diff --git a/doc/src/sgml/ref/pgbench.sgml b/doc/src/sgml/ref/pgbench.sgml
index 41d9030..7b3badf 100644
--- a/doc/src/sgml/ref/pgbench.sgml
+++ b/doc/src/sgml/ref/pgbench.sgml
@@ -971,6 +971,8 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
       integer constants such as <literal>5432</literal>,
       double constants such as <literal>3.14159</literal>,
       references to variables <literal>:</literal><replaceable>variablename</replaceable>,
+      testing whether a variable exists
+      <literal>:{?</literal><replaceable>variablename</replaceable><literal>}</literal>,
       <link linkend="pgbench-builtin-operators">operators</link>
       with their usual SQL precedence and associativity,
       <link linkend="pgbench-builtin-functions">function calls</link>,
diff --git a/src/bin/pgbench/exprparse.y b/src/bin/pgbench/exprparse.y
index 8447e14..2f89142 100644
--- a/src/bin/pgbench/exprparse.y
+++ b/src/bin/pgbench/exprparse.y
@@ -28,6 +28,7 @@ static PgBenchExpr *make_boolean_constant(bool bval);
 static PgBenchExpr *make_integer_constant(int64 ival);
 static PgBenchExpr *make_double_constant(double dval);
 static PgBenchExpr *make_variable(char *varname);
+static PgBenchExpr *make_variable_exists(char *varname);
 static PgBenchExpr *make_op(yyscan_t yyscanner, const char *operator,
 		PgBenchExpr *lexpr, PgBenchExpr *rexpr);
 static PgBenchExpr *make_uop(yyscan_t yyscanner, const char *operator, PgBenchExpr *expr);
@@ -59,9 +60,10 @@ static PgBenchExpr *make_case(yyscan_t yyscanner, PgBenchExprList *when_then_lis
 %type <ival> INTEGER_CONST function
 %type <dval> DOUBLE_CONST
 %type <bval> BOOLEAN_CONST
-%type <str> VARIABLE FUNCTION
+%type <str> VARIABLE VAREXISTS FUNCTION
 
-%token NULL_CONST INTEGER_CONST DOUBLE_CONST BOOLEAN_CONST VARIABLE FUNCTION
+%token NULL_CONST INTEGER_CONST DOUBLE_CONST BOOLEAN_CONST
+%token VARIABLE VAREXISTS FUNCTION
 %token AND_OP OR_OP NOT_OP NE_OP LE_OP GE_OP LS_OP RS_OP IS_OP
 %token CASE_KW WHEN_KW THEN_KW ELSE_KW END_KW
 
@@ -140,6 +142,7 @@ expr: '(' expr ')'			{ $$ = $2; }
 	| DOUBLE_CONST			{ $$ = make_double_constant($1); }
 	/* misc */
 	| VARIABLE				{ $$ = make_variable($1); }
+	| VAREXISTS				{ $$ = make_variable_exists($1); }
 	| function '(' elist ')' { $$ = make_func(yyscanner, $1, $3); }
 	| case_control			{ $$ = $1; }
 	;
@@ -213,6 +216,16 @@ make_variable(char *varname)
 
 /* binary operators */
 static PgBenchExpr *
+make_variable_exists(char *varname)
+{
+	PgBenchExpr *expr = pg_malloc(sizeof(PgBenchExpr));
+
+	expr->etype = ENODE_VAREXISTS;
+	expr->u.variable.varname = varname;
+	return expr;
+}
+
+static PgBenchExpr *
 make_op(yyscan_t yyscanner, const char *operator,
 		PgBenchExpr *lexpr, PgBenchExpr *rexpr)
 {
diff --git a/src/bin/pgbench/exprscan.l b/src/bin/pgbench/exprscan.l
index 5c1bd88..ff2b586 100644
--- a/src/bin/pgbench/exprscan.l
+++ b/src/bin/pgbench/exprscan.l
@@ -191,6 +191,13 @@ notnull			[Nn][Oo][Tt][Nn][Uu][Ll][Ll]
 					yylval->bval = false;
 					return BOOLEAN_CONST;
 				}
+:\{\?{alnum}+\}	{
+					/* no pg_strndup? */
+					yylval->str = pg_strdup(yytext + 3);
+					/* scratch final '}' */
+					yylval->str[strlen(yylval->str)-1] = '\0';
+					return VAREXISTS;
+				}
 {digit}+		{
 					yylval->ival = strtoint64(yytext);
 					return INTEGER_CONST;
diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c
index 8529e7d..3ddceffe 100644
--- a/src/bin/pgbench/pgbench.c
+++ b/src/bin/pgbench/pgbench.c
@@ -2360,6 +2360,10 @@ evaluateExpr(TState *thread, CState *st, PgBenchExpr *expr, PgBenchValue *retval
 				return true;
 			}
 
+		case ENODE_VAREXISTS:
+				setBoolValue(retval, lookupVariable(st, expr->u.variable.varname) != NULL);
+				return true;
+
 		case ENODE_FUNCTION:
 			return evalFunc(thread, st,
 							expr->u.function.function,
diff --git a/src/bin/pgbench/pgbench.h b/src/bin/pgbench/pgbench.h
index 6983865..284443e 100644
--- a/src/bin/pgbench/pgbench.h
+++ b/src/bin/pgbench/pgbench.h
@@ -58,6 +58,7 @@ typedef enum PgBenchExprType
 {
 	ENODE_CONSTANT,
 	ENODE_VARIABLE,
+	ENODE_VAREXISTS,
 	ENODE_FUNCTION
 } PgBenchExprType;
 
diff --git a/src/bin/pgbench/t/001_pgbench_with_server.pl b/src/bin/pgbench/t/001_pgbench_with_server.pl
index 0929418..f6c2f53 100644
--- a/src/bin/pgbench/t/001_pgbench_with_server.pl
+++ b/src/bin/pgbench/t/001_pgbench_with_server.pl
@@ -283,6 +283,8 @@ pgbench(
 		qr{command=96.: int 1\b},    # :scale
 		qr{command=97.: int 0\b},    # :client_id
 		qr{command=98.: int 5432\b}, # :random_seed
+		qr{command=99.: boolean false\b}, # var exists
+		qr{command=100.: boolean true\b},
 	],
 	'pgbench expressions',
 	{   '001_pgbench_expressions' => q{-- integer functions
@@ -407,6 +409,9 @@ SELECT :v0, :v1, :v2, :v3;
 \set sc debug(:scale)
 \set ci debug(:client_id)
 \set rs debug(:random_seed)
+-- test variable existence
+\set no debug(:{?no_such_variable})
+\set yes debug(:{?cs})
 } });
 
 # random determinism when seeded