find

find . -name "*" -exec grep -Hn "spam" {} \; | grep -v svn 

This doesn't display all the svn revisions

(or just use grep . "spam" -R)

find files without error messages

find . -name *  2>/dev/null                                            

find all the files containing "spam"

find . -name "*" -exec grep -sHIrin "spam" --directories=skip {} \;

find . -type l -xtype l

between two dates

find * -type f -mtime -65 -mtime -64
find * -type f -mtime -65 -mtime -64 -print0|xargs -0 grep -l toto

find the number of days between today and another day

a=$(date -d "20160615" +%s);b=$(date +%s); echo $((($b-$a)/(24*3600)))