1. How to write a bash script like the python?
Lloyd Huang
KaLUG - Kaohsiung Linux User Group
COSCUP Aug 18 2012

2. Before the start
Before the start
• About Bash Python and me.
• The ipython and lpython.py.
• A trick, but it touches my heart.
Examples of lpython.py :
cat /etc/passwd | lpython.py
'for i in stdin:n s=i.split(":"); print s[0],s[5],s[6],'
uname -a | lpython.py 'print stdin.read().split()[0:3]'
2

3. Bash: Questions and answers
Bash: Questions and answers
Q: How to be more logic and reuse?
A: Function.
Q: How to do unit testing?
A: Function.
Q: How different is between
Bash function and Python module?
A: ....
3

4. Bash source VS Python import
Bash source VS Python import
Python
• A module allows you to logically organize your Python
code. Grouping related code into a module makes the
code easier to understand and use.
• Python modules are easy to create; they're just files
of Python program code.
• if __name__ == '__main__':
4

5. Bash source VS Python import
How Bash do it?
5

6. Bash source VS Python import
#!/bin/bash | #!/usr/bin/python
funtest() { | def funtest():
echo "func for test" | print "func for test"
} |
funfake() { | def funfake():
echo "func for fake" | print "func for fake"
} |
# main | if __name__ == '__main__':
funtest | funtest()
funfake | funfake()
$> source samp00.sh $> python
func for test >>> import samp00
func for fake
$> bash samp00.sh $> python samp00.py
func for test func for test
func for fake func for fake
6

7. Bash source VS Python import
#!/bin/bash | #!/usr/bin/python
funtest() { | def funtest():
echo "func for test" | print "func for test"
} |
funfake() { | def funfake():
echo "func for fake" | print "func for fake"
} |
return 2> /dev/null | if __name__ == '__main__':
funtest | funtest()
funfake | funfake()
$> source samp00.sh $> python
>>> import samp00
$> bash samp00.sh $> python samp00.py
func for test func for test
func for fake func for fake
7

8. Bash source VS Python import
#!/bin/bash
funtest() {
echo "func for test"
}
funfake() {
echo "func for fake"
}
if [ "$0" == "$BASH_SOURCE" ]; then
funtest
funfake
fi
8

9. From xkcd http://xkcd.com/353/

10. Python module and docstring
Python module and docstring
• import, from
• import module as someone
– Import module
• del
– Delete object
• docstring
– Python Documentation Strings
10

11. Python module and docstring
#!/usr/bin/python
def funtest():
"""
Here is python docstring for funtest.
Here is python docstring for funtest.
"""
print "func for test"
def funfake():
"Here is python docstring for funcfake."
print "func for fake"
if __name__ == '__main__':
funtest()
funfake()
11

12. Python module and docstring
$> python
>>> import samp02
>>> samp02.
samp02.__doc__( samp02.funtest( samp02.funfake(
>>> samp02.funtest()
func for test
>>> help (samp02.funtest)
>>>
Help on function funtest in module samp02:
funtest()
Here is python docstring for funtest.
Here is python docstring for funtest.
12

13. Python module and docstring
>>> samp02.funfake.__doc__
'Here is python docstring for funcfake.'
>>> print samp02.funfake.__doc__
Here is python docstring for funcfake.
>>> import samp02 as new_samp02
>>> new_samp02.funtest()
func for test
>>> del new_samp02
>>> new_samp02.funtest()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'new_samp' is not defined
13

14. Bash import and docstring ?
Bash import and docstring ?
Usage: source import.sh
• import, from
• import module as someone
– Import module
• del module
– Delete module
• help module.function
– Documentation Strings
14

15. Bash import and docstring ?
#!/bin/bash
funtest() {
__doc__="
Here is bash import.sh docstring for funtest
Here is bash import.sh docstring for funtest
"
echo "func for test"
}
funfake() {
__doc__="Here is bash import.sh docstring for funfake"
echo "func for fake"
}
if [ "$0" == "$BASH_SOURCE" ]; then
funtest
funfake
fi
15

16. Bash import and docstring ?
$> source import.sh
$> import samp02.sh
$> samp02
samp02.funfake samp02.funtest
$> samp02.funtest
func for test
$> import samp02.sh as new_samp
$> new_samp.funtest
func for test
$> help new_samp.funtest
Here is bash import.sh docstring for funtest
Here is bash import.sh docstring for funtest
$> del new_samp
$> new_samp.funtest
bash: new_samp.funtest command not found
16

17. uid, gid = split(``1000:100'',``:'') ?
uid, gid = split(``1000:100'',``:'') ?
Python : split
name, passwd, uid, gid, note, homedir, shell =
string.split(www-data:x:33:33:www-data:/var/www:/bin/sh,:)
Bash : read
LDread () {
__doc__=LDread '.' 'V01.01.05.28.KH0.10.28' c1 c2 c3 c4 c5 c6 c7
local ifs con
ifs=$1; shift
con=$1; shift
IFS=$ifs read $@ (echo $con)
}
17

18. 阿宅圖片來源：公立怪咖國民小學 http://blog.xuite.net/protion/school/9142122

19. Hook
Hook
#!/bin/bash
funtest() {
__doc__=Hook test - Part I
PreHook=echo This is PreHook
PostHook=echo This is PostHook
test -n $PreHook $PreHook
echo func for test
test -n $PostHook $PostHook
}
19

20. Hook
$ import hook00.sh
$ hook00.funtest
func for test
$ help hook00.funtest
Hook test - Part I
PreHook=echo This is PreHook
PostHook=echo This is PostHook
$ PreHook=echo This is PreHook
$ PostHook=echo This is PostHook
$ hook00.funtest
This is PreHook
func for test
This is PostHook
20

21. Hook
#!/bin/bash
funtestPreHook () {
return
}
funtestPostHook () {
return
}
funtest() {
__doc__=Hook test - Part II
funtestPreHook () { echo This is funtestPreHook; }
funtestPostHook () { echo This is funtestPostHook; }
funtestPreHook
echo func for test
funtestPostHook
}
21

22. Hook
$ import hook01.sh
$ hook01.funtest
func for test
$ help hook01.funtest
Hook test - Part II
hook01.funtestPreHook () { echo This is funtestPreHook; }
hook01.funtestPostHook () { echo This is funtestPostHook; }
$ hook01.funtestPreHook () { echo This is funtestPreHook; }
$ hook01.funtestPostHook () { echo This is funtestPostHook; }
$ hook01.funtest
This is funtestPreHook
func for test
This is funtestPostHook
22

23. Demo
Demo
23

24. Advantages VS Problems
Advantages VS Problems
• Advantages
– Function reuse
– Unit testing
– Name space
– Documentation strings
– Grouping up commands
• Problems
– To Conflict with ImageMagick
– Can't work with busybox ash
24