Shell condition judgment

Conditional judging Type

As long as the procedure, then the conditional judgment, that is, if then this discriminant must be learned, the other is Case...esac

If....then

This is If...then is the most common conditional judgment, it is divided into single-branch conditional judgment, double-branch conditional judgment, multi-branch conditional judgment type

Single-branch conditional judgment statement:

If [conditional judgment]

Then

Output content

Fi

Two-branch conditional judgment:

If [conditional judgment]

Then

Output content

Else

Output content

Fi

Multi-branch conditional judgment

If [conditional judgment]

Then

Output content

elif [Conditional Judging type]

Then

Output content

Else

Output content

Fi

There are 3 common methods for the comparison of conditional judgments, namely, numerical comparison, character comparison, and file comparison.

Numerical comparison:

Integer comparison

-EQ: Tests whether two integers are equal, such as $a-eq $B

-ne: Test whether two integers are unequal: unequal, true: equal, False

-GT: Tests whether a number is greater than another number: greater Than, true: otherwise, false

-LT: Tests whether one number is less than the other: less Than, true: otherwise, false

-ge: greater than or equal to

-le: Less than or equal to

Character comparison:

STRING1 = STRING2: Indicates equal characters

STRING1! = STRING2: Indicates unequal characters

File comparison:

-E: Indicates whether the file exists

-F: Indicates that the file exists and is a normal file

# #还有很多选项, the above two are more commonly used

Exercise: Write a script

Determine if there is a user default shell for bash on the current system:

If so, how many of these users are displayed: otherwise, no such user is shown

[Email protected]_2 ~]# Cat ba.sh

#!/bin/bash

Bashuser= ' grep ' \<bash\> "/etc/passwd |cut-d": "-F 1 '

If [$?-eq 0];then

echo "The following users have bash:"

echo "${bashuser}"

Else

echo "No user has bash"

Fi

Exercise: Write a script

Given a file, such as/etc/inittab

Determine if there is a blank line in this file

If available, displays the number of blank lines: Otherwise, no blank lines are displayed

[Email protected]_2 ~]# Cat hang.sh

#!/bin/bash

hang= ' grep ' ^$ '/etc/inittab |wc-l '

If [! $?-eq 0];then

Exit 8

Fi

If [$hang-gt 0];then

echo "has ${hang} row blank line"

Else

echo "No blank line"

Fi

Exercise: Write a script

Given a user, determine if the UID is the same as the GID

If it does, the user is displayed as "good guy": Otherwise, this user will be shown as "bad guy"

[Email protected]_2 ~]# Cat ug.sh

#!/bin/bash

Useruid= ' id-u ' [email protected] ' 2>/dev/null '

If [! $?-eq 0];then

echo "Please pass in the correct user"

Exit 9

Fi

Usergid= ' id-g ' [email protected] ' 2>/dev/null '

If [! $?-eq 0];then

echo "Please pass in the correct user"

Exit 9

Fi

If [$#-eq 1];then

If [$useruid-eq $usergid];then

echo "Good guy"

echo "${1} UID and GID"

Else

echo "Bad guy"

Fi

Else

echo "Please pass in the correct parameters"

Fi

Exercise: Write a script

Determines whether the total number of history commands in the command history is greater than 1000, if greater than, displays "Some command will Gone": Otherwise "OK" is displayed.

[Email protected]_2 ~]# Cat his.sh

#!/bin/bash

#

his= ' History |wc-l 2>/dev/null '

If [$his-gt];then

echo "Some command would gone"

Else

echo "OK"

Fi

Case....esac judgment

Grammar

Case variable name in

Value one)

Output information

;;

Value two)

Output information

;;

*)

Output information

;;

Esac

#一般常用于传参

This article is from "think one or two" blog, please be sure to keep this source http://250919938.blog.51cto.com/962010/1918592

Shell condition judgment