6 shell tips to make the script no longer amateur

Former colleague Wang Xiao has published a book ,《 Starting from scratch Linux Operation and maintenance practice 》, Let him send me a copy .

After reading the book , I said, , Your book is not “ On the tall ” ah , speak Linux, Say command tool set , speak vim, speak shell Programming , speak awk practice ... Want to sell , Don't you have a whole new term of high technology ？

Wang Xiao said , We don't know much about new high-tech terms , You can't scare others , Instead, I flustered myself , It's better to be honest , Let the technical people who love learning have a few gains ...

The following is what I learned from Wang Xiao 6 Practice （ Listen to Wang Xiao , He's with me, too Google learn ）, this , It's also the style of his new book .

Voice over ： The new book is on the shelves , Discount at the end of the article , Welcome to .

How to make your own shell Not so Amateur ？

Share 6 Practice .

One 、 Start with the following sentence

set -o nounset

By default , Encountered a variable that doesn't exist , Will ignore and continue to execute , And that's often not what you expect , Add this option , It can prevent the consequences from spreading , Terminate execution of script .

Voice over ： Some mistakes in variable names , It's going to take a long time to debug , In this way , This kind of hand Miss second detection .

set -o errexit

By default , Encountered execution error , Will skip and continue to execute , And that's often not what you expect , Add this option , It can prevent the consequences from spreading , Terminate execution of script .

Voice over ： There are some Linux command , for example rm Of -f Parameters can force errors to be ignored , At this point, the script cannot capture errexit, Such parameters are not recommended in scripts .

These two options , All conform to fail fast Design concept .

Two 、 It is necessary to encapsulate functions

Don't patronize and write down , Encapsulation can improve reuse .

As in the above example ：

log()

Simple packaging , Can save a lot of

[$(date +%Y/%m/%d\ %H:%M:%S)]

Duplicate code for .

Voice over ： This log() I little interesting , Have you learned ？

meanwhile , Encapsulation can also improve the readability of the code .

As in the above example ：

ExtractBashComments

Than

egrep "^#"

It's much more readable .

Voice over ： Some friends will say , I don't know English .

3、 ... and 、 Use readonly and local Modifying variables

readonly

seeing the name of a thing one thinks of its function , read-only .

local

Variables within a function .

Don't try to save time , While improving security , Can avoid a lot of people to collapse of the inexplicable mistakes . Is the script written professionally , It's not a high point , But the embodiment of basic skills .

Voice over ： It is said that , One C++ What level of programmers , from ta In the code const How often do you use it , Can see .

Four 、 Use $() Instead of `( Back single quotes )

Why? ？ Look at the example above and you will understand ：

（1）$() Can support embedded ;

（2）$() No need to escape ;

（3） Some Fonts ,`( Back single quotes ) and ’( Single quotation marks ) It's like , It's easy to confuse people ;

5、 ... and 、 Use [[]] Instead of []

Use single brackets ：

Use double brackets ：

See the difference ？[[]] More in line with the human code ：

（1） Avoid escape problems ;

（2） There are many new features ;

New features include, but are not limited to ：

|| ： Logic or

&& ： Logic and

< ： String comparison （ There is no need to escape ）

== ： wildcard (globbing) String comparison

=~ ： Regular expressions (regular expression, RegEx) String comparison

It should be noted that , from bash3.2 Start , Neither wildcards nor regular expressions can be enclosed in quotation marks （ therefore , The above example , Quotation marks are literal comparisons ）.

So if there's a space in the expression , It has to be stored in a variable , Then compare the wildcard with the regular .

6、 ... and 、echo It's not the only way to debug

It can be used -n Check the syntax of the script .

It can be used -v Tracking the execution of each command in the script .

It can be used -x Tracking the execution of each command in the script , And add expanded information .

Of course , It can also be in scripts , add to

set -o verbose

set -o xtrace

To permanently specify the output debug information .

Voice over ： Try more on the machine and you'll see .

Former colleague Wang Xiao's new book , learn Linux, learn shell, learn awk, learn vim, Learn the operation and maintenance tool set ... Not so much “ On the tall ” The noun , Only dry goods knowledge points ...

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research ：

Do you think Linux,shell,awk,vim Is it necessary for engineers to know and master ？

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