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Regarding syntax, this is a simple methodology that I use (by example) to consistently and sanely manage Boolean logic:

# tests
var=
var=''
var=""
var=0
var=1
var="abc"
var=abc

if [[ -n "${var}" ]] ; then
    echo 'true'
fi
if [[ -z "${var}" ]] ; then
    echo 'false'
fi

# results
# var=        # false
# var=''      # false
# var=""      # false
# var=0       # true
# var=1       # true
# var="abc"   # true
# var=abc     # true

If the variable is never declared the answer is: # false

So, a simple way to set a variable to true (using this syntax methodology) would be, var=1; conversely, var=''.

Reference:

-n = True if the length of var string is non-zero.

-z = True if the length of var string is zero.

Regarding syntax, this is a simple methodology that I use (by example) to consistently and sanely manage Boolean logic:

# Tests
var=
var=''
var=""
var=0
var=1
var="abc"
var=abc

if [[ -n "${var}" ]] ; then
    echo 'true'
fi
if [[ -z "${var}" ]] ; then
    echo 'false'
fi

# Results
# var=        # false
# var=''      # false
# var=""      # false
# var=0       # true
# var=1       # true
# var="abc"   # true
# var=abc     # true

If the variable is never declared the answer is: # false

So, a simple way to set a variable to true (using this syntax methodology) would be, var=1; conversely, var=''.

Reference:

-n = True if the length of var string is non-zero.

-z = True if the length of var string is zero.

Regarding syntax, this is a simple methodology that I use (by example) to consistently and sanely manage Boolean logic:

# tests
var=
var=''
var=""
var=0
var=1
var="abc"
var=abc

if [[ -n "${var}" ]] ; then
    echo 'true'
fi
if [[ -z "${var}" ]] ; then
    echo 'false'
fi

# results
# var=        # false
# var=''      # false
# var=""      # false
# var=0       # true
# var=1       # true
# var="abc"   # true
# var=abc     # true

If the variable is never declared the answer is: # false

So, a simple way to set a variable to true (using this syntax methodology) would be, var=1; conversely, var=''.

Reference:

-n = True if the length of var string is non-zero.

-z = True of the length if var string is zero.

Regarding syntax, this is a simple methodology that I use (by example) to consistently and sanely manage Boolean logic:

# tests
var=
var=''
var=""
var=0
var=1
var="abc"
var=abc

if [[ -n "${var}" ]] ; then
    echo 'true'
fi
if [[ -z "${var}" ]] ; then
    echo 'false'
fi

# results
# var=        # false
# var=''      # false
# var=""      # false
# var=0       # true
# var=1       # true
# var="abc"   # true
# var=abc     # true

If the variable is never declared the answer is: # false

So, a simple way to set a variable to true (using this syntax methodology) would be, var=1; conversely, var=''.

Reference:

-n = True if the length of var string is non-zero.

-z = True if the length of var string is zero.

Regarding syntax, this is a simple methodology that I use (by example) to consistently and sanely manage Boolean logic:

# tests
var=
var=''
var=""
var=0
var=1
var="abc"
var=abc

if [[ -n "${var}" ]] ; then
    echo 'true'
fi
if [[ -z "${var}" ]] ; then
    echo 'false'
fi

# results
# var=        # false
# var=''      # false
# var=""      # false
# var=0       # true
# var=1       # true
# var="abc"   # true
# var=abc     # true

If the variable is never declared the answer is: # false

So, a simple way to set a variable to true (using this syntax methodology) would be, var=1; conversely, var=''.

Regarding syntax, this is a simple methodology that I use (by example) to consistently and sanely manage Boolean logic:

# tests
var=
var=''
var=""
var=0
var=1
var="abc"
var=abc

if [[ -n "${var}" ]] ; then
    echo 'true'
fi
if [[ -z "${var}" ]] ; then
    echo 'false'
fi

# results
# var=        # false
# var=''      # false
# var=""      # false
# var=0       # true
# var=1       # true
# var="abc"   # true
# var=abc     # true

If the variable is never declared the answer is: # false

So, a simple way to set a variable to true (using this syntax methodology) would be, var=1; conversely, var=''.

Reference:

-n = True if the length of var string is non-zero.

-z = True of the length if var string is zero.