Reading a variable line by line with while loop

[Ray Parrish]

Ray Parrish wrote:
> PleegWat wrote:
>   
>> Alan McKay wrote:
>>   
>>     
>>>> echo "$Variable" | while read
>>>> ...
>>>> done
>>>>
>>>>    has better chances of working.
>>>>       
>>>>         
>>> This method has gotchas though, and I try to avoid it.  The pipe
>>> causes the while to execute in a sub shell and so any variable changes
>>> you make inside the loop will be lost when you get out of the loop.
>>> For this reason I often actually create a file and do the redirect as
>>> per the original post
>>>
>>> e.g.
>>>
>>> while stuff
>>> do
>>> done < file
>>>     
>>>       
>> Another (bash-specific) solution:
>>
>> while condition
>> do stuff
>> done < <(command)
>>
>> The <(command) construct runs `command`, redirects stdout to a pipe, and 
>> returns the name of the named pipe.
>>
>> This construct has the disadvantages of being bash-specific and 
>> resulting in hard-to-read code.
>>
>> Two more solutions specifically for input from a variable: Heredoc
>>
>> while condition
>> do stuff
>> done <<EOF
>> $variable
>> EOF
>>
>> Or herestring (bash-specific)
>>
>> while condition
>> do stuff
>> done <<< "$variable"
>>
>> PleegWat
>>   
>>     
> Hello again,
>
> Well, I'm making some progress. I have the following code which works to 
> a point.
>
>      while read ThisCommand; do
>            ThisCommand=${ThisCommand// /__};
>            if `echo "${History}" | grep "${ThisCommand}" 1>/dev/null 2>&1`
>                then
>                    echo "nothing" >/dev/null
>                else
>                    History="$History $ThisCommand";
>            fi
>      done < <(cat ~/.bash_history)
>      Command=`Xdialog --stdout --title "Ray's Bash Manager - Select 
> Command to Copy" --cancel-label "Exit" --combobox "Select a Command to 
> Copy to the Clipboard." 0 60 $History`
>
> The if statement is meant to catch duplicate lines, and it does, unless 
> they contain quotes in them, and then they get duplicated in the output. 
> Is there some way to trap even the lines with quotes in them?
>
> Thanks again, Ray Parrish
>   
Hello again,

I have found an if statement that reduces the duplicates to only two 
pairs for the entire file. That's pretty good considering the number of 
actual duplicates there were in the file to begin with. Here is the code 
for that one -

function CompressHistory {
     BashHistory=`cat ~/.bash_history`
     while read ThisCommand; do
           ThisCommand=${ThisCommand// /__};
           if  [[ "$History" =~ "$ThisCommand" ]]
               then
                   echo "nothing" >/dev/null
               else
                   History="$History $ThisCommand";
           fi
     done <<< "$BashHistory"
     echo "$History"
}

This next bit of code has me frazzled trying to figure out the proper 
regular expression to say "if this string exists within the larger 
string". Nothing I have tried so far has worked, so here is the code, 
and maybe someone can correct my regular expression so it works to weed 
out duplicates as well.

     BashHistory=`cat ~/.bash_history`
     while read ThisCommand; do
           ThisCommand=${ThisCommand// /__};
           if  [[ "$History" == [.]*$ThisCommand[.]* ]]
               then
                   echo "nothing" >/dev/null
               else
                   History="$History $ThisCommand";
           fi
     done <<< "$BashHistory"

 From what I have read the dot is supposed to match any character, and 
then the * specifies that any number of characters can appear in that 
position. I'm just realizing that would specify perhaps one character 
only, repeated to the ends of the large string before it would match.

I do not know how to specify that the whole front, and the whole back of 
the variable should be the same with the matching string in the middle 
of them.

Thanks again for any help you can be. Later, Ray Parrish

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