Reading a variable line by line with while loop

[Ray Parrish]

Ray Parrish wrote:
> Loïc Grenié wrote:
>   
>> 2009/12/1 Ray Parrish <crp at cmc.net>:
>>   
>>     
>>> Hello,
>>>
>>> I have been using while loops to read files in line by line when I want
>>> to process things on a line oriented basis. Sometimes i have the set of
>>> lines I want to read through already in a variable, and have to write
>>> them to file before beginning to read line by line.
>>>
>>> I was wondering if it is possible to read a variable line by line
>>> somehow with a while loop? Would it possibly be faster than using a file
>>> to read from?
>>>
>>> I was thinking something along the lines of the following code might
>>> work, but have not tested it yet.
>>>
>>> while read ThisLine; do
>>>      # process each line
>>>      echo "$ThisLine"
>>> done < `echo "$Variable"`
>>>
>>> Is this something that might work, and would it be more efficient than
>>> writing to, and reading from a file? Is there some other way I've missed
>>> to make it work?
>>>     
>>>       
>>     This will probably not work.
>>
>> echo "$Variable" | while read
>> ...
>> done
>>
>>     has better chances of working.
>>
>>            Loïc
>>   
>>     
> Well, that one test worked, but I cannot get the following to work -
>
> # Read bash history into a variable for use with combobox call
> History=""
> BashHistory=`cat ~/.bash_history`
> echo "$BashHistory" | while read ThisCommand; do
>      # Replace spaces in each command line with __ [double underlines]
>      ThisCommand=${ThisCommand// /__}
>      # Concatenate the results to the Command variable
>      History="$History $ThisCommand"
> done
> echo "History - $History"
>
> The last echo command returns nothing, but if I put an echo command in 
> the loop either before, or after the replace spaces command, it echoes 
> every line of the variable to the console.
>
> Does anyone have any idea why it's not working because I am stumped...
>
> Later, Ray Parrish
>   
Hello again,

OK, I understand that the | is causing a sub shell to execute for the 
echo command, so the variable $History even 'though declared globally, 
is local to the loop with the pipe, and therefore not available after 
the loop exits.

I have tested this by putting an echo "History - $History" command right 
after the concatenation line in the loop. This causes some pretty slow 
execution as the extremely long string get echoed over and over again, 
but showed that the variable was indeed getting updated each time 
through the loop.

Does anyone know how to fix my code so it can access the value of the 
$History variable after the loop exits?

Thanks again, Ray Parrish

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