tcsh (// “tee-see-shell”, // “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.
Screenshot of a sample tcsh session
|Developer(s)||Ken Greer, Paul Placeway, Christos Zoulas, et al.|
tcsh added filename and command completion and command line editing concepts borrowed from the Tenex system, which is the source of the “t”. Because it only added functionality and did not change what was there, tcsh remained backward compatible with the original C shell. Though it started as a side branch from the original csh source tree that Bill Joy had created, tcsh is now the main branch for ongoing development. tcsh is very stable but new releases continue to appear roughly once a year, consisting mostly of minor bug fixes.
On many systems, such as Mac OS X and Red Hat Linux, csh is actually tcsh. Often one of the two files is either a hard link or a symbolic link to the other, so that either name refers to the same improved version of the C shell.
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. 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. Mike Ellis at Fairchild A.I. Labs added command completion in September 1983. On October 3, 1983, Greer posted source to the net.sources newsgroup.
- Command history
- The built-in
historycommand 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
!nexecutes the nth command that was previously executed
!-nexecutes the command that was executed n commands ago
!stringexecutes the most recently executed command that starts with string
!?stringexecutes 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
- The built-in
- 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.
\!$- argument selector for the last argument; argument need not be supplied, but if none is supplied, the alias name is considered to be the last argument.
\!^- argument selector for first argument; argument MUST be supplied.
\!:n- argument selector for the nth argument; argument MUST be supplied; n=0 refers to the alias/command name.
\!:m-n- argument selector for the arguments from the mth to the nth; arguments MUST be supplied.
\!:n-$- 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
wherecommand. Works like the
whichcommand but shows all locations of the target command in the directories specified in
$PATHrather than only the one that will be used.
Early versions of Mac OS X shipped with tcsh as the default shell, but the default for new accounts became 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) and its descendants like DragonFly BSD and DesktopBSD.
- Christos Zoulas. "tcsh-6.22.00 is now available!". mailman.astron.com. Retrieved 28 November 2019.
- Ken Greer (3 Oct 1983). "C shell with command and filename recognition/completion". Newsgroup: net.sources. Retrieved 29 December 2010.
- tcsh(1) man page. tcsh.
- Fixes file in tcsh-17 June 2000.
- Ubuntu - Details of package csh. Packages.ubuntu.com.
- Debian - Details of package csh. Packages.debian.org.
- Ubuntu - Details of package tcsh. Packages.ubuntu.com.
- Debian - Details of package tcsh. Packages.debian.org.
- "The T in tcsh". Archived from the original on 14 April 2012. Retrieved 31 October 2013.
- Michael Urban; Brian Tiemann (2002). Sams teach yourself FreeBSD in 24 hours. Sams Publishing. p. 56. ISBN 978-0-672-32424-6.
- POSIX 2008 Shell Command Language "The System V shell was selected as the starting point for the Shell and Utilities volume of POSIX.1-2008. The BSD C shell was excluded from consideration"