How to check the file type in a script

Question

I want to do a loop for all the images in a directory. The images doesn't have extension so I have to read the first bytes of the image to know its type. The loop should end up being something like.

for file in *
do
    if [ file --mime-type -b ]
    then
        ***
    fi
done

Answer 1

Using the case statement and command substitution :

for file in *; do
    case $(file --mime-type -b "$file") in
        image/*g)        ... ;;
        text/plain)      ... ;;
        application/xml) ... ;;
        application/zip) ... ;;
        *)               ... ;;
    esac
done

Check :
http://mywiki.wooledge.org/BashFAQ/002
http://mywiki.wooledge.org/CommandSubstitution
http://mywiki.wooledge.org/BashGuide/TestsAndConditionals#Choices
http://wiki.bash-hackers.org/syntax/ccmd/case

EDIT

if you insist to don't use case but an if statement using bash :

if [[ $(file --mime-type -b "$file") == image/*g ]]; then
...
else
...
fi