• Processes

  • ``An instance of an executing program.''

  • Each command processed by the shell (usually) spawns one or more processes.

  • Each process (usually) has at least three I/O streams associated with it: normal input (``stdin''), normal output (``stdout''), and error output (``stderr'').
    

  • Example:

    $ who am i $ ps -t ttyp1 $ ps axuw -t ttyp1

• I/O Redirection

  • A > sign in the command line redirects stdout to the file following.
    

  • A < sign in the command line redirects stdin to the file following.
    

  • You can also do both:
    

  • BAD Example:

    $ sort < file.dat > file.dat

    (destroys file.dat)

  • Better Example:

    $ sort -o file.dat < file.dat

    (file.dat opened for output by program, not shell)

• Pipes

  • A | (vertical bar) character between two shell commands sends the stdout of the first to the stdin of the second.
    

  • And you can string together an arbitrary number of them...
    

  • Unix programs can be (relatively) single-purpose and (therefore) simpler, free of ``features''.

  • Some examples:

    $ ls | wc -w $ ls -a | wc -w $ ls -als | sort -n $ du | sort -n | tail

  • Redirecting stderr:

    $ du ..|sort -n $ du ..|sort -n > du.out $ du .. 2> du.errs |sort -n > du.out $ du .. 2>&1 |sort -n > du.out

• Other Command Line Syntax

  • Command sequencing with ;

    $ finger pas ; ls -ld ~pas ; ps -u pas

  • Subshell execution with parens:

    $ (finger pas ; ls -ld ~pas ; ps -u pas) | less

  • Backtick substitution:

    $ cat ~pas/smoggies $ pine `cat ~/smoggies`

  • Advanced wildcards:

    • Character classes with [ ... ]

      $ lpr -P ansi *.[ch] $ vi file[0-3].dat

    • Alternatives with { ... }

      $ lpr -P postscript reports/{Jun,Jul,Aug}-2000/*.ps $ vi ed{bug,read,write}.c

  ---

• Job Control

  • control-Z stops a program

  • fg resumes (brings to foreground)

  • Example:

    $ vi .profile

  • Appending & to a command line runs the command in the background;

  • bg restarts a stopped job in the background. (Most useful with time-consuming non-interactive programs.)

  • jobs shows your current stopped/background jobs

  • Example:

    $ (echo "Job 1 start; sleep 60; echo "Job 1 done") & $ (echo "Job 2 start; sleep 60; echo "Job 2 done") & $ (echo "Job 3 start; sleep 60; echo "Job 3 done") & $ jobs

  ---

• Scheduled Jobs

  • Periodic Jobs with crontab

    $ crontab -e $ crontab -l

  • One-time Jobs with at

    $ at 11:23am echo "The date is" `date` ctrl-D $ at -l

  ---

• Aliases -- the simplest programs

  Examples:

  $ alias ll='ls -l' $ ll $ alias del='rm -i' $ alias pigs='ps axuw|sort +3 -n -r|head'

  ---

• Customization

  $ vi .profile

On to More Commands...