How to write shell script
Following steps are required to write shell script:
(1) Use any editor like vi
or
mcedit to write shell script.
(2) After
writing shell script
set execute permission for your
script as
follows
syntax:
chmod permission your-script-name
Examples:
$ chmod +x your-script-name
$ chmod 755 your-script-name
Note: This will set read write execute(7) permission for owner, for group and other permission is read and execute only(5).
ls -l command earlier presented a long of listing file with a line like the following for each file:
-rw-r--r-- 1
root user 0
2009-04-28 08:26 newfile.txt
Here the first character in
the first column (-) indicates that the file is a normal file. The next 9 characters indicate the access permissions for the file. The next set of 9 characters is divided into3 groups of
3 cha- racters. Purpose of these characters is as under:
(-) represents no permission
(r) represents 'read' permission
(w) represents 'write' permission
(x) represents 'execute' permission
Permission
|
Octal number
|
Equivalent Symbol
|
Read
|
4
|
r--
|
Write
|
2
|
-w-
|
Execute
|
1
|
--x
|
The three group represents
user (owner
of the
file),
group(to
which
the
owner belongs) and others (any
other user of the system) respectively. Three characters in each group are for 'read', 'write' and 'execute' permission respectively.
In
our example, the owner has 'read' and 'write' permission for the file and everyone else has only read permission. For a normal file, read, write and execute permissions are obvious. For a directory, read and write permissions mean that
to read the contents of
the directory and create new entries in the directory. Execute permission means that one can search in the
directory but not read from or write to the directory.
You can use
the chmod command to change the access permissions of a
file or a directory. To specify permissions for a file with chmod, any of the following two methods can be used.
Symbol
|
Meaning
|
u
|
User
|
g
|
Group
|
o
|
Other
|
a
|
All (equals to ugo)
|
+
|
Add Permission
|
-
|
Remove a permission
|
r
|
Read Permission
|
w
|
Write permission
|
x
|
Execute permission
|
Syntax: chmod u+x filename
(3) Execute your script as
syntax:
bash your-script-name
sh your-script-name
./your-script-name
Examples:
$ bash bar
$ sh bar
$ ./bar
Anurag
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