On May 31, 2018, at 14:40, Stephen via talk <talk@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