Linux Commands

• Small utilities/programs under Linux that can take options and arguments.
• The executable (binary) for most of them can be found in /usr/bin.
• Argument: what the command applies to. ls /usr
• Option: how do we want the command to be executed
  ls –l
• Usual commands: ls, man, cat, less, cd, mkdir.
• The find command: the argument is a path. The name of the file must be specified with the option –name:
  find ./ -name hw1.txt

Some Commands

• The commands start with the name of the executable (binary), followed by options (-letter) and/or arguments.
• Example:
  ls -l /usr/include
  -l is an option meaning use a long listing format
  /usr/include is an argument
• Some useful commands:
  cd, ls, man, less, cat
  grep, find, wc,
• Manipulating files and directories:
  mv, rm, cp, mkdir, rmdir
• Information about the file system:
  quota, du, df

More On Commands

• The options and arguments can be combined:
  ls -l /usr/include
• -l is an option meaning use a long listing format
  
• /usr/include is an argument
• Some useful commands:
  cd, ls, man, less, cat
  grep, find, wc,
• Manipulating files and directories:
  mv, rm, cp, mkdir, rmdir
• Information about the file system:
  quota, du, df
• Some commands take more than one argument: cp requires a source file and a destination file.

Expressions in Commands

• Current directory: .
• Parent directory: ..
• Home directory: ~
• Designating file/path names using a pattern:
  the wildcard * can be matched by anything: ls ./a* lists all the files in the current directory starting with an a.

Linux Processes

• A process is any running program.
• Under Linux a process has an identity (PID), a parent process (PPID), an owner (UID).
• To view the active processes: ps
  Useful options: -A (all), -l (long list)
  Also: top
• Stop the execution of a program launched from a terminal: Ctrl-c
• Stop the execution of any process: kill. The argument must be the process id.
• The kill command send signals to processes. The signal 9 is the most powerful.
  kill -s 9 1258

Launching Jobs on Linux

• A job is any executable run from the terminal.
• The jobs can be piped: the content of one can be sent to the next with the symbol | in between.
• The jobs are launched as foreground tasks by default - they will block the terminal until they are done.
• To launch a job in the background, use the symbol & at the end of the command line.
• A job can be temporarily suspended with Ctrl-z or terminated with Ctrl-c.
• A job can be intentionally sent to the background with the command bg or brought to the foreground with the command fg.