C shell commands

A simple command is a sequence of words separated by blanks or tabs. A word is a sequence of characters or numerals, or both, that does not contain blanks without quotation marks.

&       |      ;        
&&      ||    <<        > >
<       >     (          )

These special characters can be parts of other words. Preceding them with a backslash (\), however, prevents the shell from interpreting them as special characters. Strings enclosed in ' ' or " " (matched pairs of quotation characters) or backquotes can also form parts of words. Blanks, tab characters, and special characters do not form separate words when they are enclosed in these marks. In addition, you can enclose a newline character within these marks by preceding it with a backslash (\).

The first word in the simple command sequence (numbered 0) usually specifies the name of a command. Any remaining words, with a few exceptions, are passed to that command. If the command specifies an executable file that is a compiled program, the shell immediately runs that program. If the file is marked executable but is not a compiled program, the shell assumes that it is a shell script. In this case, the shell starts another instance of itself (a subshell) to read the file and execute the commands included in it.