Shell learning: Shell echo, printf, test command, echotest

Shell learning: Shell echo, printf, test command, echotest
Shell learning: Shell echo, printf, test command Shell echo command

Show normal strings

echo "hello"

Output: hello

Double quotation marks can be omitted as follows:

echo hello

Output: hello

Show escape characters

Echo "\" hello \ "" or echo \ "hello \"

Output: "hello"

Show Variables

name="tom"echo "$name is a child"

Output: tom is a child

Display line feed

#-E: Enable escape echo-e "hello \ nworld"

Output:

helloworld

The display result is directed to the file.

echo "hello world" > myfile.txt

Run cat myfile.txt and Output

hello world

Display date

echo `date`

Output: Tue Jan 16 06:30:53 PST 2018.

Shell printf command

The Shell printf command imitates the printf () program in the C library.

Printf is defined by the POSIX standard. Therefore, it is better to use the printf script than echo for portability.

Syntax of printf:

printf format-string [arguments...]

Format-string: format control string arguments: list of parameters

Eg:

[Zhang @ localhost ~] $ Echo "hello, shell" hello, shell # if there is no line break, do not wrap [zhang @ localhost ~] $ Printf "hello world" hello world [zhang @ localhost ~] $ # Use the line break [zhang @ localhost ~] $ Printf "hello, shell \ n" hello, shell

Printf placeholder Function

Eg:

#!/bin/bashprintf "%-10s %-8s %-4s\n" name sex weightprintf "%-10s %-8s %-4.2f\n" zhangsan male 68.22printf "%-10s %-8s %-4.2f\n" lisi male 70.02printf "%-10s %-8s %-.2f\n" xiaolongnv female 48.12

Output:

name       sex      weightzhangsan   male     68.22lisi       male     70.02xiaolongnv female   48.12

Placeholders include % s, % d, % c, and % f.

%-10 s: the width is 10 characters.-indicates the left alignment, but not the right alignment. If not, spaces are automatically filled. Otherwise, all content is displayed.

%-4.2f: Indicates formatting decimal places, where. 2 indicates retaining two decimal places.

% D: format a number

Shell test command

The test command in Shell is used to check whether a condition is true. It can be used to test values, characters, and files.

Numerical Test

Parameters	Description
-Eq	Equal to true
-Ne	True if not equal
-Gt	True if the value is greater
-Ge	True if the value is greater than or equal
-Lt	True if the value is smaller
-Le	True if the value is less than or equal

Eg:

#!/bin/bashnum1=100num2=200if test $num1 -eq $num2then    echo "$num1 equal $num2"else    echo "$num1 not equal $num2"fi

Result:

100 not equal 200

String Testing

Parameters	Description
=	Equal to true
! =	True if not equal
-Z	If the string length is 0, it is true.
-N	If the string length is not 0, it is true.

Eg:

#!/bin/bashstr1="hello"str2="world"if test $str1 = $str2then    echo "$str1 equal $str2"else    echo "$str1 not equal $str2"fiif test -z $str1then    echo "$str1 is empty"else    echo "$str1 is not empty"fi

Output result:

hello not equal worldhello is not empty

File Test

Parameters	Description
-E	True if the file exists
-R	True if the object exists and is readable
-W	True if the file exists and can be written
-X	True if the file exists and is executable
-S	True if the file exists with at least one character
-D	True if the file exists and is a directory
-F	True if the object exists and is a file
-C	True if the object exists and is a special string File
-B	True if the object exists and is a special object

Eg:

Run the ls-l command in the user directory of zhang:

Run test-e Command:

[zhang@localhost ~]$ test -e 1.sh[zhang@localhost ~]$ if test -e 1.sh> then>     echo "1.sh file exist"> else>     echo "1.sh file not exist"> fi1.sh file exist

Run test-r Command:

[zhang@localhost ~]$ if test -r 1.sh> then>     echo "1.sh read ok"> else>     echo "1.sh read not ok"> fi1.sh read ok

Run test-x Command:

[zhang@localhost ~]$ if test -x myfile.txt> then >     echo "myfile.txt is execute file"> else>     echo "myfile.txt is not execute file"> fimyfile.txt is not execute file

Run test-d Command:

[zhang@localhost ~]$ if test -d test> then>     echo "test is a dir"> else>     echo "test is not a dir"> fitest is a dir

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