Optimize large-size images for web by interlacing

imgopt.sh

#!/bin/bash
# This program is released under MIT license.
# This program comes with absolutely no warranty and may cause damages, use it at your risk.
# The author of this program is StarBrilliant <echo bTEzMjUzQGhvdG1haWwuY29tCg== | base64 -d>

if [ "$#" -eq 0 ]
then
  echo "Optimize large-size images for web by interlacing"
  echo "Usage: $0 1.png 2.jpg ..."
  echo "optipng and libjpeg are required."
  exit
fi
jpegtran_output=""
jpegtran_output="$(mktemp)"
jpegtran_scans=""
jpegtran_scans="$(mktemp)"
if [ -z "$jpegtran_output" -o -z "$jpegtran_scans" ]
then
  echo 'Fatal: mktemp is unavailable.'
  return 1
fi
cat >"$jpegtran_scans"<<'EOF'
# This file is adapted from jpgcrush
# progressive jpeg scan specification (formatted for `jpegtran -scans`)
# optimized for size, not for actual progressive transmission.
# this averages about 1% smaller than jpegtran's default scan order, and about 1% bigger than image-specific brute-force search.
0:   0  0 0 0 ;
1 2: 0  0 0 0 ;
0:   1  8 0 2 ;
1:   1  8 0 0 ;
2:   1  8 0 0 ;
0:   9 63 0 2 ;
0:   1 63 2 1 ;
0:   1 63 1 0 ;
1:   9 63 0 0 ;
2:   9 63 0 0 ;
EOF
for i in "$@"
do
  basename_i="$(basename "$i")"
  if [ "$(basename "$i" .png)" != "$basename_i" -o "$(basename "$i" .PNG)" != "$basename_i" ]
  then
    echo "optipng -i1 $i"
    optipng -i1 "$i"
  elif  [ "$(basename "$i" .jpg)" != "$basename_i" -o "$(basename "$i" .JPG)" != "$basename_i" -o "$(basename "$i" .jpeg)" != "$basename_i" -o "$(basename "$i" .JPEG)" != "$basename_i" ]
  then
    true >"$jpegtran_output"
    echo "jpegtran -copy all -optimize -progressive -scans "$jpegtran_scans" -outfile $jpegtran_output $i"
    jpegtran -copy all -optimize -progressive -scans "$jpegtran_scans" -outfile "$jpegtran_output" "$i"
    if [ "$?" -eq 0 ]
    then
        echo "mv $jpegtran_output $i"
        mv "$jpegtran_output" "$i"
    fi
  else
    echo "Error: unsupported file, only *.png, *.jpg, *.jpeg are supported."
  fi
done
rm -f "$jpegtran_output" "$jpegtran_scans"

Stylecheck...

• [ ... -o ] is not POSIX and not readable. Since you are using bash, I suggest using [[ ... || ... ]]. Otherwise [ ... ] || [ ... ].
• Using basename to remove suffixes is not interesting. Since you seem like trying to do some pattern matching, why not use case? *.[pP][nN][gG] works perfectly (so does *.png|PNG.)
  • As an aside, bash [[ can be used for glob matching: [[ $a == *.avi.?z ]] matches aaa.avi.gz and aaa.avi.xz. != works too.
  • You can get regex-grade globbing power by enabling extglob.
• Quote screw-up on :48. Try set -x and set +x?

StaticChk...

• Dead code :13 :15.
• non-function return :20.