I said, the shell is my conventional weapons, although not yet proficient, but I love the shell of the language, under Linux mixed, always write a script. Programmers have genes, there is a preference for programming languages, you let me write C code, I will feel very cool, there will be difficulties, there will be painful groping and learning, but I am willing to learn shell/python, I would like to, even lisp this unpopular language I am also full of curiosity, I don't know anything about go and Erlang now, but I'm interested in both languages, and I'll make love to them if I take out my hand. There is love will have hate, I painfully realize that I am a very emotional programmer, even if I scold myself over and over again bitch is bitchy, over and over to tell themselves to correct attitude, learning css/html/still make me miserable, can be expected, Let me learn Java I will also be very painful (I also clearly understand that the fierce pain must not learn css/html pain). I know I digress, I am a cheap, but I repressed too hard, do not find a place to vent, I will be able to suppress the bad.
How do you handle shell programming, which often encounters a situation where the number of parameters is variable? Shift is going to be a shining debut.
$ #是入参的个数,
$@ is all of the current incoming parameters
$ is the name of the script
$ is the first entry, and $ is the second argument ....
Bash defines $9 in total, which determines that we can't get more incoming parameters with $11 and the like.
Now you need to use SHIFT, and shift will move the parameters right, as shown in the following figure:
Let's look at a piece of shell code to deepen our understanding:
Copy Code code as follows:
root@manu:~/code/shell/temp# Cat test.sh
#!/bin/sh
Until [$#-eq 0]
Todo
echo "$@"
Shift
Done
Look at the output:
Copy Code code as follows:
root@manu:~/code/shell/temp#./test.sh 10 9 8 7 6 5 4 3 2 1
10 9 8 7 6 5 4 3 2 1
9 8 7 6 5 4 3 2 1
8 7 6 5 4 3 2 1
7 6 5 4 3 2 1
6 5 4 3 2 1
5 4 3 2 1
4 3 2 1
3 2 1
2 1
1
Now, if the number of participants is uncertain, how do we handle the incoming parameters?
Copy Code code as follows:
Until [-Z ' $] # until all parameters used up
Todo
Store_input $
Shift
Done
The above pseudo code fragment shows how to handle indefinite incoming parameters, and by Store_input, we save each entry, and then we can handle it.
Finally, an example of dealing with indefinite parameters is given:
Copy Code code as follows:
manu@manu:~/code/shell/temp$ Cat sum.sh
#!/bin/sh
Sum=0
Until [Z $]
Todo
Sum= ' echo $sum +$1 |BC '
Shift
Done
Echo $sum
The output is as follows:
Copy Code code as follows:
manu@manu:~/code/shell/temp$./sum.sh 1 2 3 4 5 6 7 8 9 10
55
Reference articles:
Http://www.jb51.net/article/40259.htm
