COSCUP2012: How to write a bash script like the python?

How to write a bash script like the python?

Lloyd Huang
KaLUG - Kaohsiung Linux User Group
COSCUP Aug 18 2012

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

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

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


How Bash do it?

5


#!/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


#!/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


#!/bin/bash
funtest() {
echo "func for test"
}
funfake() {
echo "func for fake"
}
if [ "$0" == "$BASH_SOURCE" ]; then
funtest
funfake
fi

8

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

Python module and docstring


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

10


#!/usr/bin/python
def 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


$> 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()

12


>>> 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

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


#!/bin/bash
funtest() {
__doc__="
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


$> 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

$> del new_samp
$> new_samp.funtest
bash: new_samp.funtest command not found

16

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

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

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

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

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

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

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

COSCUP2012: How to write a bash script like the python?

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