tcsh

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TENEX C Shell
Tcsh screenshot.png
Screenshot of a sample tcsh session
Developer(s) Ken Greer, Paul Placeway, Christos Zoulas, et al.
Stable release 6.18.01 / February 13, 2012 (2012-02-13)
Written in C
Operating system Cross-platform
Type Unix shell
License BSD License
Website http://www.tcsh.org/

tcsh (/ˌtˈsʃɛl/ "tee-cee-shell", /ˈtʃɛl/ "tee-shell", or as an acronym "tee cee ess aitch") is a Unix shell based on and compatible with the C shell (csh). It is essentially the C shell with programmable command line completion, command-line editing, and a few other features.

History[edit]

The “t” in tcsh comes from the “T” in TENEX, an operating system which inspired Ken Greer at Carnegie Mellon University, the author of tcsh, with its command-completion feature.[1] Greer began working on his code to implement Tenex-style file name completion in September 1975, finally merging it into the C shell in December 1981.[2] Mike Ellis at Fairchild A.I. Labs added command completion in September 1983.[2] On October 3, 1983, Greer posted source to the net.sources newsgroup.[2]

Paul Placeway from Ohio State University continued work on it in the 1980s, and since then it has been maintained by numerous people. Wilfredo Sanchez, the former lead engineer of Mac OS X, worked on tcsh in the early 1990s at MIT.

Significant features[edit]

  • Command history
    • The built-in history command displays the previously-entered commands
    • Use of / at the command line to allow the user to select a command from the history to edit/execute
    • Invoking previous commands using command history
      • !! executes the previous command
      • !n executes the nth command that was previously executed
      • !-n executes the command that was executed n commands ago
      • !string executes the most recently executed command that starts with string
      • !?string executes the most recently executed command that contains string
    • Using history in new commands
      • !* - refers to all of the arguments from the previous command
      • !$ - refers to the last argument from the previous command
      • !^ - refers to the first argument from the previous command
      • !:n - refers to the nth argument from the previous command
      • !:m-n - refers to the mth through nth arguments from the previous command
      • !:n-$ - refers to the nth through the last argument from the previous command
  • Command line editing
  • Auto-completion of file names and variables at the command line
  • Alias argument selectors; the ability to define an alias to take arguments supplied to it and apply them to the commands that it refers to. Tcsh is the only shell that provides this feature.
    • \!# - argument selector for all arguments, including the alias/command itself; arguments need not be supplied.
    • \!* - argument selector for all arguments, excluding the alias/command; arguments need not be supplied.
    • \!$ - argument selector for the last argument; argument need not be supplied, but if none is supplied, the alias name is considered to be the last argument.
    • \!^ - argument selector for first argument; argument MUST be supplied.
    • \!:n - argument selector for the nth argument; argument MUST be supplied; n=0 refers to the alias/command name.
    • \!:m-n - argument selector for the arguments from the mth to the nth; arguments MUST be supplied.
    • \!:n-$ - argument selector for the arguments from the nth to the last; at least argument n MUST be supplied.
#Alias the cd command so that when you change directories, the contents are immediately displayed.
alias cd 'cd \!* && ls'
  • Wildcard matching
if ( "$input" =~ [0-9]* ) then
  echo "the input starts with an integer"
else
  echo "the input does NOT start with an integer"
endif
  • Job control
  • The built-in where command. Works like the which command but shows all locations of the target command in the directories specified in $PATH rather than only the one that will be used.

Deployment[edit]

Early versions of Mac OS X shipped with tcsh as the default shell, but the default for new accounts is bash as of 10.3. (tcsh is still provided, and upgrading the OS does not change the shell of any existing accounts). The tcsh is the default root shell of FreeBSD (the default user shell is POSIX-based)[3] and its descendants like DragonFly BSD and DesktopBSD.

See also[edit]

References[edit]

  1. ^ "The T in tcsh". Archived from the original on 14 April 2012. Retrieved 31 October 2013. 
  2. ^ a b c Ken Greer (Oct 3 1983). "C shell with command and filename recognition/completion". net.sources. Web link. Retrieved Dec 29 2010.
  3. ^ Michael Urban; Brian Tiemann (2002). Sams teach yourself FreeBSD in 24 hours. Sams Publishing. p. 56. ISBN 978-0-672-32424-6. 

External links[edit]