Shell logical operators, logical expressions

Logical symbols

1. about the file and directory of the detection of Logical volume label!

- F Common! Detect if "Archive" exists eg:if [-f filename]

- D common! Detects if the directory exists

- B detection is a "block file"

- C detection is a "character file"

- s detection is a "socket tag file"

- L detection is a "symbolic Link's profile"

- E detects if "something" exists!

2. about the program's Logical volume label!

- g detection is owned by the program performed by the GID

- o detection is owned by the program executed by the UID

- P detects if a name pipe or FIFO is being transmitted between programs (to be honest, this is not a good idea!) ）

3. about the property of the file detection!

- R to detect if a property is readable

- w detection is a property that can be written

- x detect whether the property is executable

- s detection is a "non-blank file"

- U detect if a property with "SUID"

- g detection for properties with "SGID"

- K detect if there is a property of "sticky bit"

4. judgment and comparison between two files; for example [Test file1-nt file2]

-nt The first file is newer than the second one.

-ot The first file is older than the second one.

-ef The first file is the same file as the second file (link and other files)

5. logical "and" "or (OR)"

The meaning of && logic

|| The meaning of a logical OR

Operation symbols

= equals applies To: integer or string comparison if in [], only the string

! = is not equal to: integer or string comparison if in [], only the string

< less than applied: integer comparison in [], cannot use the representation string

> greater than applied: integer comparison in [], cannot use the representation string

-eq equals applies To: integer comparison

-ne Not equal to: integer comparison

-lt less than applied to: integer comparison

-GT greater than applied: integer comparison

-le less than or equal to: integer comparison

-ge greater than or equal to: integer comparison

- A both are established (and) logical Expressions –a logical expressions

- o unilateral formation (or) logical expression –o logical expression

- Z empty string

- N non-empty string

This article is from the "Linux_woniu" blog, make sure to keep this source http://llu1314.blog.51cto.com/5925801/1965332

Shell logical operators, logical expressions