Shell script parsing 4 ---- branch statement (IF)

I. Condition statements

1,

If [expression]

Then

# Code block

Fi

2,

If [expression]

Then

# Code block

Else

# Code block

Fi

3,

If [expression]

Then

# Code block

Else if [expression] # Replace this field with Elif [expression]

Then

# Code block

Else

# Code block

Fi

Fi

Ii. Comparison of common condition statements

Comparison operation Integer Operation string operation

Same-eq =

Different-ne! =

Greater than-GT>

Less than-lt <

Less than or equal to-le

Greater than or equal to-Ge

Blank-z

Not empty-n

-E: determines whether the file already exists.

-F files are common files.

-S file size is not zero

-D file is a directory

-The R file can be read by the current user.

-W files can be written to the current user

-The X file can be executed on the current user.

For example:

#! /Bin/sh

Folder =/home

[-R "$ folder"] & Echo "can read $ folder" # "&" indicates that when the preceding is true, the following command is executed. It means "that.

[-F "$ folder"] | echo "this is not file" # "|" indicates that when the preceding value is false, the following command is executed. It means "otherwise.