tcsh

tcsh (/ˌtiːˈsiːʃɛl/ "tee-see-shell", /ˈtiːʃɛl/ "tee-shell", or as "tee see 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. Unlike the other common shells, functions cannot be defined in a tcsh script and the user must use aliases instead (as in csh). It is the native root shell for BSD-based systems such as FreeBSD.

History

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.^[2] 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.^[3] Mike Ellis at Fairchild A.I. Labs added command completion in September 1983.^[3] On October 3, 1983, Greer posted source to the net.sources newsgroup.^[3]

Significant features

• 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 n^th argument from the previous command
    • !:m-n - refers to the m^th through n^th arguments from the previous command
    • !:n-$ - refers to the n^th through the last argument from the previous command
• Command line editing
• Auto-completion of file names and variables as well as programmable completion 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 n^th argument; argument MUST be supplied; n=0 refers to the alias/command name.
  • \!:m-n - argument selector for the arguments from the m^th to the n^th; arguments MUST be supplied.
  • \!:n-$ - argument selector for the arguments from the n^th 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

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)^[4][5] and its descendants like DragonFly BSD and DesktopBSD.

See also

• Comparison of command shells

References

External links

• Official website
• tcsh manual page
• Archive for the O'Reilly book "Using csh and tcsh"