't worry about it too much
Here is the rock that's stumbling me off path .
-f accepts a file path. The file is an manual override file that has various parameters that will override ones set using the source command . So when It comes to f option it should do the following
check if
file path is valid
2.
if it is valid check if there IS "= "viz. equal to followed by blank- then quit.In other words I dont want blank values || ones that ^blank
3
if both these conditions are met then if the search string s parameter is set in the file then there cannot be any positional parameters passed to the command .
e.g. of manual override file below
p1=v1
p2=v2
s=v3
p3=
# some parameters like p3 need to be set in that case it will take the defaults from the source file if those aren't set
In other words e.g the below command
myshell.ksh -f /path/file1 500
is valid if value of s is NOT set in file1 else it should quit giving an error that positional parameter was supplied when override value was already applied in file -f file1
4
export all the parameters that are set in file1 as overrides to the source file parameters.
e.g. source file has
p1=sv1
and in file1 p1 is set then export p1=v1 from file1
I can manage #4. I just need some insight into $3 for the most. 2,1 and 4 won't harm

Answer 1

Question 1
The [[...]] have no business being there. Use:
fgrep -q '= ' sf && echo "blanks there"
The above runs fgrep on sf. If fgrep indicates success, then the echo command is run.
Question 2
If /path/file1 contains a setting for the s variable and there are positional parameters on the command line, then we are supposed to report an error:
grep '^s=' /path/file1 && [ "$#" -gt 0 ] && echo "ERROR: file has s parameter set and there are positional arguments"
The above checks for two conditions to be true and, if they are both true, it prints an error message. The first condition is:
grep '^s=' /path/file1
The is true if the file /path/file1 has a line that begins with the characters s=. (^ signifies the beginning of a line.) The second condition is:
[ "$#" -gt 0 ]
This return true if the number of positional parameters is greater than zero. If both of those conditions are true, then the echo statement above is executed.
Question 2: Alternate Approach
In this case, we suppose that the variable $filepath has the path and name of the file, such as /path/file1, which contains shell commands for setting variables. The following checks to see if that file is readable. If it is, then it sources all the commands in that file. The next line checks to see if s has been set. If it has and if there are still positional parameters, then it prints a message:
[ -r "$filepath" ] && source "$filepath" # Set all override variables
[ -n "$s" ] && [ "$#" -gt 0 ] && echo "message"
In the test ([...]) statements, note that $filepath and $s are enclosed in double-quotes. This prevents an error should either value be empty. It also prevents errors if the value of filepath contains spaces.
To source a file, it needs not merely to exist but also to be readable. Therefore, the first test above checks for readability (-r) instead of mere existence (-f).
MORE
To check if the source file has any uncommented lines with variables set to empty values:
grep -qE '^[^#]+=$' file1 && echo "message"
In the above ^ matches the beginning of a line.
The regular expression works because [^#] matches any character that is not a hash sign. Since plus sign means one or more of the preceding character, the [^#]+ means a string of one or more characters, none of which are hash signs. Outside of square brackets, a ^ matches the start of a line. So, ^[^#]+ matches any string of non-hash characters starting at the beginning of the line. ^[^#]+= matches if those characters are then followed by an equal sign. Since $ matches the end of a line, then ^[^#]+=$ matches if the line starts with one or more non-hash characters, followed by an equal sign, followed by nothing (the end of the line). Thus, it matches if some variable has its value set to nothing.