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 Forum index » Off-Topic Area » Programming
trailing whitespace (Solved)
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don570


Joined: 10 Mar 2010
Posts: 5345
Location: Ontario
PostPosted: Wed 27 Dec 2017, 18:19    Post subject:  trailing whitespace (Solved)  
There is a strange behaviour I noticed with trailing whitespace.
The following isn't successful...

Code:
# A="Note: ";[ $A = "Note: " ] &&  echo successful



If I assume that there is no trailing whitespace....

Code:

# A="Note: ";[ $A = "Note:" ] &&  echo successful
successful

An extra layer of brackets also solves the problem....
Code:

# A="Note: ";[[ $A = "Note: " ]] &&  echo successful
successful
 


______________________________________________________

I checked with a gtkdialog script and there doesn't appear to be any
problem with trailing whitespace.

Code:

#!/bin/bash
# whitespace experiment

export DIALOG='<window>
 <vbox>
 

 <frame>
<hbox> 
  <entry>
        <default>"Note: "</default>

    <variable>MESSAGE</variable>
  </entry>
</hbox>
</frame>
<button ok>             
      </button>      

 </vbox>
 </window>
'
 I=$IFS; IFS=""
     for STATEMENTS in  $(gtkdialog --geometry=+200+100 --program DIALOG); do
       eval $STATEMENTS       
     done
# check for trailing  whitespace     
   
A="$MESSAGE";[ $A = "Note: " ] &&  xmessage success


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MochiMoppel


Joined: 26 Jan 2011
Posts: 1897
Location: Japan
PostPosted: Wed 27 Dec 2017, 22:10    Post subject: Re: trailing whitespace  
don570 wrote:
The following isn't successful...
Code:
# A="Note: ";[ $A = "Note: " ] &&  echo successful

A="Note: ";[ "$A" = "Note: " ] && echo successful

Quote:
I checked with a gtkdialog script and there doesn't appear to be any problem with trailing whitespace.
...because you didn't change $IFS back to its default value.
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don570


Joined: 10 Mar 2010
Posts: 5345
Location: Ontario
PostPosted: Fri 29 Dec 2017, 16:18    Post subject:  
Quote:
you didn't change $IFS back to its default value


I hadn't thought about IFS. Embarassed
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don570


Joined: 10 Mar 2010
Posts: 5345
Location: Ontario
PostPosted: Tue 02 Jan 2018, 13:42    Post subject:  
I need to read more about IFS. It's mentioned in.
Advanced Bash Manual
_____________________________________________________
________________________________________________________

Code:
$IFS defaults to whitespace (space, tab, and newline), but may be changed, for example, to parse a comma-separated data file. Note that $* uses the first character held in $IFS. See Example 5-1.

bash$ echo "$IFS"

(With $IFS set to default, a blank line displays.)
        


bash$ echo "$IFS" | cat -vte
 ^I$
 $
(Show whitespace: here a single space, ^I [horizontal tab],
  and newline, and display "$" at end-of-line.)



bash$ bash -c 'set w x y z; IFS=":-;"; echo "$*"'
w:x:y:z
(Read commands from string and assign any arguments to pos params.)
        

Set $IFS to eliminate whitespace in pathnames.

IFS="$(printf '\n\t')"   # Per David Wheeler.
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don570


Joined: 10 Mar 2010
Posts: 5345
Location: Ontario
PostPosted: Tue 02 Jan 2018, 13:44    Post subject:  
I noticed that someone has put up a good page with examples to
explain gtkdialog
http://xpt.sourceforge.net/techdocs/language/gtkdialog/gtkde02-GtkdialogExamples/
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