This line reads: If the number of arguments ($#argv) passed in from the command line is not equal to one, then…

If the first line is true, this line and line 3 are executed.

The program exits with a value of one, meaning it failed.

Every if block is closed with an endif statement.

The user is asked for input. If the user just presses Enter, the variable name is set, but it is set to null.

The variable is quoted (double quotes) so that if the user enters more than one word in name, the expression will still be evaluated. If the quotes were removed and the user entered first and last name, the shell would exit the script with the error message if: Expression syntax. The empty double quotes represent a null string.

This line reads: If the value of $answer matches a Y or a y , followed by zero or more characters, then go to line 2; otherwise, go to line 3. (The * is a shell metacharacter.)

The user bob is mailed the contents of the file datafile.

The commands under the else are executed if line 1 is not true.

The user john is mailed the contents of the file datafile.

The endif block ends the if block.

The logical expression is being evaluated. The first expression is enclosed in parentheses (not necessary because && is of higher precedence than ||). The parentheses do not require spaces when nested, but the negation operator (!) must have a space after it.

If the expression evaluates true, this line is executed.

The tcsh program is executed with the -x switch. This turns on echoing. Every line in your script is echoed back to you after variable substitution has been performed.

If grade is less than 0 OR grade is greater than 100, the user has entered an illegal grade. Note the OR here. Only one of the expressions must evaluate to true for the whose expression to be true.

If grade is greater than or equal to 90 AND grade is less than or equal to 100, then echo "You got an A!" Both expressions surrounding the && must be true or program control will go to the else if on line 2.

If line 1 is false, test the expression (line 2), and if it is true, echo "You got a B."

If line 1 and 2 are both false, try this one. If this expression is true, then echo "You're average."

If all of the above expressions test false, the statements in the else block are executed.

The endif ends the entire if construct.

The grep program found ellie in the /etc/passwd file.

The grep program, if it finds the pattern ellie, returns a zero status when it exits.

The grep program did not find joe in the /etc/passwd file.

The grep program returns a nonzero status if the pattern is not found.

If the number of arguments passed in from the command line ($#argv) is not equal to one, then go to line 2.

The echo prints the script name ($0) and the string "requires an argument".

The program exits back to the prompt with a value of 2. This value will be stored in the status variable of the parent shell.

The end of the conditional if.

At the command line, the program checkon is executed without an argument.

The program exits with a value of 2, which is stored in the status variable.

The ypmatch program checks the NIS database to see if the name of the user, passed in as the first argument, is in the database.

If the status returned from the last command is zero, the then block is executed.

This line is executed if the if test expression evaluated to be true.

The who command is piped to the grep command. All of the output is sent to /dev/null, the Linux "bit bucket." The output of the who command is sent to grep; grep searches for the name of the user stored in the $1 variable (first command line argument). If grep is successful and finds the user, an exit status of zero is returned. The shell will then invert the exit status of the grep command to yield one, or true. If the shell evaluates the expression to be true, it executes the commands between the then and endif.

If the TC shell evaluates the expression in line 1 to be true, lines 2 and 3 are executed.

All the processes running and owned by $1 are displayed.

The endif ends the if statements.

The ypmatch command is used to search the NIS passwd file, if you are using a network. If the command succeeds in finding the user ($user) in the passwd file, the expression evaluates to be true. The exclamation point (!) preceding the expression nots or complements the expression; that is, makes it false if it is true, and vice versa.

If the expression is not true, the user is not found and this line is executed.

The endif ends this if block.

The label is a user-defined word with a colon appended. The label is called start-over. During execution of the program, the label is ignored by the shell, unless the shell is explicitly directed to go to the label.

The user is asked for input.

If the expression is true, (the user entered a grade less than 0 or greater than 100), the string " Illegal grade " is printed, and the goto starts execution at the named label, startover. The program continues to execute from that point.

The if expression tested false, so this line is printed.

The goto sends control to line 1 and execution starts after the label, startover.

The statement reads, if the file exists, then…

The statement reads, if the file is a directory, then…

The statement reads, if the file is not of zero length, then…

The statement reads, if the file is readable and writeable, then… A single option precedes the filename (e.g.,-r file && -w file && -x file).

The file testing flags can be stacked, as in -rwx file (new with tcsh).

The foreach loop iterates through the list of files produced by the Linux ls program, one file at a file, assigning each filename to the variable file.

If the file is readable, writable, and a plain file (-rwf), line number 3 is executed. The stacking of these file testing options is legal in tcsh, but not in csh.

This line is executed if the filename being tested is readable, writable, and executable.

Each of the files, dirstack, file.c, and xxx, are tested to see if they are readable, writable, plain files. For the first two files the test returns true (1 1), and for the last the test returns false (0).

The filetest command returns 1 if the file, hdd, is a block special device file. It is. Otherwise, 0 is returned.

The filetest command returns 1 if the file, fd, is a symbolic link and is readable and executable. It is. Otherwise, 0 is returned.

Today's date is printed.

With the -A option, the filetest built-in prints the date (in epoch form) when myfile was last accessed.

With the -A: option, the filetest built-in prints the date in timestamp format.

With the -U option, the filetest built-in prints the numeric user id for the owner of myfile.

With the -P: option, the filetest built-in prints the octal permission mode with a leading 0. Without the colon, the leading zero is removed.

This is an alias called Usage that can be used to produce an error message and exit the program.

This is an alias called Error that will produce an error message followed by any arguments passed when called.

The variable file is set to the first argument passed in from the command line, $1.

If the number of arguments passed is 0, i.e., no arguments were provided, the alias Usage will print its message to the screen.

If file (after variable substitution) is a file that does not exist (note the not operator, !), the alias, Error, under the then keyword displays its message.

If the file is a directory, print " testing is a directory. "

If the file is not a directory, else if the file is a plain file, then … the next statement is executed, another if.

This if is nested in the previous if. If file is readable and executable, then… This if has its own endif and is lined up to indicate where it belongs.

The endifterminates the innermost if construct.

The endif terminates the outermost if construct.

The user is asked for input.

The input is assigned to the color variable.

The switch statement evaluates the variable. The variable is enclosed in double quotes in case the user entered more than one word. The switch statement evaluates a single word or string of words if the string of words is held together with double quotes.

The case label is bl*, meaning that the switch expression will be matched against any set of characters starting with b, followed by an l. If the user entered blue, black, blah, blast, and so forth, the commands under this case label would be executed.

The breaksw transfers program control to the endsw statement.

If the switch statement matches this label, red, the program starts executing statements until the breaksw on line 9 is reached. Line 8 will be executed. "The sun is sometimes red" is displayed.

If line 4 is not matched, cases red and yellow are tested.

If either label, red or yellow, is matched, this line is executed.

The breaksw transfers program control to the endsw statement.

The default label is reached if none of the case labels matches the switch expression. This is like the if/else if/else construct.

This line is printed if the user enters something not matched in any of the above cases.

This breaksw is optional because the switch will end here. It is recommended to leave the breaksw here so that if more cases are added later, it will not be overlooked.

The endsw terminates the switch statement.

The variable release is assigned the output of uname -r, the release number for the version of the operating system.

The switch command evaluates the output of uname -s, the name of the operating system.

If the system type is SunOS, the case command on line 3 is executed.

The value of the variable release is evaluated in each of the cases for a match.

The case for all release versions 4 are tested.

The case for all release versions 5 through 8 are tested.

The inner switch statement is terminated.

The outer switch statement is terminated.

The user is asked to select from the menu.

The here document starts here. EOF is a user-defined word terminator. Until EOF is found on a line by itself (against the left-hand margin), the text after the first EOF will be sent as a quoted block to the cat program. The cat program will send the text to standard output, the user's terminal.

This EOF terminates the here document.

The user types his choice from the menu items displayed; i.e., 1, 2, 3, or 4.

The switch statement is used to evaluate the choice.