Functional Programming with Bash

CraigR8806 0
Viewed 39

How would I implement something similar to functional programming within bash?

I have a function:

requestPassword(){
    
    passwordValidated=false

    while [ "$passwordValidated" = "false" ];do
         tput clear
         [ -n "$infomsg" ] && echo -e "$infomsg" >&2
         [ -n "$errmsg" ] && echo -e "$errmsg" >&2
         read -s -p "some prompt:" pass >&2
         errmsg=$()#do some validation
         [ -n "$errmsg" ] && continue
         passwordValidated=true
    done
    echo "$pass"
}

But I want to make it as generic as possible to work with different systems

Maybe I want to ask the password for an encrypted file Maybe I want to ask the password for a system user Maybe I want to use this function to request a new password from a user

The idea would be that I could pass this function a function that takes in a pass parameter and only outputs something if validation failed

bash functional-programming
2 Answers

You can pass a function name as an argument

requestPassword(){
    local infomsg="$1"
    local validator=${2:-the_default_validator_function}
    # ...
    local errmsg
    errmsg=$( "$validator" "$pass" )
    # ...
}

then

# a valid "foobar" password contains the substring "foo"
foobarPasswordValidator() { [[ $1 == *foo* ]]; }

pass=$(requestPassword "Enter your FooBar password" foobarPasswordValidator)

If you don't have a default validator, use : or true -- they accept arguments, ignore them(1) and return a "success" exit status.

(1) ignored after any parameter expansions have occurred

glenn jackman0

This is my solution. Please feel free to add any more insight you may have on this topic

requestPassword(){
    infomsg="$1"
    passwordValidated=false

    while [ "$passwordValidated" = "false" ];do
        tput clear
        [ -n "$infomsg" ] && echo -e "$infomsg" >&2
        [ -n "$errmsg" ] && echo -e "$errmsg" >&2
        read -s -p "some prompt:" pass >&2
        errmsg=$(dynPasswordValidation "$pass")
        [ -n "$errmsg" ] && continue
        passwordValidated=true
   done
   echo "$pass"
}

You would then have other functions that would call this function for specific password requests but would define dynPasswordValidation function prior to the call like so:

requestCurrentEncryptedFilePassword(){
    infomsg="Requesting password for encrypted file"
    
    dynPasswordValidation(){
        [ -n "$(openssl $encalg -d -in $encfile -pass "pass:$1" 2>&1>/dev/null)" ] && echo "Looks like that password didn't work" && return
    }
    pass="$(requestPassword "$infomsg")"
}


requestNewEncryptedFilePassword(){
    infomsg="Requesting new password for encrypted file"
    dynPasswordValidation(){
        pass="$1"
        echo >&2
        read -p -s "veri prompt" pass_veri >&2
        echo >&2
        [ "$pass" != "$pass_veri" ] && echo "Looks like the passwords didn't match" && return
        [ -n "$(#run the password through a set of password rules)" ] && echo "Looks like the password is not up to snuff..." && return
    }
    pass="$(requestPassword "$infomsg")"
}
CraigR88060
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