Miscellaneous: Shell scripts
(last edit: 2000-11-22)
                   #!/bin/sh lets the kernel know that the Bourne Shell will execute the lines in the program
(you can ofcourse specify any shell you want to use)

Debugging a shell script

user@host:~#sh -x [shell script]

This wil display each command and it's output. 

Command substitution:

Is done using backquotes

currentdir = `pwd`

Will have the value of the current working dir

currentdir = pwd

Will have the value "pwd"


If statements

if [ expression ]
then

else

fi

The spaces in [ expression ] must be there!!! If not you get a syntax error

As expression you can use:

int1 -eq int2       Equal
int1 -ne int2       Not equal
int1 -gt int2       Greater than
int1 -ge int2       Greater than or equal to
int1 -lt int2       Less than
int1 -le int2       Less than or equal to

string1 = string2   Equal
string1 != string2  Not equal
string              String is not null
-z string           True if the length of string is zero.
-n string           True if the length of string is non-zero.

-d filename         True if dir exists
-f filename         True if exists as non dir
-s filename         True if contains at least one character

expr1 -a expr2      And
expr1 -o expr2      Or
\( expr \)          Grouping expressions

example: if [ "$answer" = "Y" -o "$answer" = "y" ]


Splitting strings

By default the IFS variable is set to a whitespace, you can reset this ofcourse..

#!/bin/sh

input="this:is:a:test"

printf "\n\n"

IFS=:
for section in $input
do
  printf "$section \n"
done

printf "\n\n"