Common statements for Linux shell scripts

Linux shell directives such as-D,-F,-e are judged by :

File comparison Operators
-e filename true if filename exists [-e/var/log/syslog]
-D filename True if filename is a directory [-d/tmp/mydir]
-F filename True if filename is a regular file [-f/usr/bin/grep]
-L filename True if filename is a symbolic link [-l/usr/bin/grep]
-R filename True if filename is readable [-r/var/log/syslog]
-W filename if filename is writable, true [-w/var/mytmp.txt]
-X filename is true if filename is executable [-l/usr/bin/grep]
Filename1-nt filename2 If filename1 is newer than filename2, then true [/tmp/install/etc/services-nt/etc/services]
Filename1-ot filename2 If filename1 is older than filename2, then true [/boot/bzimage-ot Arch/i386/boot/bzimage]
String comparison operators (note the use of quotation marks, which is a good way to prevent whitespace from disturbing the code)
-Z String True if string length is zero [-Z ' $myvar ']
-N String if string length is nonzero, true [-n ' $myvar ']
string1= string2 If string1 is the same as string2, then true ["$myvar" = "One of the three"]
string1!= string2 If string1 differs from string2, true ["$myvar"! = "one, three"]
Arithmetic comparison operators
Num1-eq num2 equals [3-eq $mynum]
Num1-ne num2 Not equal to [3-ne $mynum]
Num1-lt num2 less than [3-lt $mynum]
Num1-le num2 less than or equal to [3-le $mynum]
NUM1-GT num2 greater than [3-GT $mynum]
Num1-ge num2 greater than or equal to [3-ge $mynum]

Reference: http://blog.csdn.net/sxzlc/article/details/7542603

Linux Shell Case statement:

The case statement is suitable for applications that require multiple branching.

The case Branch statement is formatted as follows:

Case $ variable name in

Mode 1)

Command sequence 1

;;

Mode 2)

Command Sequence 2

                      ;;

*)

Sequence of commands executed by default ;;

Esac

The case statement has the following structural characteristics:

The case line end must be the word "in", and each pattern must be terminated with a closing parenthesis ")".

Double semicolon ";;" Indicates the end of the command sequence.

The matching pattern uses square brackets to denote a contiguous range, such as [0-9]; Use the vertical bar symbol "|" Represents or.

The Last "*)" represents the default mode, and when the variable is not matched using the preceding modes, "*" is executed

Sequence of commands.

For example:

1    Case " $" inch                                  //Judge $2*.sh)//if it is a. sh file, then perform this one3# Source Shell Script forSpeed . 4         (                                                                       5Trap-INT QUIT TSTP6scriptname=$1                                                       7 Shift8 . $scriptname9         )                                                                       Ten         ;;  One*)//if it is not. SH then perform this default A         "[email protected]"                                                                     -         ;;  -Esac

Reference Source: http://blog.csdn.net/dreamtdp/article/details/8048720

Linux shell parameters:

$ $ represents the first parameter.

The $ $ represents the second argument.

$ $ represents a third parameter.

[email protected] represents all parameters, this is the way the array is represented by all parameters.

$# represents the number of parameters.

$* can also represent all the parameters.

Common statements for Linux shell scripts