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Full Discussion: Help with retaining variable scope
Top Forums Shell Programming and Scripting Help with retaining variable scope Post 302555938 by radoulov on Friday 16th of September 2011 06:58:25 AM
Old 09-16-2011
Quote:
Originally Posted by bakunin
I respectfully disagree with radoulov. The reason, why your value is not retained is because it is incremented in a subshell.
Hi bakunin,
if I'm not missing something, in the OP's example the value of the variable is not incremented in a subshell
(unless executed by the Bourne shell, because it seems that sh uses a subshell for redirected loops):

Code:
while read ...
Value=`expr $Value + $Count`
...
echo "Value=$Value"

Something like:

Code:
$ unset v
$ while read ; do v=$REPLY; done<<<1
$ echo $v
1

The OP is verifying the value of the variable inside the script, not outside of it.

Your cat ... | while read ... example demonstrates another KornShell feature: the last builtin command in a pipeline being executed in the parent shell.

Consider the following examples:

Code:
$ echo ok > infile
$ sh -c 'cat infile | while read v; do myvar=$v;done; echo $myvar'

$ bash -c 'cat infile | while read v; do myvar=$v;done; echo $myvar'

$ ksh -c 'cat infile | while read v; do myvar=$v;done; echo $myvar'
ok

This is because of the previously mentioned KornShell feature.

And this is the OP's case:

Code:
$ echo ok > infile
$ sh -c 'while read v; do myvar=$v;done<infile; echo $myvar'

$ ksh -c 'while read v; do myvar=$v;done<infile; echo $myvar'
ok
$ bash -c 'while read v; do myvar=$v;done<infile; echo $myvar'
ok

In this case the old Bourne shell behaves differently.

Regards
radoulov

P.S. Actually this aspect of some implementations of the Bourne shell is covered in the FAQ.
Last edited by radoulov; 09-16-2011 at 09:33 AM.. Reason: Clarification.
 

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LEARN ABOUT DEBIAN

sdl::gfx::imagefilter

pods::SDL::GFX::ImageFilter(3pm)			User Contributed Perl Documentation			  pods::SDL::GFX::ImageFilter(3pm)

NAME

       SDL::GFX::ImageFilter - image filtering functions

CATEGORY

       TODO, GFX

METHODS

   MMX_detect
       int gfx_image_MMX_detect()      CODE:	       SDL_imageFilterMMXdetect();

   MMX_off
       void gfx_image_MMX_off()      CODE:	     SDL_imageFilterMMXoff();

   MMX_on
       void gfx_image_MMX_on()	    CODE:	    SDL_imageFilterMMXon();

   add
       int gfx_image_add(Src1, Src2, Dest, length)	unsigned char *Src1	 unsigned char *Src2	  unsigned char *Dest	   int length
	    CODE:	    RETVAL = SDL_imageFilterAdd(Src1, Src2, Dest, length);	OUTPUT: 	  RETVAL

   mean
       int gfx_image_mean(Src1, Src2, Dest, length)	 unsigned char *Src1	  unsigned char *Src2	   unsigned char *Dest	    int length
	    CODE:	    RETVAL = SDL_imageFilterMean(Src1, Src2, Dest, length);	 OUTPUT:	   RETVAL

   sub
       int gfx_image_sub(Src1, Src2, Dest, length)	unsigned char *Src1	 unsigned char *Src2	  unsigned char *Dest	   int length
	    CODE:	    RETVAL = SDL_imageFilterSub(Src1, Src2, Dest, length);	OUTPUT: 	  RETVAL

   abs_diff
       int gfx_image_abs_diff(Src1, Src2, Dest, length)      unsigned char *Src1      unsigned char *Src2      unsigned char *Dest	int length
	    CODE:	    RETVAL = SDL_imageFilterAbsDiff(Src1, Src2, Dest, length);	    OUTPUT:	      RETVAL

   mult
       int gfx_image_mult(Src1, Src2, Dest, length)	 unsigned char *Src1	  unsigned char *Src2	   unsigned char *Dest	    int length
	    CODE:	    RETVAL = SDL_imageFilterMult(Src1, Src2, Dest, length);	 OUTPUT:	   RETVAL

   mult_nor
       int gfx_image_mult_nor(Src1, Src2, Dest, length)      unsigned char *Src1      unsigned char *Src2      unsigned char *Dest	int length
	    CODE:	    RETVAL = SDL_imageFilterMultNor(Src1, Src2, Dest, length);	    OUTPUT:	      RETVAL

   mult_div_by_2
       int gfx_image_mult_div_by_2(Src1, Src2, Dest, length)	  unsigned char *Src1	   unsigned char *Src2	    unsigned char *Dest      int
       length	   CODE:	   RETVAL = SDL_imageFilterMultDivby2(Src1, Src2, Dest, length);      OUTPUT:		RETVAL

   mult_div_by_4
       int gfx_image_mult_div_by_4(Src1, Src2, Dest, length)	  unsigned char *Src1	   unsigned char *Src2	    unsigned char *Dest      int
       length	   CODE:	   RETVAL = SDL_imageFilterMultDivby4(Src1, Src2, Dest, length);      OUTPUT:		RETVAL

   bit_and
       int gfx_image_bit_and(Src1, Src2, Dest, length)	    unsigned char *Src1      unsigned char *Src2      unsigned char *Dest      int length
	    CODE:	    RETVAL = SDL_imageFilterBitAnd(Src1, Src2, Dest, length);	   OUTPUT:	     RETVAL

   bit_or
       int gfx_image_bit_or(Src1, Src2, Dest, length)	   unsigned char *Src1	    unsigned char *Src2      unsigned char *Dest      int length
	    CODE:	    RETVAL = SDL_imageFilterBitOr(Src1, Src2, Dest, length);	  OUTPUT:	    RETVAL

   div
       int gfx_image_div(Src1, Src2, Dest, length)	unsigned char *Src1	 unsigned char *Src2	  unsigned char *Dest	   int length
	    CODE:	    RETVAL = SDL_imageFilterDiv(Src1, Src2, Dest, length);	OUTPUT: 	  RETVAL

   bit_negation
       int gfx_image_bit_negation(Src1, Dest, length)	   unsigned char *Src1	    unsigned char *Dest      int length      CODE:
		 RETVAL = SDL_imageFilterBitNegation(Src1, Dest, length);      OUTPUT:		 RETVAL

   add_byte
       int gfx_image_add_byte(Src1, Dest, length, C)	  unsigned char *Src1	   unsigned char *Dest	    int length	    unsigned char C
	    CODE:	    RETVAL = SDL_imageFilterAddByte(Src1, Dest, length, C);	 OUTPUT:	   RETVAL

   add_uint
       int gfx_image_add_uint(Src1, Dest, length, C)	  unsigned char *Src1	   unsigned char *Dest	    int length	    unsigned int C
	    CODE:	    RETVAL = SDL_imageFilterAddUint(Src1, Dest, length, C);	 OUTPUT:	   RETVAL

   add_byte_to_half
       int gfx_image_add_byte_to_half(Src1, Dest, length, C)	  unsigned char *Src1	   unsigned char *Dest	    int length	    unsigned char
       C      CODE:	      RETVAL = SDL_imageFilterAddByteToHalf(Src1, Dest, length, C);	 OUTPUT:	   RETVAL

   sub_byte
       int gfx_image_sub_byte(Src1, Dest, length, C)	  unsigned char *Src1	   unsigned char *Dest	    int length	    unsigned char C
	    CODE:	    RETVAL = SDL_imageFilterSubByte(Src1, Dest, length, C);	 OUTPUT:	   RETVAL

   sub_uint
       int gfx_image_sub_uint(Src1, Dest, length, C)	  unsigned char *Src1	   unsigned char *Dest	    int length	    unsigned int C
	    CODE:	    RETVAL = SDL_imageFilterSubUint(Src1, Dest, length, C);	 OUTPUT:	   RETVAL

   shift_right
       int gfx_image_shift_right(Src1, Dest, length, N)      unsigned char *Src1      unsigned char *Dest      int length      unsigned char N
	    CODE:	    RETVAL = SDL_imageFilterShiftRight(Src1, Dest, length, N);	    OUTPUT:	      RETVAL

   shift_right_uint
       int gfx_image_shift_right_uint(Src1, Dest, length, N)	  unsigned char *Src1	   unsigned char *Dest	    int length	    unsigned char
       N      CODE:	      RETVAL = SDL_imageFilterShiftRightUint(Src1, Dest, length, N);	  OUTPUT:	    RETVAL

   mult_by_byte
       int gfx_image_mult_by_byte(Src1, Dest, length, C)      unsigned char *Src1      unsigned char *Dest	int length	unsigned char C
	    CODE:	    RETVAL = SDL_imageFilterMultByByte(Src1, Dest, length, C);	    OUTPUT:	      RETVAL

   shift_right_and_mult_by_byte
       int gfx_image_shift_right_and_mult_by_byte(Src1, Dest, length, N, C)	 unsigned char *Src1	  unsigned char *Dest	   int length
	    unsigned char N	 unsigned char C      CODE:	      RETVAL = SDL_imageFilterShiftRightAndMultByByte(Src1, Dest, length, N, C);
	    OUTPUT:	      RETVAL

   shift_left_byte
       int gfx_image_shift_left_byte(Src1, Dest, length, N)	 unsigned char *Src1	  unsigned char *Dest	   int length	   unsigned char N
	    CODE:	    RETVAL = SDL_imageFilterShiftLeftByte(Src1, Dest, length, N);      OUTPUT:		 RETVAL

   shift_left_uint
       int gfx_image_shift_left_uint(Src1, Dest, length, N)	 unsigned char *Src1	  unsigned char *Dest	   int length	   unsigned char N
	    CODE:	    RETVAL = SDL_imageFilterShiftLeftUint(Src1, Dest, length, N);      OUTPUT:		 RETVAL

   shift_left
       int gfx_image_shift_left(Src1, Dest, length, N)	    unsigned char *Src1      unsigned char *Dest      int length      unsigned char N
	    CODE:	    RETVAL = SDL_imageFilterShiftLeft(Src1, Dest, length, N);	   OUTPUT:	     RETVAL

   binarize_using_threshold
       int gfx_image_binarize_using_threshold(Src1, Dest, length, T)	  unsigned char *Src1	   unsigned char *Dest	    int length
	    unsigned char T	 CODE:		 RETVAL = SDL_imageFilterBinarizeUsingThreshold(Src1, Dest, length, T);      OUTPUT:
		 RETVAL

   clip_to_range
       int gfx_image_clip_to_range(Src1, Dest, length, Tmin, Tmax)	unsigned char *Src1	 unsigned char *Dest	  int length	  unsigned
       char Tmin      unsigned char Tmax      CODE:	      RETVAL = SDL_imageFilterClipToRange(Src1, Dest, length, Tmin, Tmax);	OUTPUT:
		 RETVAL

   normalize_linear
       int gfx_image_normalize_linear(Src1, Dest, length, Cmin, Cmax, Nmin, Nmax)      unsigned char *Src1	unsigned char *Dest	 int
       length	   int Cmin	 int Cmax      int Nmin      int Nmax	   CODE:	   RETVAL = SDL_imageFilterNormalizeLinear(Src1, Dest,
       length, Cmin, Cmax, Nmin, Nmax);      OUTPUT:	       RETVAL

   convolve_kernel_3x3_divide
       int gfx_image_convolve_kernel_3x3_divide(Src, Dest, rows, columns, Kernel, Divisor)	unsigned char *Src	unsigned char *Dest
	    int rows	  int columns	   Sint16 *Kernel      unsigned char Divisor	  CODE: 	  RETVAL =
       SDL_imageFilterConvolveKernel3x3Divide(Src, Dest, rows, columns, Kernel, Divisor);      OUTPUT:		 RETVAL

   convolve_kernel_5x5_divide
       int gfx_image_convolve_kernel_5x5_divide(Src, Dest, rows, columns, Kernel, Divisor)	unsigned char *Src	unsigned char *Dest
	    int rows	  int columns	   Sint16 *Kernel      unsigned char Divisor	  CODE: 	  RETVAL =
       SDL_imageFilterConvolveKernel5x5Divide(Src, Dest, rows, columns, Kernel, Divisor);      OUTPUT:		 RETVAL

   convolve_kernel_7x7_divide
       int gfx_image_convolve_kernel_7x7_divide(Src, Dest, rows, columns, Kernel, Divisor)	unsigned char *Src	unsigned char *Dest
	    int rows	  int columns	   Sint16 *Kernel      unsigned char Divisor	  CODE: 	  RETVAL =
       SDL_imageFilterConvolveKernel7x7Divide(Src, Dest, rows, columns, Kernel, Divisor);      OUTPUT:		 RETVAL

   convolve_kernel_9x9_divide
       int gfx_image_convolve_kernel_9x9_divide(Src, Dest, rows, columns, Kernel, Divisor)	unsigned char *Src	unsigned char *Dest
	    int rows	  int columns	   Sint16 *Kernel      unsigned char Divisor	  CODE: 	  RETVAL =
       SDL_imageFilterConvolveKernel9x9Divide(Src, Dest, rows, columns, Kernel, Divisor);      OUTPUT:		 RETVAL

   convolve_kernel_3x3_shift_right
       int gfx_image_convolve_kernel_3x3_shift_right(Src, Dest, rows, columns, Kernel, NRightShift)	 unsigned char *Src	 unsigned char
       *Dest	  int rows	int columns	 Sint16 *Kernel      unsigned char NRightShift	    CODE:	    RETVAL =
       SDL_imageFilterConvolveKernel3x3ShiftRight(Src, Dest, rows, columns, Kernel, NRightShift);      OUTPUT:		 RETVAL

   convolve_kernel_5x5_shift_right
       int gfx_image_convolve_kernel_5x5_shift_right(Src, Dest, rows, columns, Kernel, NRightShift)	 unsigned char *Src	 unsigned char
       *Dest	  int rows	int columns	 Sint16 *Kernel      unsigned char NRightShift	    CODE:	    RETVAL =
       SDL_imageFilterConvolveKernel5x5ShiftRight(Src, Dest, rows, columns, Kernel, NRightShift);      OUTPUT:		 RETVAL

   convolve_kernel_7x7_shift_right
       int gfx_image_convolve_kernel_7x7_shift_right(Src, Dest, rows, columns, Kernel, NRightShift)	 unsigned char *Src	 unsigned char
       *Dest	  int rows	int columns	 Sint16 *Kernel      unsigned char NRightShift	    CODE:	    RETVAL =
       SDL_imageFilterConvolveKernel7x7ShiftRight(Src, Dest, rows, columns, Kernel, NRightShift);      OUTPUT:		 RETVAL

   convolve_kernel_9x9_shift_right
       int gfx_image_convolve_kernel_9x9_shift_right(Src, Dest, rows, columns, Kernel, NRightShift)	 unsigned char *Src	 unsigned char
       *Dest	  int rows	int columns	 Sint16 *Kernel      unsigned char NRightShift	    CODE:	    RETVAL =
       SDL_imageFilterConvolveKernel9x9ShiftRight(Src, Dest, rows, columns, Kernel, NRightShift);      OUTPUT:		 RETVAL

   sobel_x
       int gfx_image_sobel_x(Src, Dest, rows, columns)	    unsigned char *Src	    unsigned char *Dest      int rows	   int columns	    CODE:
		 RETVAL = SDL_imageFilterSobelX(Src, Dest, rows, columns);	OUTPUT: 	  RETVAL

   sobel_x_shift_right
       int gfx_image_sobel_x_shift_right(Src, Dest, rows, columns, NRightShift)      unsigned char *Src      unsigned char *Dest      int rows
	    int columns      unsigned char NRightShift	    CODE:	    RETVAL = SDL_imageFilterSobelXShiftRight(Src, Dest, rows, columns,
       NRightShift);	  OUTPUT:	    RETVAL

   align_stack
       void gfx_image_align_stack()	 CODE:		 SDL_imageFilterAlignStack();

   restore_stack
       void gfx_image_restore_stack()	   CODE:	   SDL_imageFilterRestoreStack();

AUTHORS

       See "AUTHORS" in SDL.

perl v5.14.2							    2012-05-28					  pods::SDL::GFX::ImageFilter(3pm)
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