Shell condition Test

File Status Test

-B filename	Returns True when filename exists and is a block file (returns 0)
-C filename	Returns True when filename exists and is a character file
-D Pathname	Returns True when pathname exists and is a directory
-E Pathname	Returns True when a file or directory specified by pathname is present
-F filename	Returns True when filename exists and is a regular file
-G pathname	Returns True when the file or directory specified by pathname exists and the Sgid bit is set
-H filename	Returns True when filename exists and is a symbolic link file (or-l filename)
-K Pathname	Returns True when a file or directory specified by pathname exists and the "sticky" bit is set
-P filename	Returns True when filename exists and is named pipe
-R Pathname	Returns True when a file or directory specified by pathname exists and is readable
-S filename	Returns True when filename exists and the file size is greater than 0 o'clock
-S filename	Returns True when filename exists and is a socket
-T FD	When FD is a file descriptor associated with a terminal device, it returns true
-U pathname	Returns True when the file or directory specified by pathname exists and the SUID bit is set
-W Pathname	Returns True when a file or directory specified by pathname exists and is writable
-X Pathname	Returns True when a file or directory specified by pathname exists and is executable
-O Pathname	Returns True when a user owned by a valid user ID of the current process exists and is pathname (Letter O Uppercase)
-G pathname	True when a user group that is present by pathname and that is part of the current process's valid user ID is returned
File1-nt File2	File1 than File2 new when return True
File1-ot File2	File1 than file2 back to true
F1-EF F2	Files F1 and F2 is hard links to the same file

Example: if [-b/dev/hda]; then echo "yes"; else echo "no"; fi//will print Yes

Test-c/dev/hda; echo $? Will print 1 to indicate that the return value of the test command is 1,/DEV/HDA not a character device

[-W/ETC/PASSWD]; echo $? See if the passwd file is writable for the current user

Test-time logical operator

-A	Logical AND, both sides of the operator are true, the result is true, otherwise false.
-O	Logical OR, the operator side is true, the result is true, otherwise false.
!	Logical No, the condition is false and the result is true.

Example: [-w Result.txt-a-W Score.txt]; echo $? Test whether two files are writable

Common string tests

-Z String	string is empty (length 0) returns True
-N String	Returns True when string strings are non-empty strings
STR1 = str2	Returns True when String str1 and string str2 are equal
STR1 = = str2	same =
Str1! = str2	Returns True when String str1 and string str2 are not equal
STR1 < STR2	Sort by dictionary order, string str1 before string str2
str1 > STR2	Sort by dictionary order, string str1 after string str2

Example: Name= "ZQF"; [$name = "ZQF"];echo $? Printing 0 means the value of the variable name and the string "ZQF" are equal

Common numerical tests

Int1-eq Int2	If Int1 equals Int2, returns the true
Int1-ne Int2	Returns true if Int1 is not equal to Int2
Int1-lt Int2	If Int1 is less than Int2, returns true
Int1-le Int2	Returns True if Int1 is less than or equal to Int2
INT1-GT Int2	If Int1 is greater than Int2, returns true
Int1-ge Int2	Returns true if Int1 is greater than or equal to Int2

Tests in (()):

<	Less than (used in double brackets)	(("$a" < "$b"))
<=	Less than equals (used in double brackets)	(("$a" <= "$b"))
>	Greater than (used in double brackets)	(("$a" > "$b"))
>=	Greater than or equal (used in double brackets)	(("$a" >= "$b"))

Example: x=1; [$x-eq 1]; echo $? Printing 0 means that the value of the variable x equals the number 1 x=a; [$x-eq "1"]//Shell print error message [: A:integer expression expected

Test, [], [[]]

Because the shell differs from our usual programming language, it's more about interacting with it and always calling someone else. So some of the concepts that are part of the programming language itself can be difficult to understand in the shell. "Basic skills" is not good, more easily "sleepy", I am a:-).

Take bash for example (similar to other compatible shells):

1. Test and [is the internal command of bash, the coreutils package of the Gnu/linux system usually also takes/usr/bin/test and/usr/bin/[commands. If we don't specify the absolute path, we usually use Bash's own commands.
2. [[Is the key word of the BASH program language!]

$ ls-l/usr/bin/[/usr/bin/test-rwxr-xr-x 1 root root 37400  September 15:25/usr/bin/[-rwxr-xr-x 1 root root 33920  September 15:25/usr/bin/test$ type [[[[Test[is a shell builtin[[are a shell keywordtest is a shell builtin

In most cases, this three function is common. But commands and keywords are always different. How big is the difference between a command and a keyword?

If it is a command, it is interpreted by the shell as a combination of parameters, such as ">" < "is interpreted by the shell as the redirect symbol." Keywords are not.

Use && in [[] | |

[Use-A and-O are used to represent logic and logic or.

[You can use wildcard characters in

arch=i486[[$arch = i*86]] && echo "Arch is x86!"

[[Match string or wildcard character, no quotation marks required

    [[$arch _com = i386 | | $ARCH = i*86]] &&    cat >> $TFS _repo <<eof[tfs-i386]name=gtes11.3 Prelim1bas Eurl=${baseurl}i386/enabled=1eof

Shell condition Test