Lecture 4Lecture 4

C Shell Scripts(Chapter 10)C Shell Scripts(Chapter 10)

Shell script/programShell script/program

Shell script: a series of shell commands Shell script: a series of shell commands placed in an ASCII text fileplaced in an ASCII text file

Commands includeCommands include Anything you can type on the command lineAnything you can type on the command line Variables (including shell vars, env vars, Variables (including shell vars, env vars,

command args…) and Expressionscommand args…) and Expressions Control statements (if, while, for)Control statements (if, while, for)

Script executionScript execution

Two ways to run a shell script:Two ways to run a shell script: Launch a subshell with the script name as the Launch a subshell with the script name as the

argument. e.g. % cshargument. e.g. % csh my_script.sh my_script.sh Specify which shell to use within the scriptSpecify which shell to use within the script

• First line of script is as First line of script is as #!/usr/bin/csh#!/usr/bin/csh #!/usr/bin/csh –f to not read in .cshrc#!/usr/bin/csh –f to not read in .cshrc

• Make the script executable using Make the script executable using chmodchmod• Make sure the PATH includes the current directoryMake sure the PATH includes the current directory• Run directly from the command lineRun directly from the command line

Shell Script ExampleShell Script Example

file ./hello.sh:file ./hello.sh:

#!/usr/bin/csh -f#!/usr/bin/csh -f

echo Hello Worldecho Hello World

% chmod +x ./hello.sh% chmod +x ./hello.sh

% ./hello.sh% ./hello.sh

ExpressionsExpressions

C Shell expressions are used with @ or with C Shell expressions are used with @ or with (if/while) statements, where variable can be(if/while) statements, where variable can be

Expression are formed by variables + operatorsExpression are formed by variables + operators @ operator: assigns the value of arithmetic @ operator: assigns the value of arithmetic

expressions to a variableexpressions to a variable Example of @:Example of @:

% set n=2% set n=2% @ a=$n + 2% @ a=$n + 2% @ a* = 2% @ a* = 2

Spaces must surround operators!Spaces must surround operators!

OperatorsOperators Arithmetic operatorsArithmetic operators Assignment Operators ( =, +=, -=…)Assignment Operators ( =, +=, -=…) Comparison Operators (==, !=, <=…)Comparison Operators (==, !=, <=…) Bitwise and logic operators (!, &&, ||), (>>, <<)Bitwise and logic operators (!, &&, ||), (>>, <<) Pattern matching (=~, !~)Pattern matching (=~, !~)

File test operators (operator + File test operators (operator + filename)filename)

-d file: the file is a dir?-d file: the file is a dir? -e file: the file exists?-e file: the file exists? -f file: the file is a plain file?-f file: the file is a plain file? -o file: the user owns the file-o file: the user owns the file -r/w/x file: the user has read/write/execute -r/w/x file: the user has read/write/execute

permissionpermission -z file: the file has 0 size-z file: the file has 0 size ! + any above: reverse the meaning! + any above: reverse the meaning

Control StatementsControl Statements if… then…[else…]endifif… then…[else…]endifif (if (condition)condition)thenthenstatementsstatements

elseelsestatementsstatements

endifendif While…endWhile…end

Syntax:Syntax:while (while (condition)condition)statementsstatements

endend foreach...endforeach...endforeach foreach varvar ( (list)list)

statementsstatementsendend

Parameter Passing Review

Positional Parameters $0 – the currently executing script $n – the nth parameter $# -- the number of parameters

Argument Array $argv[n] – the nth parameter (n > 0) $#argv – the size of argv

Example 1Example 1

Task: Write a script that lists all its Task: Write a script that lists all its command line arguments prepended by command line arguments prepended by arguments positional indexarguments positional index

Ex:Ex:% arg.csh a1 a2 % arg.csh a1 a2

the output after running the script is: the output after running the script is:

arg1 is a1arg1 is a1

arg2 is a2arg2 is a2

Script: arg_v1.cshScript: arg_v1.csh

#!/usr/bin/csh –f#!/usr/bin/csh –fset n = 1set n = 1 #positional index #positional indexwhile ( $n <= $#argv )while ( $n <= $#argv )

echo “Arg $n is $argv[$n]”echo “Arg $n is $argv[$n]”#increment the value of n#increment the value of n@ n++ @ n++

endend==================================Notes:Notes: # for comments# for comments After @ a space is requiredAfter @ a space is required Other ways to do it?Other ways to do it?

Script: arg_v2.cshScript: arg_v2.csh

#!/usr/bin/csh –f#!/usr/bin/csh –f

set n = 1set n = 1 #positional index #positional index

while ( $#argv > 0)while ( $#argv > 0)

echo “Arg $n is $1”echo “Arg $n is $1”

shiftshift

@ n++ @ n++

endend

Example 2

Changing the access rights of the files in a directory recursively

It is simple but is very useful

Simple Solution

#!/bin/csh -f

foreach file (`ls`)

if ( -d $file ) thenchmod –R 750 $file else chmod 750 $fileendif

end

A Solution Using Arguments

#!/bin/csh -f

if ($#argv == 0) thenecho "Please give a permission"exit 1endif

foreach file (`ls`)

if ( -d $file ) thenchmod -R $1 $file else chmod $1 $fileendif

end

A Solution Using while loop#!/bin/csh -fif ($#argv == 0) thenecho "Please give a permission"exit 1endif set file_set = `ls`set n = 1while($n <= $#file_set)set file = $file_set[$n]echo "The name of file is : $file ."if ( -d $file ) thenchmod -R $1 $fileelse chmod $1 $fileendif@ n ++end

Another Solution#!/bin/csh -fif ($#argv == 0) thenecho "Please give a permission"exit 1endif set files_set = `ls`foreach file (files_set)if ( -d $file ) thenchmod -R $1 $file else chmod $1 $fileendifend

Doesn’t Work!!

A Corrected Solution #!/bin/csh -f if ($#argv == 0) then echo "Please give a permission" exit 1 endif set files_set = `ls` foreach file ($files_set[*]) if ( -d $file ) then chmod -R $1 $file else chmod $1 $file endif end

Example 3Example 3 Task: Write a script that prints similar info. as ls Task: Write a script that prints similar info. as ls

–l, but in more user-friendly way.–l, but in more user-friendly way. Ex: Ex:

% fileinfo.csh bob (can take multiple args)% fileinfo.csh bob (can take multiple args)(Assume: ls –l bob => -rwsr-xr-x bill ….)(Assume: ls –l bob => -rwsr-xr-x bill ….)the output after running the script is:the output after running the script is:bob is a regular filebob is a regular fileyou own the fileyou own the fileyou have read permissionyou have read permissionyou have write permissionyou have write permissionyou have execute permissionyou have execute permission

Script: fileinfo.cshScript: fileinfo.csh#!/usr/bin/csh -f#!/usr/bin/csh -fset n = 1set n = 1

while ($n <= $#argv)while ($n <= $#argv) if(-d $argv[$n]) thenif(-d $argv[$n]) then echo "$argv[$n] is a directory"echo "$argv[$n] is a directory" endifendif if(-f $argv[$n]) thenif(-f $argv[$n]) then echo "$argv[$n] is a regular file"echo "$argv[$n] is a regular file" endifendif if(-o $argv[$n]) thenif(-o $argv[$n]) then echo "You own the file"echo "You own the file" elseelse echo "You do not own the file"echo "You do not own the file" endifendif

if(-r $argv[$n]) thenif(-r $argv[$n]) then echo "You have read permission"echo "You have read permission" endifendif

if(-w $argv[$n]) thenif(-w $argv[$n]) then echo "You have write permission"echo "You have write permission" endifendif

if(-x $argv[$n]) thenif(-x $argv[$n]) then echo "You have execute echo "You have execute

permission"permission" endifendif

@ n++@ n++endend

Example 4Example 4 Task: Write a script called average.csh that reads a list Task: Write a script called average.csh that reads a list

of integers on stdin and prints how many numbers were of integers on stdin and prints how many numbers were read, their sum and integer average.read, their sum and integer average.

Note: should handle the case there are not numbers read and Note: should handle the case there are not numbers read and not produce “division by 0” errornot produce “division by 0” error

Ex:Ex:% average.csh << .% average.csh << .> 10> 10> 20> 20> 30> 30> .> .3 numbers have been read3 numbers have been readthe sum is 60the sum is 60Integer average was 20Integer average was 20

Script : average.cshScript : average.csh#!/usr/bin/csh -f#!/usr/bin/csh -fset sum = 0set sum = 0set count = 0set count = 0set avg = 0set avg = 0

set num = $<set num = $<

while(($num !~ [a-z]*) && while(($num !~ [a-z]*) && ($num != ""))($num != ""))@ sum += $num@ sum += $num

@ count++@ count++ set num = $<set num = $<endend

echo "the total numbers are echo "the total numbers are $count"$count"

echo "the sum is $sum"echo "the sum is $sum"

if($count >0) thenif($count >0) then @ avg += $sum@ avg += $sum @ avg /= $count@ avg /= $count echo "Integer average is echo "Integer average is

$avg"$avg"elseelse echo "Integer average is echo "Integer average is

0"0"endifendif

Debugging C Shell ScriptDebugging C Shell Script C Shell has two command line options to help to C Shell has two command line options to help to

debug scripts by echoing each line of the script debug scripts by echoing each line of the script before actually executing it.before actually executing it. -v (verbose): echoes each line even before -v (verbose): echoes each line even before

performing variable substitutionperforming variable substitution -x: echoes each line after all substitution has been -x: echoes each line after all substitution has been

performed just before executing the actual commandsperformed just before executing the actual commands

How to use it:How to use it: % csh –xv script.csh% csh –xv script.csh #!/bin/csh –vx#!/bin/csh –vx

Or manually set echo points to avoid verbosityOr manually set echo points to avoid verbosity

Arguments to set

set echo Display each lines after variable substitution

and before execution set verbose

Display each line of script before execution, just as you typed it

Reading Assignment

Reading Chapter 10