The Most Important Tools (1/2)

cat
conCATenate several files (neutral element of pipe operator)

grep
Global Regular Expression Printer, estracts file lines

ls, cp, mv,    chmod, chown, ln, mknod, mkfifo    df, du, wc
manage files, their metadata, their size

echo, pwd, touch, yes, true, false, tee
trivial but very useful programs

less
a pager, to look at file contents (less is better than more)

test, [
evaluates a conditional, used in "if" and "while" loops