[GTALUG] Help need in bash

[Stephen]

That is what I needed. Thank you!

On 2018-05-31 04:47 PM, Seneca Cunningham via talk wrote:
> 
>> On May 31, 2018, at 14:40, Stephen via talk <talk at gtalug.org> wrote:
>>
>> I want to build a script to convert any *.png files to *.jpg files using convert.
>>
>> Doing manually works fine.
>>
>> Building a script has presented problem. I am well versed in programming but a novice with bash.
>>
>> My loop through the files works fine.
>>
>> #!/bin/bash
>> cd /big1/memes/;
>>
>> shopt -s nullglob
>> for f in "*.png"
>> do
>>     echo $f
>> done
>>
>> I get a list of filenames with an extension of .png
>>
> 
> In this case, the value of $f is ‘*.png’.  Your loop iterates once, and the list of PNG files is generated as a shell expansion before evaluating the “echo”.
> 
>> But when I try to get the basename with:
>>
>> #!/bin/bash
>> cd /big1/memes/;
>>
>> shopt -s nullglob
>> for f in "*.png"
>> do
>>     echo $f
>>     b=${f%.png}
>>     echo $b
>> done
>>
>> I first get a list of the .png files, then a list of all files, both the existing .jog and the .png. This gets a WTF reaction from me.
> 
> Once more, $f is ‘*.png’ and is being expanded for the execution of the echo.  Your brace expansion looks to be converting ‘*.png’ to the string ‘*’, and assigning that to b.  The when evaluating the line “echo $b”, the value of $b, ‘*’, is expanded prior to execution.
> 
>> Can someone explain and help me get closer to getting this to work?
> 
> You were a touch sloppy with your quoting.  You should have left “*.png” unquoted in the for loop so that the list of file names to process would expand there, and stuck $f and $b in double quotes so their values would not expand.
> 
> Seneca
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-- 
Stephen