Shell Programming

Examples of simple shell scripts:

(/home/cs476/shells/BourneShell/) &

(/home/cs476/shells/BourneShell/linux)

Example1: 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

Example2: 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

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

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

expr: Evaluates arithmetic expression

e.g.: 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

e.g.: readexample

while read line

do

echo $line

done

% readexample < readexample

echo: Writes to the standard output

e.g.,: echo  "the line read is:" $line
writes:  the line read is: <the content of  var>

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

e.g.: set hello world
 echo $2

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

IFS: Internal Field Separators

e.g.: IFS=@
    set hello@world
    echo $2  

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

eval: Executes a command

e.g.: cmd="ls -l"
eval $cmd

Example 3: 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

Example 4: 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

Example 5: 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

E.g.:

% 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’.

Example 6: mail-to-group-csh (csh version )

This is the same as the previous example but uses csh.

 
#! /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
 

Example 7: 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
 

E.g.:

% when-login wahab

Will return if wahab is login.

Example 8: who-login

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

who | sortout 

sortout 

 
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

Example 9: 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$$ 
rm /tmp/t$$ 
 

E.g.:

% count-files /home/cs476

Example 10: scan-dir

This program recursively scans a directory and prompts the users

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

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

E.g.:

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