Otherware/Otherware_1_SB_Development.iso/amiga/utility/cli/sksh017.lzh/doc/Diffs.doc

Text File | 1991-05-04 | 5.0 KB | 265 lines

                         SKsh/ksh Differences

                                 SKsh

                    A ksh-like Shell for the Amiga

                              Version 1.7


                         (Copyright) 1988-1991

                              Steve Koren

                              May 4, 1991











































       Introduction

     This  document  describes some of the  differences between SKsh
     and ksh  under Unix.  It does not even begin to cover them all.
     If you need  to  have  specific information, compare the appro-
     priate sections of the two manuals.

     In  general, scripts may be written which run under either SKsh
     or ksh by testing the $SHELL parameter:

        if [ "$SHELL" = 'sksh' ]
        then
          echo 'do some SKsh/AmigaDos specific things here'
        elif [ "$SHELL" = '/bin/ksh' ]
        then
          echo 'do some ksh/UNIX specific things here'
        fi


       Differences List

     Alias and Function Resolution

        SKsh  resolves alias and  function names when they are logi-
        cally encountered.   ksh  resolves them when they are physi-
        cally encountered.  This  leads  to  different behaviours in
        functions.  For  example, in SKsh, you can define a function
        that uses an alias that  you  define after the function.  As
        long  as  the  alias  is  defined before the function is ex-
        ecuted  (but  not  necessarily  before it is  defined), SKsh
        will  execute the alias normally.   In  ksh,  on  the  other
        hand, the alias  must  be  defined as such when the function
        is defined, not when it is executed.


     Assignment Syntax

        SKsh  permits  spaces  to  surround the '=' in an assignment
        statement.  ksh does not.


     ${var:val} Operations

        SKsh supports only a subset of these operations.












       SKSH Amiga Shell             Page 2         SKsh/ksh Differences









     vi mode

        ksh  has  a  command line editing mode that is similar to vi
        bindings.   SKsh   provides  user  definable editing and two
        functions  which  define editing styles similar to emacs and
        vi.  A few of  the  commands, such as the ^r history search,
        work slightly differently than they do in the Un*x ksh.


     In-line parameter assignment

        ksh  permits variables to be assigned to while being used as
        a parameter.  For example,

          export COLUMNS=80

        SKsh does not  permit this.  You must perform the assignment
        and export separately.


     Job Control

        ksh has job control.  SKsh does not.


     Path Separator Character

        ksh uses ':' as a  path  separator character.  Since the co-
        lon is a  legal character in AmigaDos path names, a comma is
        used instead.


     Function Definition Syntax

        The  SKsh  function  definition  syntax using the 'function'
        keyword is  compatible with ksh, but ksh also permits an al-
        ternate syntax using 'function() { }' that SKsh does not.


     Set vs. Options

        ksh  uses  the  'set'  keyword to  set  options to the shell
        itself.  SKsh  uses  'set'  to  list  alias,  variables, and
        functions.   SKsh  uses  the   'option' command to set shell
        options.   These   options are, with only a few  exceptions,
        different from their ksh counterparts.










       SKSH Amiga Shell             Page 3         SKsh/ksh Differences









     Scoping Rules

        The SKsh scoping rules are  different than the scoping rules
        in  in  ksh.   Ksh  supports the 'typeset' keyword to create
        local  variables; SKsh controls this with an option flag and
        the  'local' command.  In addition, SKsh local variables can
        be turned off entirely to emulate the sh scoping rules.


     Builtin Commands

        SKsh  accomplishes many  things  with  builtin commands that
        ksh  accomplishes with external binaries.  In addition, Unix
        has  many  more  of  these  commands than the Amiga and SKsh
        combined do or ever will.   If  its  on  Unix,  and  not  on
        AmigaDos, you'll probably have to write it if you want it.

        In  addition, many of the SKsh commands accept different pa-
        rameters than  their  Unix  counterparts with the same name.
        Some of them  also  act  differently; for example, 'read' in
        Unix  reads  a  single  parameter  separated by  IFS,  while
        'read' in SKsh reads a whole line.


     until...do...done statement

        SKsh does  not  support this construct.   I was not in a big
        hurry  to  add  it,  since  it  is  simply a while..do..done
        statement with the test automatically inverted.


     Parameter Breaks

        SKsh  breaks  parameters in  different places than ksh.  For
        example,  'foo'$foo  is  one  parameter in ksh, but  two  in
        SKsh.  To make it one in SKsh, use double quotes around  the
        whole expression: "foo$foo", or use $(concat "foo" "$foo").


     Standard Error Redirection

        Under AmigaDos,  there  is  no  distinction between standard
        output  and  standard error.  Thus, you cannot redirect them
        independently in SKsh.