Writing c shell scripts
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Writing C-shell scripts. #!/bin/csh # Author: Ken Berman # Date: 8-8-2002 # Purpose: display command and parameters echo $0 echo $argv[*]. Commands and Expressions. Commands: Sequence of UNIX commands, separated by ';' or on different lines Typically returns value via stdout

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Writing C-shell scripts

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Writing C-shell scripts

#!/bin/csh

# Author: Ken Berman

# Date: 8-8-2002

# Purpose: display command and parameters

echo $0

echo $argv[*]


Commands and Expressions

  • Commands:

    • Sequence of UNIX commands, separated by ';' or on different lines

    • Typically returns value via stdout

  • Expression

    • Logical expression similar to C language

    • Returns Boolean value (or integer)


Control structures for csh

if (expression)simple command

if (expression) then

commands

endif

if (expression) then

commands

else

commands

endif


Control structures continued

switch(testcase)

casepattern1:

commands

breaksw

casepattern2:

commands

breaksw

default:

commands

endsw


Control structures continued

while (expression)

commands

end

foreachvar(wordlist)

commands

End


Variables

  • String variables set name = value

  • Integer variables @ name = value


Examples of variables

% set name = Fred

% echo name

name

% echo $name

Fred

% set name #not the same as

% unset name

% set colors = ( red green blue)

% echo $colors[1]

red


Variables continued

% echo $colors

red green blue

% echo $colors[1-2]

red green

% echo $colors[4]

Subscript out of range


Parameters for calling a script

Parameters to a script are positional parameters $argv[1], $argv[2],… same as $1, $2,…

$#argv number of arguments

$argv[*] word list of all arguments

$0 name of command (i.e. filename of script)

$argv[0] is not defined


Different ways to display all parameters

#!/bin/csh

echo $argv[*]

while ( $#argv > 0 )

echo $argv[1]

shift

end


Display parameters in reverse order

set i = $#argv

while ( $i )

echo $argv[$i]

@ i--

end


Logical expressions

if ($#argv == 0) echo "No arguments given"

Logical expressions can be formed with

==equal!= not equal

=~ string match!~ string nonmatch

&&and

||or

!not

Expressions have to evaluate to an integer or simple string


Hints for hw3

  • Create a shell vector variable containing usernames from first column of who (can use awk to do this).

  • For each username use grep –c to count number of occurrences of username and apply sed to delete those usernames that occur less then n times.

  • Use if-else control structure to check whether there are two arguments and whether flag –t has been used

  • Use awk to output results in a table


Logical expressions involving files

-d filenamefile is a directory

-e "file exists

-f "file is an ordinary file

-o " user owns file

-r "user has read access

-w " user has write access

-x"user has execute access

-z"file is 0 bytes long

Example: if (-e $file && -f $file ) then …


Finds a given command on the search path. The pathname found or a failure message is displayed. Simulates the command "which"

#!/bin/csh

set cmd = $1

foreach dir($path)

if (-e $dir/$cmd) then

echo FOUND: $dir/$cmd

exit(0)

endif

end

echo $cmd NOT on $path


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