LINUX Shell Script manual

Relational Operators

-eq - Equal to

-lt - Less than

-gt - Greater than

-ge - Greater than or Equal to

-le - Less than or Equal to

File related tests

-f file - True if file exists and is a regular file.

-r file - True if file exists and is readable.

-w file - True if file exists and is writable.

-x file - True if file exists and is executable.

-d file - True if file exists and is a directory.

-s file - True if file exists and has a size greater than zero.

String tests

-n str - True if string str is not a null string.

-z str - True if string str is a null string.

-s file - True if file exists and has a size greater than zero.

Test also permits the checking of more than one expression in the same line.

-a  - Performs the AND function

-o  - Performs the OR function

$ test -e .
$ echo $?
0 $ test -e xyz
$ echo $?
1

Operator "#" means "delete from the left, to the first case of what follows."

$ x="This is my test string."

$ echo ${x#* }

is my test string.

                   

                   

Operator "##" means "delete from the left, to the last case of what follows."

$ x="This is my test string."

$ echo ${x##* }

string.

                     

                   

Operator "%" means "delete from the right, to the first case of what follows."

$ x="This is my test string."

$ echo ${x% *}

This is my test

                       

                   

Operator "%%" means "delete from the right, to the last case of what follows."

$ x="This is my test string."

$ echo ${x%% *}

This 

IF

#!/bin/bash

if test -e .

then

        echo "Yes."

else

        echo "No."

fi

#!/bin/bash

if [ -e . ]

then

        echo "Yes."

else

        echo "No."

fi

FOR LOOP

#!/bin/bash

for fn in tom dick harry; do

        echo "$fn"

done

#!/bin/bash

for n in {0..5}

do

        echo $n

done

WHILE


#!/bin/bash

n=1

while [ $n -le 6 ]; do

        echo $n

        let n++

done

#!/bin/bash

y=1

while [ $y -le 12 ]; do

        x=1

        while [ $x -le 12 ]; do

               printf "% 4d" $(( $x * $y ))

               let x++

        done

        echo ""

        let y++

done


CASE


#!/bin/bash
echo "What is your preferred programming / scripting language"
echo "1) bash"
echo "2) perl"
echo "3) phyton"
echo "4) c++"
echo "5) I do not know !"
read case;
#simple case bash structure
# note in this case $case is variable and does not have to
# be named case this is just an example
case $case in
    1) echo "You selected bash";;
    2) echo "You selected perl";;
    3) echo "You selected phyton";;
    4) echo "You selected c++";;
    5) exit
esac