Variables

Variables Variables start with a $ sign when used. The variable gets no $ when declared. Declare a variable with the set command set X = "T" set X = $T set X = 1 set X = 1 + $# Or declare a variable (if it is a number) with the @ command (but you need a space after the “@”) @ X = $T @ X = 1 @ X = 1 + $# Undeclare a variable with the unset command unset X Only legal if $T is a number! 1

Array Variables • Use ( ) to declare an array • % set var2=(Apple Banana Cherry) • Use [ ] to access an array element • % echo $var2 • Apple Banana Cherry • % echo $var2[2] • Banana • Use - to access ranges • % echo $var2[2-3] • Banana Cherry • % echo $var2[-2] • Apple Banana 2

Array Variables • Use $#X to get the number of elements • % set var2=(Apple Banana Cherry) • % echo $#var2 • 3 • % echo $var2[2-$#var2] • Banana Cherry • Don’t use commas • % set var2=(Apple, Banana, Cherry) • % echo $var2[2] • Banana, • There is a built-in array, argv • There is not much difference between argv[2] and $2, or between $* and argv[*], or between $# and $#argv 3

Positional Parameters $0 : Name of the calling program $1 - $9 : Command-line Arguments The first argument is $1 The second argument is $2, etc. But $10 does not mean 10: % cat testscript echo "The word of the day is $10." % ./testcript at be cat do eat fee go hi it joy kit law The word of the day is at0. (2 digit arguments have to be shifted to use $1- $9)

shift shiftis used in C-shell if you want to access more than 9 parameters. Example: % cat demo_shift #!/bin/tcsh echo $1 $2 $3 shift echo $1 $2 shift echo $1 %. 5

shift shiftis used in C-shell if you want to access more than 9 parameters. Example: % cat demo_shift #!/bin/tcsh echo $1 $2 $3 shift echo $1 $2 shift echo $1 % ./demo_shift 1 2 3 1 2 3 2 3 3 % 6

The $< Special Parameter C shell is a programming language. So we should have a way to read keyboard input (just like other programming languages can). set X = $< or set X = "$<" $< is stdin But if you used “<” file redirection when running the script, then stdin can be a file. What about special symbols? set X = $<:q or set X = "$<" 7

New topic: reviewing C-shell syntax

foreach The foreach loop: foreach var ( arrayVariable OR wordlist ) command(s) end

foreach The foreach loop: #!/bin/tcsh foreach person (Bob Susan Joe) echo Hello $person end Output: Hello Bob Hello Susan Hello Joe

foreach • If you want to run a command once for each of a set of filenames, you can use a foreach loop foreach fn (file1 file2 file3 file4) cat $fn | wc end foreach fn (a*b) cat $fn | fgrep Hello | wc -l end set Z = ( A B C ) foreach fn ( $Z ) cat $fn | cut -c1 end

if Two forms: if ( <expression> ) <simple statement> And: if ( <expression> ) then <statements> else if ( <another-expression> ) then <statements> else <statements> endif Some of these spaces are necessary. csh is intensely picky about missing spaces. When in doubt: ADD SPACES! When you get an error message, try fixing it by: ADDING SPACES! 12

Conditional Expressions ! negate != not equal == equal >, <, <=, >= comparators, they work as you would expect =~ If the right hand side matches a pattern, (i.e., similar to filename matching, with asterisks and question marks.) !~ If the right hand side doesn't match a pattern, the condition is true.

Conditional File Tests Before moving on, there is a confusing hazard in C-shell conditional statements… Using the if command, filenames can be tested for the following: if ( -d filename ) # true if filename is a directory if ( -e filename ) # true if filename exists if ( -f filename ) # true if filename is a text file if ( -o filename ) # true if you own filename if ( -r filename ) # true if filename is readable if ( -w filename ) # true if filename is writable if ( -x filename ) # true if filename is executable if ( -z filename ) # true if filename is empty

Conditional Expressionsa tricky expression to test • Suppose you want to write a script that accepts a "-r" option, as an input argument. Well then, the following line will not work: if ( $argv[1] == -r ) echo "The -r flag was given." • If the first argument is "-r" then this is evaluated as: if ( -r =~ -r ) echo "The -r flag was given." • The C shell thinks you meant to use a file operator, and so it tests the file named "=~" to see if it is readable. Then it sees the next operator, which is again a "-r," but in this case there is no filename afterwards. This generates a syntax error. The solution is to place a dummy character before both strings: if ( X$argv[1] =~ X-r ) echo found it

Conditional Expressionsa tricky expression to test • Suppose you want to write a script that accepts a "-r" option, as an input argument. Well then, the following line will not work: if ($argv[1]==-r) echo "The -r flag was given." • If the first argument is "-r" then this is evaluated as: if ( -r == -r ) echo "The -r flag was given." • The C shell thinks you meant to use a file operator, and so it tests the file named "=~" to see if it is readable. Then it sees the next operator, which is again a "-r," but in this case there is no filename afterwards. This generates a syntax error. The solution is to place a dummy character before both strings: if ( X$argv[1] =~ X-r ) echo found it

Conditional Expressionsa tricky expression to test • Suppose you want to write a script that accepts a "-r" option, as an input argument. Well then, the following line will not work: if ($argv[1]==-r) echo "The -r flag was given." • If the first argument is "-r" then this is evaluated as: if ( -r== -r ) echo "The -r flag was given." • The C shell thinks you meant to use afile operator, and so it tests the file named "==" to see if it is readable. Then it sees the next operator, which is again a "-r," but in this case there is no filename afterwards. This generates a syntax error. The solution is to place a dummy character before both strings: if ( X$argv[1] =~ X-r ) echo found it Needless to say, your directory probably does not contain any file with such a weird name as ==. But, technically speaking, it is legal in UNIX to name a file with such a name.

Conditional Expressionsa tricky expression to test • Suppose you want to write a script that accepts a "-r" option, as an input argument. Well then, the following line will not work: if ($argv[1]==-r) echo "The -r flag was given." • If the first argument is "-r" then this is evaluated as: if ( -r==-r ) echo "The -r flag was given." • The C shell thinks you meant to use afile operator, and so it tests the file named "==" to see if it is readable. Then it sees the next operator, which is again a "-r," but in this case there is no filename afterwards.This generates a syntax error. The solution is to place a dummy character before both strings: if ( X$argv[1] =~ X-r ) echo found it

Conditional Expressionsa tricky expression to test • Suppose you want to write a script that accepts a "-r" option, as an input argument. Well then, the following line will not work: if ($argv[1]==-r) echo "The -r flag was given." • If the first argument is "-r" then this is evaluated as: if ( -r==-r ) echo "The -r flag was given." • The C shell thinks you meant to use afile operator, and so it tests the file named "=~" to see if it is readable. Then it sees the next operator, which is again a "-r," but in this case there is no filename afterwards. This generates a syntax error. The solution is to place a “dummy” character before both strings: if ( X$argv[1] == X-r ) echo "The -r flag was given." This time, if the first argument is “-r”, then the command evaluates as: if ( X-r == X-r ) echo "The -r flag was given" Consequently, the command now works, because, indeed, the X-r string does equal itself.

Conditional Expressionsa tricky expression to test • Suppose you want to write a script that recognizes whether the second command-line parameter begins with "-e”. It then prints that argument, but only if it begins with “-e”. • ./prog 1 2 3 4 • ./prog 1 –e 2 3 -e • ./prog 1 –exyz -exyz

Now, let’s work through an example, line by line…

Del Script #!/bin/csh foreach name ($argv) if ( -f $name ) then echo -n "delete the file '${name}' (y/n/q)?" else echo -n "delete the entire directory '${name}' (y/n/q)? " endif set ans = $< switch ($ans) case n: continue case q: exit case y: rm -r $name continue endsw end

Del Script #!/bin/csh foreach name ($argv) # $argv shell variable for an argument of a command if ( -f $name ) then echo -n "delete the file '${name}' (y/n/q)?" else echo -n "delete the entire directory '${name}' (y/n/q)? " endif set ans = $< switch ($ans) case n: continue case q: exit case y: rm -r $name continue endsw end

Del Script #!/bin/csh foreach name ($argv) if ( -f $name ) then #tests to see if the file whose name is in $name is an ordinary file, as opposed to a directory file. echo -n "delete the file '${name}' (y/n/q)?" else echo -n "delete the entire directory '${name}' (y/n/q)? " endif set ans = $< switch ($ans) case n: continue case q: exit case y: rm -r $name continue endsw end

Del Script #!/bin/csh foreach name ($argv) if ( -f $name ) then echo -n "delete the file '${name}' (y/n/q)?” #The echo -n prevents a skip to a new line;the -n option of echo tells the shell not to print the newline # character, so that our answer (“y”, “n”, or “q”), will be on the same line. else echo -n "delete the entire directory '${name}' (y/n/q)? " endif set ans = $< switch ($ans) case n: continue case q: exit case y: rm -r $name continue endsw end

Del Script #!/bin/csh foreach name ($argv) if ( -f $name ) then echo -n "delete the file '${name}' (y/n/q)?” else echo -n "delete the entire directory '${name}' (y/n/q)? " endif set ans = $< #the symbol $<means the input from the keyboard switch ($ans) case n: continue case q: exit case y: rm -r $name continue endsw end

Del Script #!/bin/csh foreach name ($argv) if ( -f $name ) then echo -n "delete the file '${name}' (y/n/q)?" else echo -n "delete the entire directory '${name}' (y/n/q)?" endif set ans = $< switch ($ans) #Control flow is switched to where the first match occurs case n: continue #go to the top of the enclosing loop case q: exit case y: rm -r $name continue endsw end

Del Script #!/bin/csh foreach name ($argv) if ( -f $name ) then echo -n "delete the file '${name}' (y/n/q)?" else echo -n "delete the entire directory '${name}' (y/n/q)?" endif set ans = $< switch ($ans) case n: continue case q: exit case y: rm -r $name #Actually removes the directory (because of -r) continue endsw end

Variables

Variables

Presentation Transcript

VARIABLES

VARIABLES

Physical Variables Social Variables Personality Variables Context Variables

Variables

Variables

Variables

Variables

Physical Variables Social Variables Personality Variables Context Variables

Variables

Variables

VARIABLES

Variables

Variables

VARIABLES

Variables

Variables

Variables

Variables

Variables