3
_every directory has a parent directory
"the relative pathname for the parent directory is '..'
"the relative pathname for the current directory is '.'
_commands:
"ls, ls -a, ls -al, ls -alt, ls -altr, cd ~/AFNI_data1/afni
"ls -l, wc ideal_r1.1D, cat idea_r1.1D, less ideal_r1.1D
_'less': a file perusal program
"basic keystrokes while running less:  Enter, Space, b, g, G, h, q
"command:  less rall_vr+orig.HEAD
¥Programs
_a program is something that gets "executed", or "run"
_the first element of a command line is generally a program
_commands:
"echo the home directory of $USER is $HOME
"ls ~ ~/AFNI_data1 ~/AFNI_data1/afni/ideal_r1.1D
_script: an interpreted program (interpreted by another program)
"e.g. consider the c00.all script:  cat ~/AFNI_data1/ht03/c00.all