shtk_bool_check —
    Converts a string to a boolean value
  
    | shtk_bool_check | value [error_message] | 
The shtk_bool_check function takes the
    string value and returns the corresponding boolean
    value according to shell conventions.
shtk_bool_check returns 0 for any
    value representing truth. These include the strings
    ‘yes’ and ‘true’, including any variations in
    their capitalization, and the integer number ‘1’.
shtk_bool_check returns 1 for any
    value representing falsehood. These include the
    strings ‘no’ and ‘false’, including any
    variations in their capitalization, and the integer number
    ‘0’.
local verbose=no
# Parse flags to see if verbose mode is enabled and set verbose=yes.
if shtk_bool_check "${verbose}"; then
    # Print messages.
fi
 
shtk_bool_check prints the error given in
    error_message and exits the shell with non-zero if the
    value does not represent a valid boolean value. If
    error_message is not provided, a default message is
    printed.
shtk_bool_check first appeared in
    shtk 1.4.