Unix hacker stuff

Here’s a one-liner to print the aspect ratios of all the JPEG images in a directory.  I’ve broken it up onto multiple lines here, just for readability:

for f in *.jpg; do {
echo -n "$f  "; identify $f
|grep -oE "[0-9]+x[0-9]+"
|sed ’s!\(.*\)!scale=3;\1!’
|sed ’s!x!/!’|bc;
} done

(You can also substitute [[:digit:]] for [0-9].)

What it does:

• the identify command (from the ImageMagick package) prints info about the JPEG, including its dimensions as XxY, which we grep out.

• we use sed to prepend "scale=3;" so that bc prints 3 decimal places.

• sed again to change XxY to X/Y.

• pass "scale=3; X/Y" to bc, the command-line calculator, to perform the division.

Requires just ImageMagick, sed, and of course bash, all of which are present on most modern Unixes and Linuxes.