for command

[Tyler Spivey]

an example: to tail all the files in the current directory,
you can do tail *, also:
for i in *; do tail $i;done
you can do (in bash):
help for
and it gives you:
for: for NAME [in WORDS ... ;] do COMMANDS; done
    The `for' loop executes a sequence of commands for each member in a
    list of items.  If `in WORDS ...;' is not present, then `in "$@"' is
    assumed.  For each element in WORDS, NAME is set to that element, and
    the COMMANDS are executed.
so,
for i in *.txt;do cat "testing" >>$i;done
would append "Testing" to the files in the current directory ending with .txt.
hope this helps.