The grep command serves in shell scripting and in OS command lines to filter out relevant ASCII data from standard input. It's best used in conjunction with pipes.
The dot '.' is a basic wildcard that will stand for any character. For example
> ll | grep d.t
will list all lines containing dat, dut, dit, dot, etc... The following will look for any line containing hello.gif:
> ll | grep 'hello\.gif'
For example, the following command will only display the files containing a .dat extension.
> ls -l | grep .dat
Here's the same example for dos (windows)
> dir /B | grep .dat
The following example lists only directories (i.e. everything but lines ending with '.????' or '.???' or '.??')
$ dir /B /S | grep "[^.]....$" | grep "[^.]...$" | grep "[^.]..$"
> find . | grep '[^.]....$' | grep '[^.]...$' | grep '[^.]..$'
Here's another example that lists every hdf5 file except the InterfaceSedimentWater
> find . | grep '.hdf5$' | grep '^...........[^S]'
Here's an example that lists everything except the pattern
> find .| grep '\.f90' | grep -v 'GOTMvariables'
This example will show only the crond daemon
> ps -aux | grep crond