Condition Test in Shell

1.test statement

The test instruction is used when I want to detect that some of the file rings on the system are related attributes.

(1) The file type judgment about a filename, such as TEST-E filename indicates existence

-e Does the file name exist? Common

-F does the filename exist and is a file (file)? Common

-D does this "filename" exist and is directory (directory)? (common)-B does the "filename" exist and is a block device device?

-C Does the "filename" exist and is a character device device?

-S does the "filename" exist and is a Socket file?

-P does the filename exist and is a FIFO (pipe) file?

-L does the filename exist and is a link file?

(2) About the permissions of the file detection, such as test-r filename to indicate whether or not (but root permissions are often exceptional)

-R detects if the filename exists and has "read-only" permissions?

-W Detect if the filename exists and has "writable" permissions?

-X detects if the filename exists and has "executable" permissions?

-U detects the existence of the file name and has a "SUID" attribute?

-G detects if the filename exists and has "SGID" properties?

-K detects if the filename exists and has a "Sticky bit" attribute?

-S detects if the filename exists and is "not a blank file"?

(3) Comparison between two documents test File1-nt File2

-nt (newer than) determines whether file1 is newer than file2

-ot (older than) judge whether File1 is older than file2

-ef judge whether File1 and File2 are the same files, can be used to judge hard Link's judgment.

(4) A determination between two integers, such as test n1-eq N2

-eq two values equal (equal)

-ne two values unequal (not equal)

-GT N1 greater than N2 (greater than)

-lt N1 less than N2 (less than)

-ge N1 is greater than or equal to N2 (greater than or equal)

-le N1 is less than or equal to N2 (less than or equal)

(5) The data of the decision string

Test-z string evaluates to 0? True if string is an empty string

Test-n string Determines whether the string is not 0? False if string is an empty string. Note:-n can also be omitted

Test STR1 = str2 determine if str1 equals str2, if equal, return True

Test str1!= str2 determine if str1 is not equal to str2, if equal, return False

(6) Multiple condition determination, for example: Test-r filename-a-x filename

Both the status of-a (and) are simultaneous! For example, Test-r file-a-x file, the file has both R and X permissions to return True.

-O (or) two conditions any one is established! For example, Test-r file-o-x file, the file can return true if it has R or X permissions.

! Reversed phase state, such as test! -x file, which is true when file does not have an X.

Example:

# 1. Let the user enter the filename and determine if the user really has an input string?

ECHO-E "Please input a filename, I'll check the filename ' s type and

Permission. nn

Read-p "Input a filename:" filename

Test-z $filename && echo "You must input a filename." && exit 0

# 2. To determine if a file exists? display a message end script if it does not exist

Test! -E $filename && echo "The filename ' $filename ' do not exist ' &&

Exit 0

# 3. Start to determine file types and attributes

Test-f $filename && filetype= "Regulare file"

test-d $filename && filetype= "directory"

Test-r $filename && perm= "readable"

Test-w $filename && perm= "$perm writable"

Test-x $filename && perm= "$perm executable"

# 4. Start outputting information!

echo "The filename: $filename is a $filetype"

echo "and the permissions are: $perm"

2. Using the judgement symbol []

In addition to the test we like to use, in fact, we can often judge the symbol [] (that is, the brackets) to judge the data! But pay attention to the following points:

(1) Each component in the brackets [] is required to be separated by a space bar;

(2) The number of the hair within the brackets, preferably with double quotation marks in parentheses;

(3) The constants within the brackets, preferably enclosed in single or double quotes.

Example:

#!/bin/bash

Path=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin

Export PATH

Read-p "Please input (y/n):" yn

["$yn" = = "Y"-o "$yn" = "y"] && echo "OK, continue" && exit 0

["$yn" = = "n"-o "$yn" = = "n"] && echo "Oh, interrupt!" && exit 0

echo "I don ' t know what your choice is" && exit 0

Several constants in the 3.shell that are often used in the test

(1) The execution of the script file named $ this variable, the first argument is $, and so on.

(2) $#: Represents the "number" of the following parameters, the $ $ is not counted in it.

(3) $@: Representing "$" "$" "$" "$" means that each variable is independent (enclosed in double quotes).

(4) $*: Represents "" $1c$2c$3c$4 "", where c is the separator character, the default is the space bar, so this example represents "$ $ $ $" meaning.

Example:

The script is as follows:

echo "The script name is ==> $"

echo "Total parameter number is ==> $#"

["$#"-lt 2] && echo "The number of parameter is less than 2. Stop

here. "

&& Exit 0

echo "Your whole parameter is ==> ' $@ '"

echo "the 1st parameter ==> $"

echo "the 2nd parameter ==> $"

Execution results:

[root@www scripts]# sh sh07.sh theone haha quot

The script name is ==> sh07.sh <== file name

Total parameter number is ==> 3 <== three parameters

Your whole parameter is ==> ' theone haha quot ' <== ' all contents of parameters

The 1st parameter ==> theone <== first parameter

The 2nd parameter ==> haha <== second parameter

Note: You can also use shift for parameter offset