Shell Programming

Examples of simple shell scripts:

man2pdf : converts a man page to pdf

#! /bin/sh

ls -lt /usr/share/man/man1/$1.1

troff -man  /usr/share/man/man1/$1.1 > t2
echo ..done troff

cat t2 | dpost > t3
echo ..done dpost

ps2pdf t3  $1.pdf
echo ..done ps2pdf

man2pdfs : simple version of man2pdf

#! /bin/sh

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

NOTE: 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)

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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

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

example:   read var < file
reads a line from file and assign it to var

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

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Examples of  Bourne Shell Scripts

mantopdf: converts a man page to pdf

#! /bin/sh

if test $# -le 0

then

echo "usage mantopdf <file or cmd>"

echo "e.g., mantopdf touch"

echo "e.g., mantopdf pdftotext.1"

echo "e.g., mantopdf /usr/man/man1b/touch.1b"

exit

fi

if test -f $1

then

filepath=$1

else

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

if test -z "`echo $filepath`"

then

echo "man page for $1 is not found"

exit

fi

fi

filename=`path2file $filepath`

echo file path is:

ls -lt $filepath

echo file name is:

echo $filename

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

path2file:

#! /bin/sh

IFS=/

set $1

eval filename=$`echo $#`

echo $filename

mantopdfs: simple version of mantopdf

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

Ex1 : (sh)

This program mails a file to a group of users.

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

#! /bin/sh
echo ‘Usage : ex1 letter u1 u2 ....//send letter to users u1 u2 ..’
letter=$1
total=$#
index=2
while test $index -le $total
do
 eval addr=$`echo $index`
 Mail $addr < $letter
 echo Mailed $letter to $addr
 index=`expr $index + 1`
done

Ex1 : (csh)

This program mails a file to a group of users.

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

#! /bin/csh
echo ‘Usage : ex1 letter u1 u2 ....//send letter to users u1 u2 ..’
set letter=$1
set total=$#argv
set index=2
while ($index <= $total)
 mail $argv[$index] < $letter
 echo mailed $letter to $argv[$index]
 @ index++
end

Ex2 :

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

It has one argument, the user to wait for.

#! /bin/sh




 
 
echo ‘Usage: ex2 user // wait until <usr> login//’
 
until who | grep $1 
do
 sleep 3
done

Ex3 :

This programs gives a list of users currently logged on, sorted by their login time/user names

#! /bin/sh
 
Echo ‘Usage: ex3 //list who sorted by time of login//’




 
 
who > /tmp/f$$
 
sortout < /tmp/f$$ 
 
rm /tmp/f$$
 
 

sortout

#! /bin/sh




 
while :




 
 do
 if read line
 then
set `echo $line`
echo $5 $1 >> /tmp/t$$ /* $1 $5 to sort by user names */
 else
 sort /tmp/t$$
 rm /tmp/t$$
 exit
 fi
done

Ex4 :

This program prints the number of files in a subtree.

The only argument is the root of the tree to search in.

#! /bin/sh




 
echo ‘Usage: ex4 path //count files under path subtree//’




 
touch /tmp/t$$




 
find $1 -type f -exec /usr/bin/echo "1\c" >> /tmp/t$$ \;




 
wc -c < /tmp/t$$ 




 
rm /tmp/t$$ 

Ex5 :

This program creates a backup directory for C files

#! /bin/sh




 
echo ‘Usage: ex5 //copy c programs to $HOME/backup directory//’
 
if test ! -d $HOME/backup 
then
 echo $HOME/backup does not exist
 mkdir $HOME/backup
 echo ... $HOME/backup is created
fi
 
for i in *.c
do
 if test ! -f $HOME/backup/$i 




 
 then
  echo $i is not in $HOME/backup
  cp $i $HOME/backup/$i
  echo copied $i to $HOME/backup/$i




 
 else
  echo compring $i with $HOME/backup/$i
  if cmp -s $i $HOME/backup/$i
  then
   echo .... identical... 
  else
  echo .... different...
 echo copying $i to $HOME/backup/$i
  cp $i $HOME/backup/$i
  fi
 fi
done
 
 

Ex6 :

This program recursively scans the current directory

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

#! /bin/sh
echo ‘Usage: ex6 [<path>] //scan directory at <path> recursively//’ 
 
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

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Examples of  C Shell Scripts

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