Shulou(Shulou.com)06/01 Report--

Judgment parameters in if statements used in shell programming

-b returns true when file exists and is a block file

-c returns true when file exists and is a character file

-d returns true when pathname exists and is a directory

-e returns true if the file or directory specified by pathname exists

-f returns true when file exists and is a regular file

-g returns true when the file or directory specified by pathname exists and the SGID bit is set

-h returns true when file exists and is a symbolic link file, this option is not valid on some older systems

-k returns true when the file or directory specified by pathname exists and the "sticky" bit is set

-p returns true when file exists and is a command pipeline

-r returns true when the file or directory specified by pathname exists and is readable

-s returns true when the file size is greater than 0 in file

-u returns true if the file or directory specified by pathname exists and the SUID bit is set

-w returns true when the file or directory specified by pathname exists and is executable. A directory must be executable to be accessed for its contents.

-o returns true when the file or directory specified by pathname exists and is owned by the user specified by ID, a valid user of the current process.

Compare the characters written in UNIX Shell:

-eq equals

-ne is not equal to

-gt is greater than

-lt less than

-le less than or equal to

-ge greater than or equal to

-z empty string

= two characters are equal

! = two characters are different

-n non-empty string

A more detailed explanation:

Operator description example

File comparison operator

-e filename true if filename exists [- e / var/log/syslog]

-d filename true if filename is a directory [- d / tmp/mydir]

-f filename True [- f / usr/bin/grep] if filename is a regular file

-L filename is true if filename is a symbolic link [- L / usr/bin/grep]

-r filename true if filename is readable [- r / var/log/syslog]

-w filename is true if filename is writable [- w / var/mytmp.txt]

-x filename true if filename is executable [- L / usr/bin/grep]

Filename1-nt filename2 is true if filename1 is newer than filename2 [/ tmp/install/etc/services-nt / etc/services]

Filename1-ot filename2 is true if filename1 is older than filename2 [/ boot/bzImage-ot arch/i386/boot/bzImage]

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

-z string true [- z $myvar] if string length is zero

-n string true [- n $myvar] if the string length is non-zero

String1 = string2 true if string1 is the same as string2 [$myvar = one two three]

String1! = string2 true if string1 is different from string2 [$myvar! = one two three]

Arithmetic comparison operator

Num1-eq num2 equals [3-eq $mynum]

Num1-ne num2 is not equal to [3-ne $mynum]

Num1-lt num2 is less than [3-lt $mynum]

Num1-le num2 is less than or equal to [3-le $mynum]

Num1-gt num2 is greater than [3-gt $mynum]

Num1-ge num2 is greater than or equal to [3-ge $mynum]

Example script:

#! / bin/bash

# This script prints a message about your weight if you give it your

# weight in kilos and hight in centimeters.

If [! $# = = 2]; then

Echo "Usage: $0 weight_in_kilos length_in_centimeters"

Exit

Fi

Weight= "$1"

Height= "$2"

Idealweight=$ [$height-110]

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 70 150

You should eat a bit more fruit.

# weight.sh 70 150 33

Usage:. / weight.sh weight_in_kilos length_in_centimeters

The location parameter $1, $2dr., $N # represents the number of arguments on the command line, and $0 represents the name of the script.

The first parameter represents $1, the second parameter represents $2, and so on, the total number of parameters exists in $#, and the above example shows how to change the script to print a message if there are fewer or more parameters.

Execute and check the situation.

# bash-x tijian.sh 60 170

+ weight=60

+ height=170

+ idealweight=60

+'['60-le 60']'

+ echo 'You should eat a bit more fat.'

You should eat a bit more fat.

Where-x is used to check the execution of the script.

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