Chapter 9: The TC Shell Everything you thought you knew is now wrong

In this chapter … Background Accessing tcsh Startup Files Commonality with bash Standard error Variables Control structures and builtins

Background TC Shell - an expansion of the C Shell from BSD The ‘T’ comes from TENEX and TOPS-20 OSes Meant to add features such as command completion to csh Not a very good scripting language – bash is much better Most features in bash are in tcsh, just might have different syntax

Shell Scripting Caveat Recall that we can specify which shell to use for a script by starting the first line with #!/path_to_shell Without this line, tcsh will use sh to execute the script unless you run the script with tcsh explicitly Different than bash and other shells Even tcsh admits it’s not great

Accessing tcsh Easiest way is to just issue tcsh Want to change your login shell to tcsh? –chsh Exiting tcsh –exit –logout (only if login shell) –CTRL-D (if ignoreeof not set)

Startup Files Logon shell –/etc/csh.cshrc –/etc/csh.logon –~/.tcshrc or ~/.cshrc –~/.login Non-logon shell –/etc/csh.cshrc –~/.tcshrc or ~/.cshrc

More files On logout –/etc/csh.logout –~/.logout History events loaded from –~/.history

Things in common with bash Command line expansion –Called substitution in tcsh docs History –history builtin works the same –! history references work the same –Instead of HISTSIZE and HISTFILESIZE, tcsh uses history and savehist –If variable histlit is set, history shows literal commands before command line substitution

tcsh vs. bash con’t Aliases –Syntax: alias name “value” –Allows you to reference command line arguments using \!* or \!:n –Special aliases beepcmd – instead of bell cwdcmd – whenever you change directories periodic – a periodic command to run ( tperiod ) precmd – runs just before shell prompt shell – absolute path to use for scripts w/o #!

tcsh vs. bash con’t Job control –Almost identical, slightly different for multiple processes spawned at once Filename substitution –*, ?, [], {}, ~ all the same –~+, ~- not available Directory stack – same Command Substitution $() – NOT available –Use `command` instead

Standard Error tcsh doesn’t have an easy way to capture standard error like bash (i.e. 2> ) Instead we have to use >& to combine standard error and standard out So grab standard out first, then combine out and error to capture error Ex: (cat x y > results) >& errors

Word Completion Tab completion is similar in tcsh Start with an ambiguous reference then hit tab If there are multiple matches, it will maximize the length of the prefix Will *not* show a list of possible matches unless you press CTRL-D

Variables In tcsh, there are two scopes, local and global To declare a local variable, use: set variable = value –Note the spaces – different than bash To declare a local integer variable = value To declare a global (avail. to child procs): setenv variable value

Variables con’t Just like bash, use a $ to reference a variable’s contents (also ${ } ) unset, unsetenv removes variables To declare an array of strings: set variable = ( values … ) To reference single entries use [] operator (base 1) echo variable[2] set variable[4] = “Value”

Numeric Variables builtin lets you work with numeric expressions variable = ( $count + 4 ) / 5 Caveat – separate each element by a space Available operators: =, +=, -=, *=, /=, %=, +, -, *, /, %

Numeric Variables con’t To make an array of numeric variables, you actually have to use set set variable = ( ) Then to access the variable[2] = 2

More variable goodness $#variable – displays the number of elements in a variable array $?variable – displays whether the variable is set (1 for set, 0 for not set) To read user input into a variable, set the variable to “$<“ –E.g. in a script echo –n “Enter a value:” set usr_input = “$<“

Important Shell Variables autologout – set timeout period cwd – contains current working directory histfile – contains location of history history – how many history items to keep home – your home directory mail – where your mail is stored owd – previous (old) working directory

Shell Variables, con’t histlit – show literal commands in history ignoreeof – ignore CTRL-D nobeep – disables shell beeps noglob – turns of file globbing rmstar – prompt for rm * commands visiblebell – causes screen to flash for bells

Shell Variables, con’t argv – array of command line args –$n, $* –Use $#argv to get number of args

Misc bindkey Control structures