Shell Learning Condition test (refer to Shell scripting tricks)

1 about test testing, see the man documentation

The judgment of an expression

(EXPRESSION) #EXPRESSION is True

! EXPRESSION #EXPRESSION is False

Expression1-a EXPRESSION2 #both is true,-o means or

Whether the string is empty, equal

-N string #the length of string is nonzero,-n can removed

-Z String #the length of string is zero (nonexists,or null)

#when comes to string, we use =

STRING1 = STRING2 #the Strings is equal

STRING1! = STRING2 #the strings is not equal

Comparison of Numbers

#when comes to number,we with different EQ ne and so on

Integer1-eq INTEGER2 #INTEGER1 is equal to INTEGER2

-ge Greater or equal

-GT Greater than

-le-lt-ne I

compare files as linked files   

File1-ef FILE2 #FILE1 and FILE2 have the same device and inode numbers

eg

    [[email protected] shell]# test  txt  -ef txthardlink             
                [[email protected] shell]# echo $?
                0
                [[email protected] shell]# test  txt  -ef txtlink(soft)
                [[email protected] shell]# echo $?
                0

So this is whether the test is a file link (including soft and hard), you can try it yourself

Compare the modified time of a file

File1-nt FILE2#FILE1 is newer/older (modification date) than File2,timestamp

File1-ot FILE2 file has a modified time modify time (emphasis on content changes) change times (nature is related to property changes) Contact times Access Time (accessed)

File type

-B FILE #type: Block Special

-C FILE #type: Character Special

-D FILE # a directory

-e FILE #FILE whether exists exists

-S FILE #FILE exists and has a size greater than zero is empty

-F File #a regular file

-U FILE #set user-id SUID

-G file #FILE exists and is Set-group-id temporarily owning the permissions of the group to which the file belongs Sgid

-G FILE #FILE exists and is owned by the effective group ID true Group

-H FILE #a symbolic link (same as-l)

-K FILE #FILE exists and have its sticky bit set sticky bit other users can only add cannot delete

-L FILE #FILE exists and is a symbolic link (same as-h)

-O FILE #FILE exists and is owned by the effective user ID

-P FILE #a named pipe

-S FILE #FILE exists and is a socket

-R FILE #FILE exists and Read permission is granted

You can use-w, write,-X Execute

-T FD #file descriptor FD is opened on a terminal

A lot, but there are regular, not much used

2 The above test can also be used in a similar [-e $num] Structure

3 If/then condition test structure (also case,while, etc structure may be involved later, do not understand please Baidu)

①if [Condition]

Then

COMMAND

Fi

Or

if [Condition];then

COMMAND

Fi

②if [Condition];then

COMMAND1

Else

COMMAND2

Fi

③if [Condition];then

COMMAND1

elif [Condition];then

COMMAND2

Else

COMMAND3

Fi

Big eg.

#if1.sh
#!/bin/bash
#
read -p "guss who am i?"  HELLO
test -z $HELLO&&echo "wrong argv please reinput!"&&exit 1
if [ "$HELLO" = "Jack" ];then
echo "oh,you are jack!"
elif [ "$HELLO" = "Kitty" ];then
echo "oh,you are Kitty!"
elif [ "$HELLO" = "Mike" ];then
echo "oh,you are Mike!"
else
echo "sorry i don‘t remember."
echo "ok,my name is $HELLO"
fi

Usually if then can be changed to [[Conditon]]&& Condition ok| | Condition NOT OK

3 the difference between [[]] and []

Usually manifested in the following aspects

[] Use-a,-o to connect multiple logical expressions, while [[]] using &&,| | Concatenate multiple expressions

[]: Wildcards do not work, [[]] exhibition opening wildcards

[] You cannot use comparison operators, such as >,&LT, while [[]] can

4 (())

To test a numeric expression

The result is 0 returns 1, the result is the other return 0

[Email protected] ~]# ((1-1))

[[email protected] ~]# echo $?

1

[Email protected] ~]# ((+))

[[email protected] ~]# echo $?

0

5 Procedures for judging and testing conditions

# -N can indicate whether the file has been modified
#So there is a shell script that monitors whether the file has been modified
# watchfile.sh
#! / bin / bash

TT = 5 # 5 seconds
NFILE = $ 1 #the watched file

#origin length of the file
len = `wc -l $ NFILE | awk‘ {print $ 1} ’`

echo "$ NFILE has $ len lines"

while:
do
   if [-N $ NFILE]
   then
   echo "` date`: new entry in $ NFILE "
   newlen = `wc -l $ NFILE | awk‘ {print $ 1} ’`
   newlines = `expr $ newlen-$ len`
   tail-$ newlines $ NFILE
   len = $ newlen
   fi
   sleep $ TT
done

6 test procedures for regular expressions

# RE.sh
#! / bin / bash

for deb in / root / shell / *
do
pkgname = `basename $ deb`
if [[$ pkgname = ~. * \. deb]]; then
#Reminder if followed by [with space, there is a space in front of $, and a space after deb
   echo "FILE $ pkgname is a debian package"
else
   echo "File $ pkgname is not a debian package"
fi
done

Another addition to the captured

#How to capture the string in parentheses
#Save in BASH_REMATCH [] array
# RE1.sh
#! / bin / bash
# manage to know your name
read -p "please input your fullname:" NAME
if [[$ NAME = ~ (. *) [[: space:]] (. *)]]; then
echo "Your last name $ {BASH_REMATCH [2]}"
echo "You're called $ {BASH_REMATCH [1]}"
echo "full name $ {BASH_REMATCH [0]}"
fi
Results of the
[[email protected] shell] # ./RE1.sh
please input your fullname: liancao liu
Your surname liu
Your name is liancao
Full name liancao liu

71 scripts to guess numbers

#A guess the number of sh
# numguess.sh
#! / bin / bash
#you may want to guess between 0-50
WORDS = 51
GUESS = -1
TIME = 0
BELOW = 0
TOP = `expr $ WORDS-1`
let ANSWER = ($ RANDOM% $ WORDS)
let ANSWER + =-1

while ["$ GUESS" -ne "$ ANSWER"]
do
echo "the number is between $ BELOW and $ TOP"
         read -p "your guess:" GUESS
let TIME + = 1
if ["$ GUESS" -lt "$ ANSWER"]; then
         echo "please input larger"
BELOW = `expr $ GUESS + 1`
elif ["$ GUESS" -gt "$ ANSWER"]; then
echo "please input smaller"
TOP = `expr $ GUESS-1`
else
         echo "right! you guessed $ TIME times"
         fi
done 

This article is from the "Learning Path of Kai Learning" blog, please make sure to keep this source http://qixue.blog.51cto.com/7213178/1654508

Shell Learning Condition test (refer to Shell scripting tricks)