Shell Programming

Examples of simple shell scripts: (/home/cs476/shells/BourneShell/)

man2pdf : converts a man page to pdf

#! /bin/sh

troff -man  /usr/share/man/man1/$1.1 > t2

cat t2 | dpost > t3

ps2pdf t3  $1.pdf

man2pdfs : simple version of man2pdf

#! /bin/sh

 
 
troff -man /usr/share/man/man1/$1.1 | dpost | ps2pdf - $1.pdf 
 

Note that man2pdfs does not use temporary files.

(thus you do not have to worry about permissions to create such files and deleting them at the end)

Introduction to Bourne Shell

for more details see man page for sh (% man sh) (sh.pdf).

Loop Statements:

while list until list      for name [ in word ... ]
do do do

list list                 list

done done  done

Example: forexample

for i

do

echo $i

done

% forexample 1 2 a b

1

2

a

b

Conditional Statements:

if  list              case word in
then pattern)     list ;;
      list                  pattern)     list ;;
[ elif list                     .........
then   esac
       list  ] ...
[ else
       list  ]
fi

Misc. Statements:

test: Evaluates conditional expressions

example:    test $i -le 2
returns 0 (true) if $i is less than or equal to 2.

expr: Evaluates arithmetic expression

example: i=`expr $i + 1`
increments i by 1 (like i++ in C).

read: Reads one line from standard input

read var
   reads a line from stdin and assign it to var

example: readexample

while read line

do

echo $line

done

% readexample < readexample

echo: Writes to the standard output

example:  echo  "the line read is:"   $var
   writes:  the line read is: <the content of  var>

set: Assigns values to positional parameters $1, $2, ...

example:  set hello world
                   echo $2 

world (the value is of $2 is: world)

IFS: Internal Field Separators

example:  IFS=@
                      set hello@world
                      echo $2  

world (the value is of $2 is: world)

eval: Executes a command

example: cmd="ls -l"
eval $cmd

Examples of  Bourne Shell Scripts

The examples are available at: /home/cs476/public_html/shell/BourneShell

ê man-to-pdf: converts a man page to pdf

if test $# -eq 0

then

echo "usage man-to-pdf <cmd>"

echo "e.g., man-to-pdf touch"

exit

fi

if whereis $1 | grep man > /dev/null

then

filepath=` whereis $1 | tr ' ' '\n' | grep man | head -1 `

filename=` basename $filepath`

else

echo "man page for $1 is not found"

exit

fi

troff -man $filepath > /tmp/t1$$

echo ..done troff

cat /tmp/t1$$ | dpost > /tmp/t2$$

echo ..done dpost

ps2pdf /tmp/t2$$ $HOME/$filename.pdf

echo ..done ps2pdf

echo "the pdf file is:"

ls -lt $HOME/$filename.pdf

rm /tmp/t1$$ /tmp/t2$$

echo DONE

Ø man-to-pdfs: simple version of man-to-pdf that does not use tmp files:

troff -man $filepath | dpost | ps2pdf - $HOME/$filename.pdf

Replaces:

troff -man $filepath > /tmp/t1$$

cat /tmp/t1$$ | dpost > /tmp/t2$$

ps2pdf /tmp/t2$$ $HOME/$filename.pdf

ê mail-to-group :

This program mails a file to a group of users.

The first attribute is the file name, followed by the recipients’ email.

echo ‘Usage : mail-to-group letter u1 u2 ....//send letter to users u1 u2 ..’
 
letter=$1
shift
for i 
do
 Mail -s "shell example" $i < $letter
 echo Mailed $letter to $i
done

Examples:

% mail-to-group mail-to-group wahab cs476

Will mail the “mail-to-group” file to both wahab and cs476.

% mail-to-group mail-to-group `cat list`

Will mail the file to each person listed on ‘list’.

Ø mail-to-group-csh : (csh version )

This is the same as the previous example but uses csh instead of Bourne shell.

#! /bin/csh
set letter=$1
set total=$#argv
set index=2
while ($index <= $total)
 Mail –s "shell example" $argv[$index] < $letter
 echo mailed $letter to $argv[$index]
 @ index++
end
 

ê when-login :

This program informs you when a specific user login to a machine.

It has one argument, the user to watch for.

 
until who | grep $1 
do
 sleep 3
done
 

Example:

% when-login wahab

Will return if wahab is login.

ê who-login:

This programs gives a list of users currently login, sorted by their login time.

#! /bin/sh
echo ‘Usage: who-login’




who | sortout 
 

sortout

#! /bin/sh
while :
do
 if read line
 then
set `echo $line`
echo $3 $4 $1 >> /tmp/t$$ /* $3 day $4 time $1 user*/ 
 else
 sort /tmp/t$$
 rm /tmp/t$$
 exit
 fi
done

ê count-files :

This program counts the number of files under a subtree.

The only argument is the root of the subtree.

echo ‘Usage: count-files <path>’
 
touch /tmp/t$$
find $1 -type f -exec /usr/bin/echo "1\c" >> /tmp/t$$ \;
wc -c < /tmp/t$$ 
rm /tmp/t$$ 
 

Example:

% count-files /home/cs476

ê scan-dir :

This program recursively scans a directory

and prompts the users for a command to execute on each file under the directory.

#! /bin/sh
echo ‘Usage: scan-dir [path]’ 
 
case $# in
 0) dir=. ;;
 1) dir=$1 ;;
esac
echo .... scanning directory $dir




cd $dir




for i in *
do
  if test -d $dir/$i
  then
  $0 $dir/$i
  else
  ls -l $i
  echo -n type any command: 
  read command
  eval $command
  fi
done

Example:

% ../scan-dir /home/cs476/public_html/shells/BourneShell/test-scan-dir