How to set icon on file or directory using CLI on OS X?

Question

To set an icon on a file or directory is straight forward using the \"Get Info\" dialog in Finder.

1. copy image from e.g. Preview
2. open \"Get Info\" on

Answer 1

Here is a bash script "setIcon.sh" for it

#!/bin/sh
# Sets an icon on file or directory
# Usage setIcon.sh iconimage.jpg /path/to/[file|folder]
iconSource=$1
iconDestination=$2
icon=/tmp/`basename $iconSource`
rsrc=/tmp/icon.rsrc

# Create icon from the iconSource
cp $iconSource $icon

# Add icon to image file, meaning use itself as the icon
sips -i $icon

# Take that icon and put it into a rsrc file
DeRez -only icns $icon > $rsrc

# Apply the rsrc file to
SetFile -a C $iconDestination

if [ -f $iconDestination ]; then
    # Destination is a file
    Rez -append $rsrc -o $iconDestination
elif [ -d $iconDestination ]; then
    # Destination is a directory
    # Create the magical Icon\r file
    touch $iconDestination/$'Icon\r'
    Rez -append $rsrc -o $iconDestination/Icon?
    SetFile -a V $iconDestination/Icon?
fi

# Sometimes Finder needs to be reactivated
#osascript -e 'tell application "Finder" to quit'
#osascript -e 'delay 2'
#osascript -e 'tell application "Finder" to activate'

rm $rsrc $icon

Answer 2

Assuming that we have icns-file already. Create temp resource file which points to icns-file:

$ echo "read 'icns' (-16455) \"Icon.icns\";" >> Icon.rsrc

Append the resource file as value of extended attribute "com.apple.ResourceFork" to a file:

$ Rez -a Icon.rsrc -o FileName.ext

Show the icon of the file:

$ SetFile -a C FileName.ext

Append resource file as value of extended attribute "com.apple.ResourceFork" to a magic icon file inside current folder:

$ Rez -a Icon.rsrc -o Icon$'\r'

Show the icon of current folder:

$ SetFile -a C .

Hide the magic icon file inside current folder (press ⇧⌘. to show/hide hidden files in Finder):

$ SetFile -a V Icon$'\r'

Additional details

Icon data is stored as value of extended attribute "com.apple.ResourceFork" (Terminal command "xattr -p com.apple.ResourceFork FileName.ext" prints the value). For a folder there is magic (which is empty and hidden) file Icon$'\r' inside the folder. To extract icon data from extended attribute "com.apple.ResourceFork" into plain text resource file (from which we know correct icns-type identifier "-16455"):

$ DeRez -only icns FileWithIcon.ext > Icon.rsrc
$ DeRez -only icns /Folder/With/Icon/Icon$'\r' > Icon.rsrc

Under macOS 10.13 High Sierra command $ sips -i ImageFile.icns/png/jpg generates error --addIcon is no longer supported. Switch -i means "--addIcon" as extended attribute "com.apple.ResourceFork" onto this file itself using the content of this image file.