converting multiple files

converting multiple PNG files to PNG files with a width of 400 pixels

for i in !(*-small.png) ; do if test ! -s "${i%.*}-small.png" ; then convert "$i" -resize '400' "${i%.*}-small.png" ; fi ; done

converting multiple TIFF files to PNG files

In the current directory, each file with the .tiff file extension not already accompanied by a file with .png in place of .tiff or -intermediate.png in place of .tiff will be converted into two PNG files.

for i in *.tiff ; do if { test ! -s "${i%.*}-intermediate.png" && test ! -s "${i%.*}.png"; } ; then convert "$i" "${i%.*}-intermediate.png" && pngcrush "${i%.*}-intermediate.png" "${i%.*}.png" ; fi ; done

explanation

Note

This is an incomplete explanation.

• *-small.png uses the asterisk (*) special character for filename expansion, matching every filename ending in -small.png.
• The -resize '400' option changes the image geometry to a width of 400 pixels.

prior work

• The test command was introduced to me by a comment on a question I asked on Stack Overflow by fmw42.
• The bulk of the contents of the script's for-loop construct was introduced to me by an answer on Super User by Kevin Cox.
• The bulk of the contents of the script's if-construct was introduced to me by the test (Unix)§Examples page on Wikipedia.
• The correct syntax for the if-contruct was introduced to me by an answer on Stack Overflow by Shawn Chin.

licensing

Some rights reserved: CC BY-SA 3.0. Includes significant content from an answer on Super User by Kevin Cox and test (Unix)§Examples on Wikipedia, with changes made.