Shell logical operations Summary, including [[]] and [] difference between,&& and-A, | | The difference from-O

1. about Files and directories

-F to determine if an ordinary file exists

-D to determine if a directory exists

-B Determine if a file is a block device

-C Determine if a file is a character device

-S to determine if a file is socket (pending correction)

-l Determine if a file is a symbolic link (pending correction)

-E To determine if something is present (pending correction)

-P to determine if a file is a pipe or FIFO

2. About the properties of a file

-R to determine if the file is a readable property

-W to determine if the file is a writable property

-X to determine whether the file is an executable property

-S to determine whether the file is a non-blank file

-U determines whether the file has suid properties

-G to determine if the file has Sgid properties

-K to determine if the file has a sticky bit attribute

3. 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 as the second file (link and other files)

4. Logical (and) and (or)

&& logical AND Meaning,-A is also the meaning of

|| Logical OR means,-O is also the meaning of

5. Operator-related

Operational symbols represent meaning

= 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

6.1 Test Command

# test 1 = 1 && echo ' OK '

Ok

# test-d/etc/&& echo ' OK '

Ok

# test 1-eq 1 && echo ' OK '

Ok

# if Test 1 = 1; Then echo ' OK '; Fi

Ok

Note: All characters are separated from the logical operators directly with "spaces" and cannot be joined together. Test 1=1 is wrong!

6.2 [] Expression

# [1-eq 1] && echo ' OK '

Ok

# [2 < 1] && echo ' OK '

-bash:2: No such file or directory

# [2 \< 1] && echo ' OK '

# [2-GT 1-a 3-lt 4] && echo ' OK '

Ok

# [2-GT 1 && 3-lt 4] && echo ' OK '

-bash: [: Missing '] '

Note: In the [] expression, the common, < need to add an escape character, representing the string size comparison, Acill code position as a comparison.

Do not directly support <, > Operators, and logical operators | | , && it needs to be represented by-a[and]–o[or]

6.3 [[]] expressions

# [1-eq 1] && echo ' OK '

Ok

# [[2 < 3]] && echo ' OK '

Ok

#[[2 < 3 && 4 > 5]] && echo ' OK '

Ok

[[2 < 3-a 3 > 4]] && echo "OK"

-bash:syntax Error in conditional expression

-bash:syntax error near '-a '

Note: the [[]] operator is only an extension of the [] operator. The ability to support the <,> symbol operation does not require an escape character, it is also a string comparison size. Logical operators are supported inside: | | &&, no longer using-a-o

Gorgeous split Line

*************************************************************************************************************** *******************************

Another part of the summary:

The difference between [[]] and [] in a bash shell

One, [[with "&&" instead of "-a" for logic "and", with "| |" Instead of "-O" means logical "or":

# [[1 < 2 && B > A]] && echo true | | echo False

True

# [[1 < 2-a B > A]] && echo true | | echo False

Bash:syntax Error in conditional expression

Bash:syntax error near '-a '

# [1 < 2-a B > A] && echo true | | echo False

True

# [1 < 2 && B > A]&& echo true | | echo false #wrong syntax

BASH: [: Missing '] '

False

Two, [...] As a shell command, so the expression in it should be its command-line argument, so the string comparison operator ">" and "<" must be escaped, otherwise it becomes an IO redirect operator. [Middle < and > do not need to be escaped:

# [2 \<] && echo true | | echo false #you should use "\<"

False

#[2-lt] && echo true | | echo False

True

# [[2 <]] && echo true | | echo False

False

Three, [[...]] Perform arithmetic expansion, while [...] Do not do.

# [[99+1-eq]] && echo true | | echo False

True

# [99+1-EQ] && echo true | | echo False

BASH: [: 99+1:integer expression expected

False

# [$ ((99+1))-eq] && echo true | | echo False

True

Four, [[]] can use the regular, and [] not

# ["test.php" = = *.php] && echo true | | echo False

False

# [["test.php" = = *.php]] && echo true | | echo False

True

# [["t.php" = = [a-z].php]] && echo true | | echo False

True

# ["test.php" = = "*.php"] && echo True | | echo False

False

# [["test.php" = = "*.php"]] && echo true | | echo False

False

Note: The effect of double quotation marks ("")

This article is from the "Cold River Exclusive Fishing" blog, please be sure to keep this source http://iter2012.blog.51cto.com/6873825/1613696

Shell logical operations Summary, including [[]] and [] difference between,&& and-A, | | The difference from-O