Bash timestamp comparisions

Question

Im completely new to Bash scripting but I've been told, with little help, to create a file that compresses textures into PVR format only if the file has been modified since the last time the script was run. Heres the code I have so far:

# variables
TEXTURE_TOOL=/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/texturetool
INPUT_DIR="/Data/Mobile"
OUTPUT_DIR="/Data/iPhone"
IMAGE_GREP="\(.bmp\|.png\)"
OTHER_GREP="\.b3d$"

echo "Starting backup of directory $INPUT_DIR to directory $OUTPUT_DIR"

# cycle through the input directory for images we can compress
echo "Compressing textures!"
for i in $( ls -a "$INPUT_DIR" | grep $IMAGE_GREP  ); 
     do
        if test "$OUTPUT_DIR/$i.pvr" -nt "$INPUT_DIR/$i"; then
     # check to see output's status
     echo "Compressing file $i!"

     # compress and store in output directory
     $TEXTURE_TOOL -m -e PVRTC --bits-per-pixel-2 -o "$OUTPUT_DIR/$i.pvr" -f PVR "$INPUT_DIR/$i"
        fi
     done

# cycle through the input directory for models we can export
echo "Moving models!"
for i in $( ls -a "$INPUT_DIR" | grep $OTHER_GREP  ); 
     do
     # check to see output's status
     echo "Moving model file $i!"

     # cp to output directory
     cp "$INPUT_DIR/$i" "$OUTPUT_DIR/$i"
     done

Using one of the questions here I tried to do the timestamp checking but I it isnt working and I'm pretty sure its because I dont fully understand the code.

Can anyone suggest what Im doing wrong

Thanks, Michael A

Answer 1

test "$OUTPUT_DIR/$i.pvr" -nt "$INPUT_DIR/$i";

Checks to see if $OUTPUTDIR/$i.pvr is newer than $INPUTDIR/$i, I think you want to do it the other way around.

test "$INPUT_DIR/$i" -nt "$OUTPUT_DIR/$i.pvr";

To check to see fi the input is newer than the output.

Answer 2

Doing things only if some files are newer than expected is best achieved with make. This is a little more complex to learn but very efficient.