UNIX IX: Advanced Shell Commands

• Pipes allow you to connect the output of one program to the input of another, and are denoted by the "|" character. For example, ls | more sends the output of ls through the more program. This is useful if you have lots of files in a directory.

• What does ls | lpr do?

• Wildcards allow you to run a command on all the files in a directory matching certain criteria. The wildcard "*" matches any sequence of letters and the wildcard "?" matches any single character. For example, rm *.c removes all the files in the current directory ending in ".c".

• What does mv *.bak /tmp do?

• UNIX is a multitasking operating system and allows you to have several programs running at once. These programs are divided into foreground tasks which have the ability to do input/output from a terminal (or xterm) and background tasks which don't.
  • To run a program foobar in the background, just type foobar &.
  • To move the current foreground task in the background, type Control-Z.
  • To see which programs are running, type jobs.
  • To move a background task in the foreground, type fg %(job number) .

• Finally, shells allow you to redirect where the input and output come from and go to. Typing command > filename tells command to put its output into filename. Similarly, typing command < filename tells command to take its input from filename.