Rename a pile of files

        for F in tt_*
        do
                mv $F pe` expr $F : 'tt\(.*\)' `
        done

or

        for F in tt_*
        do
                mv $F pe_`echo $F | sed 's;tt_\(.*\);\1;'`
        done

or

        for F in tt_*
        do
                mv $F ` echo $F | sed 's-tt-pe-' `
        done



How about just within the KornShell ? ? ?

If the user's shell is /bin/ksh, then, from the command line, just:


  for F in tt_* ; do mv $F pe_${F#*_} ; done


If the user's shell is not /bin/ksh, then, from the command line, just:

  ksh
  for F in tt_* ; do mv $F pe_${F#*_} ; done ; exit


Or a shell script executed from any shell:

  #!/bin/ksh
  for F in tt_* ; do mv $F pe_${F#*_} ; done


What's the use of calling 'expr', 'sed', 'awk', 'cut', etc. a number
of times when it can be done all within the shell itself?


Show your PATH


One solution  found on comp.unix.shell the other week that's nicely 
compact (and is an interesting exercise in shell expansion!) is (for ksh):


TILDE='~'
PS1='${TILDE[(1-0${PWD%%@([!/]*|$HOME*)}1)]-}${PWD#$HOME}$ '


This will replace $HOME with ~ if its in $PWD (and is the only one (and change)
liner I've seen that will do this :)