Don't understand the practical difference between command aliases and environmental variables
Hey,
I'm recently learning Unix from the video course by Kevin Scoglund. I'm stuck at the moment where he goes into Environmenat variables. I have some issues with understanding what's the essential difference between EV and command aliases: for instance, by writing the command
Code:
alias ll='ls -lahG'
into .bashrc file we ensure that typing every time the shortcut ll we get the whole bunch of modifications to the original command executed whenever we type it.
ALong with that we have so called "environmental variables" (f.e., export LESS='-N') we could equal to any value ("variable") that theoretically when saved to .bashrc should trigger that command exactly as we predefined it.
According to Mr. Scoglund it should work once we launch another Terminal session by opening a new window ir by executing
Code:
source .bashrc
. However, when trying the former it fails to do so (no command found), so I have to rely on the latter which is pain in the ass typing it in every time. It should be mentioned he worked with Snow Leopard while I'm on Lion, so definitely some changes occurred here.
So:
(1) I can't execute .bashrc file commands unless I execute
Code:
source .bashrc
Is there less labourous method of doing that without
Code:
source .bashrc
in Lion?
(2) what's the point of EV since one could assign an alias to a command and the result is pretty much the same?
If I sound dumb forgive me since I was forced to skip that entire chapter about profile, login and resource files due to corrupted video file containing that part so I might have missed some points completely hence is my confusion.
Last edited by scrutinizerix; 01-10-2016 at 07:29 AM..
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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)
01-09-2016
so I might have missed some points completely hence is my confusion.