Shell Learning notes-conditional judgment

1. Judging the format

1) Test parameter file

Example: Test-e/root/install.log

2) [parameter file]--Recommended use

Example: [-e/root/install.log]

Note: Spaces are required after and before the brackets

2. determine file type parameters

1)-D file: Determine if the file exists and whether it is a directory file

2)-e file: Determine if the file exists

3)-F file: Determine if the file exists and is a normal file

4)-S file: Determine if the file exists and is not empty

5) Other file type judgment:

-B block device file;-c character device file;-l symbolic link file;-p pipe file;-S socket file

Example:

Echo Echo  ~]# [-e/root/installechoecho~]# [-f/root/installEcho  Echo~]# [-s/root/installechoecho  Noyes

3. Determine file permission parameters

1)-R file: Determines if the file exists and has Read permission

2)-W file: Determine if the file exists and write permission

3)-X file: Determines if the file exists and has execute permissions

4) Other file permissions to judge:

-u suid permissions;-g sgid permissions;-k sbit permissions

Example:

[[Email protected] ~]# [-r/root/installechoecho~]# [-w /root/  Installechoecho ~]# [-x/root/installechoecho Nono

4. Comparison of two files

1) file 1-nt file 2: Determine if file 1 modification time is newer than file 2

2) file 1-ot file 2: Determine if the modification of file 1 is older than file 2

3) file 1-ef File 2: Determine whether the file 1 is the same as the lnode of file 2, it can be understood that two files are the same file. This judgment is a good way to judge hard links.

Example:

[Email protected] ~]# [/root/install. log-nt/root/Installechoecho~]# [/root/Installlog-ot/root/installechoecho~]# [/root/Install . log-ef/root/Installechoecho  Nono

5. Comparison of two integers

1) Integer 1-eq integer 2: determine equality

2) Integer 1-ne integer 2: Determines whether inequality is not equal

3) Integer 1-GT integer 2: Determine if it is greater than

4) Integer 1-LT integer 2: Determines whether it is less than

5) Integer 1-ge integer 2: Determines whether it is greater than or equal to

6) Integer 1-le integer 2: Determines whether it is less than or equal to

Note: In the shell, all variables are character types, but an integer comparison parameter is added, and the variables on both sides are considered integer types.

Example:

[Email protected] ~]# [1-eq1] &&EchoYes | |EchoNoyes[[email protected]~]# [1-ne1] &&EchoYes | |EchoNono[[email protected]~]# [2-gt1] &&EchoYes | |EchoNoyes[[email protected]~]# [2-lt1] &&EchoYes | |EchoNono[[email protected]~]# [1-ge1] &&EchoYes | |EchoNoyes[[email protected]~]# [1-le1] &&EchoYes | |EchoNoyes

6. String Judgments

1)-Z string: Determine if the string is empty

2)-N string: Determines whether the string is not empty

3) String 1 = = String 2: Determine if two strings are equal

4) String 1! = String 2: Determines whether two strings are not equal

Example:

[Email protected] ~]# str="ABC"[[Email protected]~]# [-Z $str] &&EchoYes | |EchoNono[[email protected]~]# [-N $str] &&EchoYes | |EchoNoyes[[email protected]~]# str2="EFG"[[Email protected]~]# ["$str"=="$str 2"] &&EchoYes | |EchoNono[[email protected]~]# ["$str"!="$str 2"] &&EchoYes | |EchoNoyes

7. Multiple conditional judgments

1) Judge 1-a Judgment 2: The expression of logic and, equivalent to and

2) Judging 1-o Judgment 2: Representation of logic or, equivalent to or

3)! Judgment: Indicates logical non, equivalent to not

Example:

1 1 1 2  Echo Echo  1112  echoecho1  2  echoecho  Noyes

Shell Learning notes-conditional judgment