BS(1,C) AIX Commands Reference BS(1,C) ------------------------------------------------------------------------------- bs PURPOSE Compiles and interprets modest-size programs. SYNTAX +-----------------------+ bs ---| +------------+ |---| +- file -| |-+ +--- flag ---+ ^ | +--------+ Note: This command does not have MBCS support. DESCRIPTION This compiler/interpreter provides interactive program development and debugging. To simplify program testing, it minimizes formal data declaration and file manipulation, allows line-at-a-time debugging, and provides trace and dump facilities and run-time error messages. The optional command line parameter file specifies a file of program statements that the compiler reads before it reads from the standard input. By default, statements read from this file are compiled for later execution. Likewise, statements entered from the standard input are normally executed immediately (see the compile keyword on page 2 and the execute keyword on page 2). Unless the final operation is assignment, the result of an immediate expression statement is displayed. Additional command line flags can be passed to the program using the built-in functions arg and narg (explained in more detail on page 7). Program lines must conform to one of the following formats: statement label statement The bs interpreter accepts labeled statements only when it is compiling statements. A label is a name immediately followed by a colon. A label and a variable can have the same name. If the last character of a line is a \ (backslash), the statement continues on the following physical line. A statement consists of either an expression or a keyword followed by zero or more expressions. Processed July 12, 1991 BS(1,C) 1 BS(1,C) AIX Commands Reference BS(1,C) Statement Syntax break Exits the innermost for or while loop. clear Clears the symbol table and removes compiled statements from memory. A clear statement is always executed immediately. compile [expr] Causes succeeding statements to be compiled (overrides the immediate execution default). The optional expression is evaluated and used as a file name for further input. In this latter case, the symbol table and memory are cleared first. A compile statement is always executed immediately. continue Transfers control to the loop-continuation test of the current for or while loop. dump [name] Displays the name and current value of every global variable or, optionally, of the named variable. After an error or interrupt, a dump statement displays the number of the last statement and (possibly) the user-function trace. exit [expr] Returns to the system level. The expression is returned as process status. execute Changes to immediate execution mode (pressing the INTERRUPT [Ctrl-C] key has the same effect). This statement does not cause stored statements to execute (see run on page 4). for name=expr expr statement for name=expr expr statement... next for expr, expr, expr statement for expr, expr, expr statement... Processed July 12, 1991 BS(1,C) 2 BS(1,C) AIX Commands Reference BS(1,C) next Repetitively performs, under the control of a named variable, a statement (first format) or a group of statements (second format). The variable takes on the value of the first expression, and is then increased by one on each loop until its value exceeds the value of the second expression. The third and fourth formats require three expressions separated by commas. The first of these is the initialization, the second is the test (true to continue), and the third is the loop-continuation action. fun f ([a,...]) [v,...] statement... nuf Defines the function name (f), parameters (a), and local variables (v) for a user-written function. Up to 10 parameters and local variables are allowed. Such names cannot be arrays, nor can they be I/O associated. Function definitions can not be nested. freturn Signals the failure of a user-written function. Without interrogation, the freturn statement returns zero. (See the unary interrogation operator ? discussed on page 6.) With interrogation, the freturn statement transfers to the interrogated expression, possibly bypassing intermediate function returns. goto name Passes control to the compiled statement with the matching label. ibase n Sets the input base to n. The only supported values for n are 8, 10 (the default), and 16. Hexadecimal values 10-15 are printed as alphabetic characters a-f. An ibase statement is always executed immediately. if expr statement if expr statement... [else statement...] fi Performs a statement (first format) or group of statements (second format) if the expression evaluates to nonzero. The strings 0 and "" (null) evaluate as zero. In the second format, Processed July 12, 1991 BS(1,C) 3 BS(1,C) AIX Commands Reference BS(1,C) an optional else statement allows a group of statements to be performed when the first group is not. The only statement permitted on the same line with an else statement is an if statement; only other fi statements can be on the same line with an fi statement. You can combine an else and an if statement into an elif statement. Only a single fi statement is required to close an if...elif...[else...] sequence. include expr The expression must evaluate to the name of a file containing program statements. Such statements become part of the program being compiled. An include statement may not be nested, and is always executed immediately. obase n Sets the output base to n. The only supported values for n are 8, 10 (the default), and 16. Hexadecimal values 10-15 are entered as alphabetic characters a-f. A leading digit is required when a hexadecimal number begins with an alphabetic character (that is, "f0a" must be entered as "0f0a"). Like an ibase statement, an obase statement is always executed immediately. onintr label onintr Provides program control of interrupts. In the first format, control passes to the label given, just as if a goto had been performed when the onintr statement was executed. The effect of the onintr statement is cleared after each interrupt. In the second format, pressing the INTERRUPT (Ctrl-C) key ends the bs command. return [expr] Evaluates the expression and passes the result back as the value of a function call. If you do not provide an expression, the function returns zero. run Passes control to the first compiled statement. The random number generator is reset. If a file contains a run statement, it should be the last statement; a run statement is always executed immediately. stop Stops execution of compiled statements and returns to immediate mode. trace [expr] Controls function tracing. If you do not provide an expression or if it evaluates to zero, tracing is turned off. Otherwise, a record of user-function calls/returns is written. Each return decreases by one the trace statement expression value. while expr statement while expr Processed July 12, 1991 BS(1,C) 4 BS(1,C) AIX Commands Reference BS(1,C) statement... next A while statement is similar to a for statement except that only the conditional expression for loop continuation is given. ! AIXcmd Runs an AIX command, then returns control to the bs command. #comment Inserts a comment line. Expression Syntax name Specifies a variable or, when followed immediately by a colon, a label. Names are composed of a letter (uppercase or lowercase) optionally followed by letters and digits. Only the first six characters of a name are significant. Except for names declared locally in fun statements, all names are global. Names can take on numeric (double float) values or string values or be associated with input/output (see the built-in function open on page 10). name([expr[, expr]...) Calls function name and passes to it the parameters in parentheses. Except for built-in functions (listed in the following text), name must be defined in a fun statement. Function parameters are passed by value. name[expr[, expr]...] References either arrays or tables (see built-in function table on page 10). For arrays, each expression is truncated to an integer and used as a specifier for the name. The resulting array reference is syntactically identical to a name; "a[1,2]" is the same as "a[1][2]". The truncated expressions must be values between 0 and 32767. number Represents a constant numerical value. This number can be expressed in integer, decimal, or scientific notation (it can contain digits, an optional decimal point, and an optional e followed by a possibly signed exponent). string Character string delimited by " " (double quotation marks). The \ (backslash) is an escape character that allows the double quotation mark (\"), new-line character (\n), carriage return (\r), backspace (\b), and tab (\t) characters to appear in a string. When not immediately followed by these special characters, \ stands for itself. (expr) Parentheses alter the normal order of evaluation. Processed July 12, 1991 BS(1,C) 5 BS(1,C) AIX Commands Reference BS(1,C) (expr, expr[, expr]...) [expr] The bracketed expression outside the parentheses functions as a subscript to the list of expressions within the parentheses. List elements are numbered from the left, starting at zero. The expression: (False, True) [ a == b ] has the value True if the comparison is true. expr op expr Except for the assignment, concatenation, and relational operators, both operands are converted to numeric form before the operator is applied. Unary Operators ?expr The interrogation operator ("?") tests for the success of the expression rather than its value. It is useful for testing end of file, for testing the result of the eval built-in function, and for checking the return from user-written functions (see freturn on page 3). An interrogation trap ( end of file, for example), causes an immediate transfer to the most recent interrogation, possibly skipping assignment statements or intervening function levels. -expr Negates the expression. ++name Increases by one the value of the variable (or array reference). --name Decreases by one the value of the variable. !expr The logical negation of the expression. Binary Operators (in increasing precedence) = The assignment operator. The left operand must be a name or an array element. It acquires the value of the right operand. The assignment operator binds right to left; all other operators bind left to right. _ The concatenation operator (the underline character). & | Logical AND operator and logical OR operator. The result of the following: expr & expr is 1 (true) only if both of its parameters are nonzero (true); the result is 0 (false) if one or both of its parameters are 0 (false). Processed July 12, 1991 BS(1,C) 6 BS(1,C) AIX Commands Reference BS(1,C) The result of this: expr | expr is 1 (true) if one or both of its expressions are nonzero (true); the result is 0 (false) only if both of its expressions are 0 (false). Both operators treat a null string as a zero. < <= > >= == != The relational operators (< less than; <= less than or equal to; > greater than; >= greater than or equal to; == equal to, != not equal to) return 1 if the specified relation is true. They return 0 (false) otherwise. Relational operators at the same level extend as follows: a>b>c is the same as a>b & b>c. A string comparison is made if both operands are strings. The comparison is based on the collating sequence specified in the environment variables LANG and LC_COLLATE. + - Addition and subtraction operators. * / % Multiplication, division, and remainder operators. ^ Exponentiation operator. Functions Dealing With Arguments arg(i) Returns the value of the i-th actual argument at the current function call level. At level zero, arg returns the i-th command-line argument. For example, arg(0) returns "bs". narg( ) Returns the number of arguments passed. At level zero, it returns the command line argument count. Mathematical Functions abs(x) Returns the absolute value of x. atan(x) Returns the arctangent of x. ceil(x) Returns the smallest integer not less than x. cos(x) Returns the cosine of x. exp(x) Returns e raised to the power x. floor(x) Returns the largest integer not greater than x. log(x) Returns the natural logarithm of x. Processed July 12, 1991 BS(1,C) 7 BS(1,C) AIX Commands Reference BS(1,C) rand( ) Returns a uniformly distributed random number between zero and one. sin(x) Returns the sine of x. sqrt(x) Returns the square root of x. String Functions size(s) Returns the size (length in bytes) of s. format(f, a) Returns the formatted value of a, f being a format specification string in the style of the printf subroutine. Use only the %...f, %...e, and %...s formats. index(x, y) Returns a number that is the first position in x containing a character that any of the characters in y matches. If there is no match, the index function yields zero. For two-byte extended characters, the index function returns the location of the first byte. trans(s, f, t) Translates characters in the source string s which match characters in f with characters having the same position in t. Source characters that do not appear in f are copied unchanged into the translated string. If string f is longer than t, source characters that match characters found in the excess portion of f do not appear in the translated string. subst(s, start, length) Returns the substring of s defined by starting position and length. match(string, pattern) mstring(n) This function returns the number of characters in string that match pattern. The characters ., "*", "?" [, ], ^ (when inside square brackets), \( and \) have the following special meanings (see "ed, red" for a more detailed discussion of this special notation): . Matches any character except the new-line character. * Matches zero or more occurrences of the pattern element that it follows (for example, ".*" matches zero or more occurrences of any character except the new-line character). $ Specifies the end of the line. Processed July 12, 1991 BS(1,C) 8 BS(1,C) AIX Commands Reference BS(1,C) [.-.] [...] Matches any one character in the specified range ([.-.]) or list ([...]), including the first and last characters. [^.-.] [^...] Matches any character except the new-line character and the remaining characters in the range or list. A circumflex (^) has this special meaning only when it immediately follows the left bracket. [].-.] []...] Matches ] or any character in the list. The right square bracket does not terminate such a list when it is the first character within the list (after an initial ^, if any). \(...\) Marks a substring and matches it exactly. To succeed, a pattern must match from the beginning of the string. It also matches the longest possible string. Consider, for example: match('a123ab123',".*\([a-z]\)") == 6 In this instance, ".*" matches "a123a" (the longest string that precedes a character in the range a-z); "\([a-z]\)" matches "b", giving a total of six characters matched in the string. In an expression such as [a-z], the minus means "through" according to the current collating sequence. A collating sequence may define equivalence classes for use in character ranges. See "Introduction to International Character Support" in Managing the AIX Operating System for more information on collating sequences and equivalence classes. Note: If you have selected a specific locale (using either the LANG or LC_COLLATE environment variable), it may not be possible to specify an equivalence class of characters using a range expression. In such cases, use a character class expression rather than a standard range expression. For information about character class expressions, see the note on page ed-3 under the ed, red command. Processed July 12, 1991 BS(1,C) 9 BS(1,C) AIX Commands Reference BS(1,C) The mstring function returns the nth substring in the last call to match (n must be between 1 and 10 inclusive). File-Handling Functions open(name, file, mode) close(name) The name parameter must be a legal variable name (passed as a string). For the open function, the file parameter may be: o A 0, 1, or 2 for standard input, output, or error output, respectively o A string representing a file name o A string beginning with an !, representing a command to be run (via the sh -c) command. The mode flag must be either r (read), w (write), W (write without new-line character), or a (append). After a close function, the name becomes an ordinary variable. The initial associations are: open("get", 0, "r") open("put", 1, "w") open("puterr", 2, "w") access(p, m) Performs the access system call. Parameter p is the path name of a file; m is a bit pattern representing the requested mode of access. This function returns a 0 if the request is permitted and -1 if it is denied. (See AIX Operating System Technical Reference for an extensive discussion of this system call.) ftype(s) Returns a single character indicating file type: f for regular file, p for FIFO (named pipe), d for directory, b for block special, or c for character special. Table Functions table(name, size) A table in the bs compiler is an associatively accessed, one-dimensional array. Subscripts (called keys) are strings (numbers are converted). The name parameter must be a bs variable name (passed as a string). The size parameter sets the minimum number of elements to be allocated. On table overflow, the bs compiler writes an error message. item(name, i) Processed July 12, 1991 BS(1,C) 10 BS(1,C) AIX Commands Reference BS(1,C) key( ) The item function accesses table elements sequentially (in normal use, there is an orderly progression of key values). Where the item function accesses values, the key function accesses the subscript of the previous item call. The name parameter should not be quoted. Since exact table sizes are not defined, the interrogation operator should be used to detect end-of-table; for example: table("t",100) . . . #If word contains "party", the following expression #adds one to the count of that word: ++t[word] . . . # To display the key/value pairs: for i=0, ?(s=item(t, i)), ++i if key() put=key()_":"_s iskey(name, word) Tests whether the key word exists in the table name and returns 1 for true or 0 for false. Miscellaneous Functions eval(string) The string parameter is evaluated as an expression. The function is handy for converting numeric strings to numbers. The eval function can also be used as a crude form of indirection, as in: name = "xyz" eval("++"_name) which increments the variable "xyz". In addition, eval preceded by the interrogation operator permits you to control bs compiler error conditions. For example: ?eval("open(\"X\",\"XXX\", \"r\")") returns the value 0 if there is no file named "XXX" (instead of halting your program). The following performs a goto to the label "L:" (if it exists): label="L:" if!(?eval("goto"_label))puterr="no label" Processed July 12, 1991 BS(1,C) 11 BS(1,C) AIX Commands Reference BS(1,C) plot(request, args) The plot function produces output on devices recognized by the tplot command. Some requests do not apply to all plotters. All requests except 0 and 12 are implemented by piping characters to the tplot command. The requests are as follows: Requests Function plot(0, term) Causes further plot output to be piped into the tplot command with a flag of -Tterm. plot(1) "Erases" the plotter. plot (2, string) Labels the current point with string. plot(3, x1, y1, x2, y2) Draws a line between (x1, y1) and (x2, y2). plot(4, x, y, r) Draws a circle with center (x, y) and radius r. plot(5, x1, y1, x2, y2, x3, y3) Draws an arc (counterclockwise) with center (x1, y1) and endpoints (x2, y2) and (x3, y3). plot(6) Not implemented. plot(7, x, y) Makes the current point at (x, y). plot(8, x, y) Draws a line from the current point to (x, y). plot(9, x, y) Draws a point at (x, y). plot(10, string) Sets the line mode to string. plot(11, x1, y1, x2, y2) Makes (x1, y1) the lower left corner of the plotting area and (x2, y2) the upper right corner of the plotting area. Processed July 12, 1991 BS(1,C) 12 BS(1,C) AIX Commands Reference BS(1,C) Requests Function plot(12, x1, y1, x2, y2) Causes subsequent x (y) coordinates to be multiplied by x1 (y1) and then added to x2 (y2) before they are plotted. The initial scaling is plot(12, 1.0, 1.0, 0.0, 0.0). last() In immediate mode, the last function returns the most recently computed value. RELATED INFORMATION See the following commands: "ed, red" and "sh, Rsh." See the access system call, the printf subroutine, and the plot file in AIX Operating System Technical Reference. Processed July 12, 1991 BS(1,C) 13