Shell Programming

Examples of simple shell scripts:

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

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

Examples of  Bourne Shell Scripts

The examples are available at:

/home/cs476/public_html/shells

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: get the last string s_n of a file path name / s₁ / s₂ / ... / s_n /

#! /bin/sh

IFS=/

set $1

eval filename=$`echo $#`

echo $filename

mantopdfs: simple version of mantopdf 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

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 -s "ex1" $addr < $letter
 echo Mailed $letter to $addr
 index=`expr $index + 1`
done

Examples:

% ex1 ex1 wahab cs476

Will mail ex1 to both wahab and cs476.

% ex1 ex1 `cat list`

Will mail ex1 to each person listed on ‘list’.

ex1 : (csh)

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

#! /bin/csh
echo ‘Usage : ex1 letter u1 u2 .. //send letter to u1 u2 ..’
set letter=$1
set total=$#argv
set index=2
while ($index <= $total)
 Mail –s "ex1"   $argv[$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 user login//’
 
until who | grep $1 
do
 sleep 3
done
 

Example:

% ex2 wahab

Will return if wahab is login.

ex3 :

This programs gives a list of users currently login,

sorted by their login time.

#! /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 $3 $4 $1 >> /tmp/t$$ /* $3 day $4 time $1 user*/ 
 else
 sort /tmp/t$$
 rm /tmp/t$$
 exit
 fi
done

ex4 :

This program prints the number of files under a subtree.

The only argument is the root of the subtree.

#! /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$$ 
rm /tmp/t$$ 
 

Example:

% ex4 /home/cs476

ex5 :

This program creates a backup directory for c program’s 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
 

Example:

% cd ~/public_html/shells/BourneShell/testex5

% ../ex5

Ex6 :

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: ex6 [path] //scan . or [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

Example:

% cd ~/public_html/shells/BourneShell/testex6

% ../ex6 .

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C Shell versions of the above examples

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