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Oneliner bash built-in (doesn't work for repetition):

DIR=/dir/to/remove PATH=${PATH/${PATH/#$DIR:*/$DIR:}/}${PATH/${PATH/*:$DIR*/:$DIR}/} 

Oneliner bash built-in:

DIR=/dir/to/remove PATH=${PATH/${PATH/#$DIR:*/$DIR:}/}${PATH/${PATH/*:$DIR*/:$DIR}/} 

• Uses recursive shell parameter expansion to remove colon before or after removed directory
• Pattern has two halves. One half is always empty, other provide reduced path.
• Removes just one instance of $DIR from $PATH

Oneliner bash built-in (doesn't work for repetition):

export DIR=/dir/to/remove PATH=${PATH/${PATH/#$DIR:*/$DIR:}/}${PATH/${PATH/*:$DIR*/:$DIR}/} 

Oneliner bash built-in (doesn't work for repetition):

DIR=/dir/to/remove PATH=${PATH/${PATH/#$DIR:*/$DIR:}/}${PATH/${PATH/*:$DIR*/:$DIR}/} 

Oneliner bash built-in (doesn't work for repetition):

PATH=${PATH/${PATH/#$DIR:*/$DIR:}/}${PATH/${PATH/*:$DIR*/:$DIR}/}

Oneliner bash built-in (doesn't work for repetition):

export DIR=/dir/to/remove PATH=${PATH/${PATH/#$DIR:*/$DIR:}/}${PATH/${PATH/*:$DIR*/:$DIR}/}