$?PATH is a test to see if the PATH variable has been set; it returns 1 if true.

If the PATH variable has been set, /usr/X11R6/bin is appended to it. This is a directory that contains the X windows files.

If the PATH variable has not been previously set, this line sets it to: /bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin

This line checks to see if the prompt has been set.

When you place the expression in square brackets, the expression will be tested and if the result of the expression is true, a zero exit status is returned; otherwise a nonzero exit status is returned. If the value of the SHELL environment variable is /bin/tcsh, the exit status will be 0.

The status variable contains the exit status of the last command executed, which in this example, is the previous test on line 5.

If the status from the last command was zero, the prompt for the /bin/tcsh is set. The prompt will be set to the user's name followed by an @ symbol, the hostname, and the current working directory (all enclosed in [ ]), followed by a dollar sign; e.g., [ ellie@homebound ~ ]$

If the status was nonzero, the else branches program control to line 9.

This line sets the prompt for the standard csh program. It will print the user's name (id -un), an @ symbol, and the short name for his host machine, i.e., the hostname cut at the first dot, and a $.

The endif terminates the inner if block.

The size of core files (usually created when a program crashes for some illegal system operation) is limited to 1000000 bytes. Core files are created if you abort a running program with Control-.

If the group id number and the user id number are the same, and the user id number is greater than 14, then the next line will be executed; otherwise, the line under the else will be executed. Typically, user ids below 14 are for special users, such as root, daemon, adm, lp, etc. (See /etc/passwd. The user id is in field number 3.)

If the test in the previous line returned a nonzero exit status, line 14 is executed, else line 15 is executed.

The umask sets the file creation mask; i.e., the initial permissions for files and directories when created. Directories will get 755 (rwxr-xr-x) and files will get 644 (rw-r--r--) when they are created.

Umask is set so that when a directory is created, its permissions will be 775 (rwxrwxr-x) and files will get 664 (rw-rw-r--).

The environment variable HOSTNAME is assigned the output of the /bin/hostname command.

The history variable is set to 1000. When commands are typed at the command line, they are saved in a history list. When you set the history variable to 1000, no more than 1000 commands will be displayed when the history command is typed.

The test command returns zero exit status if the /etc/profile.d directory exists, and nonzero if it doesn't.

If the status is 0, the directory exists, and the program branches to line 20.

Thenonomatch variable is set to prevent the shell from sending an error message if any of its special metacharacters (*, ?, []) cannot be matched.

The foreach loop assigns each file, with a .csh extension (*.csh) in the /etc/profile.d directory, to the variable i, in turn, looping until each file has been tested (lines 22–24).

If the filename assigned to variable i is a regular file (-f), then go to the next line.

If the test returned a 0 status (true), then source the file; i.e., execute it in the context of the current environment.

The end keyword marks the end of the loop body.

If the prompt has been set ($?prompt), the shell is running interactively; i.e., it is not running in a script. Prompts are set only for interactive shells.

The primary prompt is set to the number of the current history event, the name stardust, and a > character. This will change the > prompt, the default.

The history variable is set to 100. This controls the number of history events that will appear on the screen. The last 100 commands you entered will be displayed when you type history (See History.)

Normally, when you log out, the history list is cleared. The savehist variable allows you to save a specified number of commands from the end of the history list. In this example, the last five commands will be saved in a file in your home directory, the .history file, so that when you log in again, the shell can check to see if that file exists and put the history lines saved at the top of the new history list.

The noclobber variable is set to protect the user from inadvertently removing files when using redirection. For example, sort myfile > myfile will destroy myfile. With noclobber set, the message "file exists" will appear on the screen if you attempt to redirect output to an existing file.

If the tcsh variable, rmstar, is set, the user will be asked if he really wants to remove all his files after entering rm *; i.e., he is given a chance to save himself from removing all files in his current working directory.

The cdpath variable is assigned a list of path elements. When changing directories, if you specify just the directory name, and that directory is not a subdirectory directly below the current working directory, the shell will search the cdpath directory entries to see if it can find the directory in any of those locations and then will change the directory.

The ignoreeof variable prevents you from logging out with ^D (Control-D). Linux utilities that accept input from the keyboard, such as the mail program, are terminated by pressing ^D. Often, on a slow system, the user will be tempted to press ^D more than once. The first time, the mail program would be terminated; the second time, the user is logged out. By setting ignoreeof, you are required to type logout to log out.

The aliases are set to give a shorthand notation for a single command or group of commands. Now when you type the alias, the command(s) assigned to it will be executed. The alias for the more command is m. Every time you type m, the more command is executed. The status alias prints the date and a summary of the user's disk usage. The cd alias creates a new prompt every time the user changes directories. The new prompt will contain the number of the current history event (!*) and the current working directory ($cwd) surrounded by < >. (See Aliases.)

The endif marks the end of the block of statements following the if construct on line 1.

The stty command sets options for the terminal. Input characters will not be stripped to seven bits if -istrip is used.

The stty command sets Control-H, the Backspace key, to erase.

Any line beginning with # is a comment. It is not an executable statement.

If the current terminal window (tty) is the console (linux), the next line is executed; otherwise, program control goes to the last endif.

This line is echoed to the screen, and if the user does not press Control-C to kill the process, the program will sleep (pause) for five seconds, and then the X windows program will start.

The startx program launches X windows.

The endif marks the end of the innermost if construct.

The autologout variable is set to 60 so that after 60 minutes of inactivity, the user will automatically be logged out (from the login shell).

The search path is set for tcsh. It consists of a space separated list of directories searched from left to right by tcsh when a command is entered at the command line. The search path is local to the current shell. (See Setting Local Variables.)

The value of the path variable is displayed

The value of the environment variable, PATH, is displayed. It is a colon-separated list of the same directories as listed in the path variable, and is passed to other programs or applications invoked from the current shell. (Bash, sh, and ksh set the path as a colon-separated list.)

The primary prompt is assigned the user's login name (%n), followed by the hostname (%m), a space, and the current working directory. The string is enclosed in square brackets, followed by a #.

The new prompt is displayed. The ~ appearing in the prompt represents the user's home directory. The cd command changes directory to the parent directory.

The new prompt indicates the current working directory, /home. In this way the user always know what directory he is in.

This is an example of online scripting. Because the TC shell is expecting further input after the foreach loop is entered, the secondary prompt appears. The foreach loop processes each word in the parenthesized list.

The first time in the loop, joe is assigned to the variable pal. The user joe is sent the contents of memo in the mail. Then next time through the loop, tom is assigned to the variable pal, and so on.

The end statement marks the end of the loop. When all of the items in the parenthesized list have been processed, the loop ends and the primary prompt is displayed.

The primary prompt is displayed.

The secondary prompt, prompt2, is reset to the formatted string where %R is the name of the conditional or looping construct entered in line 2 at the primary prompt. The two percent signs will evaluate to one percent sign.

The foreach command has been started. This is a looping construct that must end with the keyword end. The secondary prompt will continue to appear until the loop is properly terminated.

The secondary prompt is foreach %.

After the end keyword is typed, the loop executes.

The primary prompt reappears awaiting user input.

The grep program searches for the pattern "ellie" in the /etc/passwd file and is successful. The line from /etc/passwd is displayed.

The status variable is set to the exit value of the grep command; 0 indicates success. The ? variable also holds the exit status. This is the variable used by the bash and ksh shells for checking exit status. (It is not used by csh.)

The grep program cannot find user nicky in the /etc/passwd file.

The grep program cannot find the pattern, so it returns an exit status of 1.

The grep fails because the file /etc/passsswd cannot be opened.

Grep cannot find the file, so it returns an exit status of 2.

The special tcsh variable printexitvalue is set. It will automatically print the exit value of any command that exits with a nonzero value.

The output of each of the commands is sent to the file called outputfile. Without the parentheses, the output of the first two commands would go to the screen, and only the output of the cal command would be redirected to the output file.

The pwd command displays the present working directory. The parentheses cause the commands enclosed within them to be processed by a subshell. The cd command is built-in to the shell. While in the subshell, the directory is changed to root and the present working directory is displayed. When out of the subshell, the present working directory of the original shell is displayed.

The output from the man pages for the tcsh program is piped to the printer. The ampersand at the end of the command line puts the job in the background.

There are two numbers that appear on the screen: the number in square brackets indicates that this is the first job to be placed in the background; the second number is the PID of this job.

The shell prompt appears immediately. While your program is running in the background, the shell is prompting you for another command in the foreground.