GNU Info

(dc.info)Strings

---

Next: Status Inquiry Prev: Parameters Up: Top

---

Enter node , (file) or (file)node

Strings
*******

   DC can operate on strings as well as on numbers.  The only things
you can do with strings are print them and execute them as macros
(which means that the contents of the string are processed as DC
commands).  Both registers and the stack can hold strings, and DC
always knows whether any given object is a string or a number.  Some
commands such as arithmetic operations demand numbers as arguments and
print errors if given strings.  Other commands can accept either a
number or a string; for example, the `p' command can accept either and
prints the object according to its type.

`[CHARACTERS]'
     Makes a string containing CHARACTERS and pushes it on the stack.
     For example, `[foo]P' prints the characters `foo' (with no
     newline).

`a'
     The mnemonic for this is somewhat erroneous: asciify.  The
     top-of-stack is popped.  If it was a number, then the low-order
     byte of this number is converted into a string and pushed onto the
     stack.  Otherwise the top-of-stack was a string, and the first
     character of that string is pushed back.  (This command is a GNU
     extension.)

`x'
     Pops a value off the stack and executes it as a macro.  Normally
     it should be a string; if it is a number, it is simply pushed back
     onto the stack.  For example, `[1p]x' executes the macro `1p',
     which pushes 1 on the stack and prints `1' on a separate line.

     Macros are most often stored in registers; `[1p]sa' stores a macro
     to print `1' into register `a', and `lax' invokes the macro.

`>R'
     Pops two values off the stack and compares them assuming they are
     numbers, executing the contents of register R as a macro if the
     original top-of-stack is greater.  Thus, `1 2>a' will invoke
     register `a''s contents and `2 1>a' will not.

`!>R'
     Similar but invokes the macro if the original top-of-stack is not
     greater (is less than or equal to) what was the second-to-top.

`<R'
     Similar but invokes the macro if the original top-of-stack is less.

`!<R'
     Similar but invokes the macro if the original top-of-stack is not
     less (is greater than or equal to) what was the second-to-top.

`=R'
     Similar but invokes the macro if the two numbers popped are equal.

`!=R'
     Similar but invokes the macro if the two numbers popped are not
     equal.

`?'
     Reads a line from the terminal and executes it.  This command
     allows a macro to request input from the user.

`q'
     During the execution of a macro, this command exits from the macro
     and also from the macro which invoked it.  If called from the top
     level, or from a macro which was called directly from the top
     level, the `q' command will cause DC to exit.

`Q'
     Pops a value off the stack and uses it as a count of levels of
     macro execution to be exited.  Thus, `3Q' exits three levels.