shellcheck fixes in 2020/kurdyukov2

try.sh now runs makegif.sh.

Fix makegif.sh to first compile the program, allow one to specify CC and
convert and check that the output file was created. In the case
convert(1) is not found or it fails to generate the output file it
suggests the user look at the FAQ entry about ImageMagick.

2020/kurdyukov2/try.sh

@@ -27,6 +27,8 @@ convert_error()
     echo 1>&2
 }
 
+# remove ppm files that we create
+rm -f random.ppm output.ppm
 echo "$ (echo P6 1024 1024 255; dd if=/dev/urandom bs=3M count=1) > random.ppm" 1>&2
 (echo P6 1024 1024 255; dd if=/dev/urandom bs=3M count=1) > random.ppm
 echo "Look at random.ppm. Do you see any patterns?" 1>&2
@@ -54,8 +56,13 @@ if [[ -n "$CONVERT" ]]; then
     echo 1>&2
     read -r -n 1 -p "Press any key to create GIF: "
     echo 1>&2
-    echo "$ $CONVERT -delay 10 -dither none -loop 0 $(ls out*.jpg | sort -V) $(ls out*.jpg | sort -rV) +map out.gif" 1>&2
-    "$CONVERT" -delay 10 -dither none -loop 0 $(ls out*.jpg | sort -V) $(ls out*.jpg | sort -rV) +map out.gif
+    echo "$ $CONVERT -delay 10 -dither none -loop 0 $(find . -maxdepth 1 -type f -name '*jpg' | sort -V) $(find . -maxdepth 1 -type f -name '*jpg' | sort -rV) +map out.gif" 1>&2
+    # We want word splitting here so disable shellcheck warning SC2046.
+    #
+    # SC2046 (warning): Quote this to prevent word splitting.
+    # https://www.shellcheck.net/wiki/SC2046
+    # shellcheck disable=SC2046
+    "$CONVERT" -delay 10 -dither none -loop 0 $(find . -maxdepth 1 -type f -name '*jpg' | sort -V) $(find . -maxdepth 1 -type f -name '*jpg' | sort -rV) +map out.gif
     if [[ ! -f out.gif ]]; then
 	convert_error
     else
@@ -63,6 +70,11 @@ if [[ -n "$CONVERT" ]]; then
 	echo "Now look at out.gif with a graphics viewer that can show animated GIFs." 1>&2
 	echo "Warning: includes flashing colours." 1>&2
     fi
+
+    read -r -n 1 -p "Press any key to run: ./makegif.sh sample.jpg kurdyukov2.gif ./prog: "
+    echo 1>&2
+    ./makegif.sh sample.jpg kurdyukov2.gif ./prog
+    echo 1>&2
 else
     echo 1>&2
     echo "Could not fine convert(1) from ImageMagick." 1>&2