IF statement with square brackets Post: 302983621

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Top Forums Shell Programming and Scripting IF statement with square brackets Post 302983621 by mad man on Friday 14th of October 2016 02:41:49 AM

10-14-2016

Registered User

IF statement with square brackets

Hi All,

Hope you all are doing good. Yesterday in my project i came across a scenario which i can not guess why it was working in one region and why it was not in another region. Please find my issue below.

I am using AIX version 6.0 of UNIX in my project, in shell scripting i have the following code to check if a file exists in a directory or not.

Code:

       
if [ -f $com_dir/$dup_file_name_chk ] || 
[ -f $save_dir/$dup_file_name_chk ]
then
.
.
.
fi

I tested this code in the development region every thing went fine and moved the code to QA there also testing went fine. After 2 successful tests the code was moved to UAT region, my onsite manager tested it in UAT and found this is not working, the file existence was not detected there and testing failed.

After this i doubted this if condition and made it like below.

Code:

       
if [[ -f $com_dir/$dup_file_name_chk ]] || 
[[ -f $save_dir/$dup_file_name_chk ]]
then
.
.
.
fi

Now the same was tested in dev, QA & UAT regions. Now this file existence check was working in UAT region.

Can anyone explain what made this '[[' double brackets to work in the UAT region instead of '[' single bracket. What is the difference between them?
Also why regions differ(single brackets working in dev & QA not in UAT).

mad man

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xsubtractregion

XIntersectRegion(3)						  XLIB FUNCTIONS					       XIntersectRegion(3)

NAME

       XIntersectRegion, XUnionRegion, XUnionRectWithRegion, XSubtractRegion, XXorRegion, XOffsetRegion, XShrinkRegion - region arithmetic

SYNTAX

       int XIntersectRegion(Region sra, Region srb, Region dr_return);

       int XUnionRegion(Region sra, Region srb, Region dr_return);

       int XUnionRectWithRegion(XRectangle *rectangle, Region src_region, Region dest_region_return);

       int XSubtractRegion(Region sra, Region srb, Region dr_return);

       int XXorRegion(Region sra, Region srb, Region dr_return);

       int XOffsetRegion(Region r, int dx, int dy);

       int XShrinkRegion(Region r, int dx, int dy);

ARGUMENTS

       dest_region_return
		 Returns the destination region.

       dr_return Returns the result of the computation.  ds Dy move or shrink

       dx
       dy	 Specify the x and y coordinates, which define the amount you want to  the specified region.

       r	 Specifies the region.

       rectangle Specifies the rectangle.

       sra
       srb	 Specify the two regions with which you want to perform the computation.

       src_region
		 Specifies the source region to be used.

DESCRIPTION

       The XIntersectRegion function computes the intersection of two regions.

       The XUnionRegion function computes the union of two regions.

       The XUnionRectWithRegion function updates the destination region from a union of the specified rectangle and the specified source region.

       The XSubtractRegion function subtracts srb from sra and stores the results in dr_return.

       The XXorRegion function calculates the difference between the union and intersection of two regions.

       The XOffsetRegion function moves the specified region by a specified amount.

       The XShrinkRegion function reduces the specified region by a specified amount.  Positive values shrink the size of the region, and negative
       values expand the region.

SEE ALSO

       XCreateRegion(3), XDrawRectangle(3), XEmptyRegion(3)
       Xlib - C Language X Interface

X Version 11							   libX11 1.5.0 					       XIntersectRegion(3)