Linux comparison operators

use the If statement to determine parameters in Linux shell programming

–b when file exists and is a block file returns true-D when file exists and is a character file returns True-e when pathname exists and is a directory returns true-F when a file or directory pathname specified exists and returns True when file exists and is regular -G when the file or directory specified by pathname is present and the Sgid bit is set to return True-H returns True when file exists and is a symbolic link file, this option is invalid on some old systems-K when the file or directory specified by pathname is present and the "sticky" bit is set to return True-p Return true-r when file exists and is a command pipeline when the files or directories specified by pathname are present and are readable, return true-if file exists with a size greater than 0 o'clock returns true-u when the file or directory specified by pathname is present and the SUID bit is set to return True-W Pathname the specified file or directory exists and returns True when it is executable.　　A directory must be executable for its content to be accessed. -O Returns True when the file or directory specified by pathname is present and is owned by the user specified by the active user ID of the current process.

A more detailed description:
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Operator Description Example

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]

The Linux Shell compares character notation:

    -eq   equals-ne    not equal to-GT    greater than-lt    less than-le equals-ge is greater than or equal to-   z    empty string =    two characters typeface etc! =    two characters unequal-n    non-empty string

String comparison operators (note the use of quotation marks, which is a good way to prevent whitespace from disturbing the code)

    -Z String                 if string length is zero, true             [-Z $myvar]-n string                 If string length is nonzero, true             [-n $myvar] string1 = string2< c5/> true if string1 is the same as string2     [$myvar = one and three] string1! = string2        True if string1 differs from string2     [$ MyVar! = one and 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]

Sample script:

#!/bin/Bash # This script prints a message about your weightifYou give it your # weightinchKilos and hightinchcentimeters. if[ ! $# ==2]; Then 　　 Echo "Usage: $ weight_in_kilos length_in_centimeters"ExitfiWeight=" $"Height=" $"Idealweight=$[$height- the]if[$weight-le $idealweight]; Then 　　 Echo "You should eat a bit more fat." 　　 Else 　　 Echo "You should eat a bit more fruit." 　　 fi# weight.SH  -  MaxYou should eat a bit Morefruit. # weight.SH  -  Max  -Usage:./weight.SHWeight_in_kilos length_in_centimeters position parameter $1, $2,..., $N, $ #代表了命令行的参数数量, $ A represents the name of the script, the first parameter represents the $1, the second parameter represents $2, and so on, the total number of parameters exists $ #中, the above example shows how to change the script, if the parameter is less than or 2 extra to print out a message.　　Execute, and view the situation. # bash-X Tijian.SH  -  the+ weight= -+ height= the+ idealweight= -+'['  --le - ']'+Echo 'You should eat a bit more fat.'You should eat a bit Morefat. Which-X is used to check the execution of the script. Hell Various comparison operators