A simple standard library for posix sh, WIP

stdlib.sh

#!/bin/sh
## sh stdlib


plus_equals() { FUNCTION="plus_equals()";
    
    ## Handle options
    case "$1" in
        -h)
            echo;
            echo "$FUNCTION: add an amount to the variable";
            echo;
            echo '  usage: plus_equals -h';
            echo '  usage: plus_equals [--] variable amount';
            echo;
            return 1;
            ;;
        
        --) shift; ;;
        -*) throw "$FUNCTION: Invalid option: $1"; return 1; ;;
    esac;
    
    ## Get the arguments
    VARIABLE="$1";
    AMOUNT="$2";
    
    ## Check if the variable is empty
    if [ -z "$VARIABLE" ]; then
        throw "$FUNCTION: Empty variable name.";
        return 1;
    fi;
    
    ## Check if the amount is empty
    if [ -z "$AMOUNT" ]; then
        throw "$FUNCTION: Empty amount.";
        return 1;
    fi;
    
    ## Check if the variable is undefined
    if ! is_defined "$VARIABLE"; then
        throw "$FUNCTION: Undefined variable: $VARIABLE";
        return 1;
    fi;
    
    ## Add the amount to the variable
    eval "$VARIABLE=\$((\$$VARIABLE + \$AMOUNT));"
};


increment() { FUNCTION="increment()";
    
    ## Handle options
    case "$1" in
        -h)
            echo;
            echo "$FUNCTION: increment a variable by one";
            echo;
            echo '  usage: increment -h';
            echo '  usage: increment [--] variable';
            echo;
            return 1;
            ;;
        
        --) shift; ;;
        -*) throw "$FUNCTION: Invalid option: $1"; return 1; ;;
    esac;
    
    ## Get the arguments
    VARIABLE="$1";
    
    ## Add one to the variable, let plus_equals() error handle
    plus_equals "$VARIABLE" 1;
    
};

decrement() { FUNCTION="decrement()";
    
    ## Handle options
    case "$1" in
        -h)
            echo;
            echo "$FUNCTION: decrement a variable by one";
            echo;
            echo '  usage: decrement -h';
            echo '  usage: decrement [--] variable';
            echo;
            return 1;
            ;;
        
        --) shift; ;;
        -*) throw "$FUNCTION: Invalid option: $1"; return 1; ;;
    esac;
    
    ## Get the arguments
    VARIABLE="$1";
    
    ## Subtract one from the variable, let plus_equals() error handle
    plus_equals "$VARIABLE" -1;
    
};

is_defined() { FUNCTION="is_defined()";
    
    ## Handle options
    case "$1" in
        -h)
            echo;
            echo "$FUNCTION: check if a variable is defined";
            echo;
            echo '  usage: is_defined -h';
            echo '  usage: is_defined [--] variable';
            echo;
            return 1;
            ;;
        
        --) shift; ;;
        -*) throw "$FUNCTION: Invalid option: $1"; return 1; ;;
    esac;
    
    ## Get the arguments
    VARIABLE="$1";
    
    ## Check if the variable is empty
    if [ -z "$VARIABLE" ]; then
        throw "$FUNCTION: Empty variable name.";
        return 1;
    fi;
    
    ## Check if the variable is defined
    [ -n "$(eval echo "\$$VARIABLE")" ];
};

std_HARDFAIL=true;
throw() { FUNCTION="throw()";
    
    ## Internal variables
    FORCEFAIL=false;
    FORCELIVE=false;
    
    ## Handle options
    ## Ignore shellcheck warnings about single-quote expansions
    # shellcheck disable=SC2016
    case "$1" in
        -h)
            echo;
            echo "$FUNCTION: Throw an error";
            echo;
            echo '  if $std_HARDFAIL is true, the script will exit';
            echo '  if the first argument is -f, the script will exit (regardless of $std_HARDFAIL)';
            echo '  if the first argument is -l, the script will NOT exit (regardless of $std_HARDFAIL)';
            echo;
            echo '  usage: throw -h';
            echo '  usage: throw [-f] [error ...]';
            echo '  usage: throw [-l] [error ...]';
            echo;
            return 1; ;;
        
        -f)
            FORCELIVE=false;
            FORCEFAIL=true;
            shift; ;;
        
        -l)
            FORCEFAIL=false;
            FORCELIVE=true;
            shift; ;;
        
        --) shift; ;;
        -*) throw "$FUNCTION: Invalid option: $1"; return 1; ;;
    esac;
    
    ## Get the arguments
    ERROR="$*";
    
    ## Write the error to stderr
    echo "$ERROR" >&2;
    
    ## Exit the function if HARDFAIL or FORCEFAIL are set, but not if FORCELIVE is set.
    if $std_HARDFAIL || $FORCEFAIL && ! $FORCELIVE; then
        exit 1;
    fi;
};