Shell Test []

Http://man.linuxde.net/test
Http://blog.chinaunix.net/uid-24780853-id-2578709.html

[email protected] ~]# man testtest (1) User Commands Test (1) NAME test - Check file types and compare Valuessynopsis Test EXPRESSION t       EST [EXPRESSION] [] [Optiondescription Exit with the status determined by EXPRESSION. --help Display  this help and exit --version output version information and E XIT an omitted EXPRESSION defaults  to false. 
Otherwise, EXPRESSION is true or false and sets exit status. It 's one of  : (expression) EXPRESSION is  true ! expression Expression  is false

If the choice is executed with $? return value About
Test = = []
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[Email protected] ~]# test
[[email protected] ~]# echo $?
1

[[Email protected] ~]# []
[[email protected] ~]# echo $?
1

--------------------------------------------------------------------------

(LS) differs from $ (LS):

(LS) executes the LS command in the child shell, and the screen displays the result

a=$ (LS): The LS executes the command result, that is, the output value is placed in the variable A, redirected output to a (excluding error output)

[[Email protected] kk]# (LS)
Mm
[[email protected] kk]# echo $?
0

[[Email protected] kk]# (LS TT)
LS: Unable to access TT: No file or directory
[[email protected] kk]# echo $?
2

[[email protected] kk]#! Ls
Mm
[[email protected] kk]# echo $?
1

Description "!": Action is $? Take counter

--------------------------------------------------------------------------------------------------------------- --------------

echo $ ((2>1))

1

echo $ ((2==1))

0

echo $ ((2<1))

0

a=$ ((2+1))
b=$ ((2-1))
c=$ ((2*1))
d=$ ((2/1))

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[[email protected] kk]# true
[[email protected] kk]# echo $?
0
[[email protected] kk]# false
[[email protected] kk]# echo $?
1

--------------------------------------------------------------------------

-A :
-o:expression1-a EXPRESSION2 both EXPRESSION1 and EXPRESSION2 aretrueEXPRESSION1-o EXPRESSION2 either EXPRESSION1 or EXPRESSION2 is true
---------------------------------------------------------------------------------------string:
-n String the length of string isnonzero STRING equivalent to-N STRING-Z String The length of string isZero STRING1=STRING2 the strings is equal STRING1!=STRING2 the strings is not equal
------------------------------------------------------------------------------------------------------------Integral type: INTEGER1-eq INTEGER2 INTEGER1 isequal to INTEGER2 INTEGER1-GE INTEGER2 INTEGER1 isgreater than or equal to INTEGER2 INTEGER1-GT INTEGER2 INTEGER1 isgreater than INTEGER2 INTEGER1-le INTEGER2 INTEGER1 isLess than or equal to INTEGER2 INTEGER1-LT INTEGER2 INTEGER1 isLess than INTEGER2 INTEGER1-NE INTEGER2 INTEGER1 isNot equal to INTEGER2
--------------------------------------------------------------------------------------------------------------- ------------------Files: FILE1-EF FILE2 FILE1 and FILE2 have the same device and inode numbers FILE1-NT FILE2 FILE1 isNewer (modification date) than FILE2 FILE1-ot FILE2 FILE1 isolder than FILE2-b file File exists and isBlock Special-c file File exists and isCharacter Special-d file file exists and isa directory-e file file exists-f file File exists and isa regular file-g file file exists and is Set-group-ID-G file file exists and isowned by the effective group ID-h file file exists and isA symbolic link (same as-L)-k file file exists and have its sticky bitSet-L file file exists and isA symbolic link (same as-h)-O file file exists and isowned by the effective user ID-p file File exists and isa named pipe-r file file exists and Read permission isgranted-s file file exists and has a size greater than zero-S file file exists and isa socket-T FD file descriptor FD isopened on a terminal-u file file exists and itsSet-user-id bit is Set-w file file exists and write permission isgranted-x file file exists and execute (or search) permission isgranted
--------------------------------------------------------------------------------------------------------------- ----------------Except for-H and-l, all file-related tests dereference symbolic links. Beware that parentheses need to being escaped (e.g., by backslashes) forShells. INTEGER may also is-l string, which evaluates to the length of string. Note: [Honors the--help and--version options, but test does not. Test treats each of the those asit treats any other nonempty STRING. Note:your Shell May has its own version of Test and/or [, which usually supersedes the version described here. Refer to your shell ' s documentation forDetails about the options it supports.

Shell Test []