Shell Learning Summary (I.)

#！ /bin/bash

#

The head can not be less, called the magic number, tell the computer is a shell script, with bash to execute it, otherwise unrecognized.

Shell script file to end with. SH, not necessary, just good identification, specification.

1.if condition judgment

if condition; then

The action performed

elif conditions; then

The action performed

Else

The action performed

Fi

If then the line, you can not write ";", but if you do not wrap, you have to ";" Seal No.

2. Conditional test Expressions

[expression] or test expression, note: [Space expression space], space can not be less

A. Integer comparison

-GT is greater than, greater than true

-eq equals

-ne Not equal to

-lt less than

-ge greater than or equal to

-le less than or equal to

B. Document judgement

-E exists, directories can also

-D Directory

-F Normal File

-r,-w,-x, do you have the appropriate permissions

C. Character testing

= = is equal, an equal sign can also [space "" Space = = Space "" Space ") equals must have spaces at both ends

！ = Unequal

>,< greater than, less commonly used

-N string is empty

-S non-null

3.for Cycle

for variable in list; Do

Cyclic action

Done

A. Generation of lists

{value, Value .... }

Implemented with the SEQ command

Seq Start number Step length end number of which the step length and the starting number can be saved, default starting from 1, use the note command with the anti-quote or $ () call

This article from "ayf755" blog, declined reprint!

Shell Learning Summary (I.)