linux command

expr

Linux Command – expr ใช้ประมวลผลตรรกะคณิตศาสตร์

 

คำสั่ง

1. Boolean expression

$ expr 3 = 3
1

$ expr 3 \> 3
0

 

2. Mathematic expression

$ expr 20 + 23
43

$ expr 20 - 23
-3

$ expr 20 \* 23
460

$ expr 20 / 23
0

 

 

โครงสร้างคำสั่ง

 expr EXPRESSION
 expr OPTION

 

รายละเอียด

เป็นคำสั่งที่ใช้ประมวลผลตรรกะคณิตศาสตร์ คล้ายเงือนไขที่อยู่ใน if statement เช่นสำหรับ boolean

  • True = 1
  • False = 2

 

Option

 --help display this help and exit

 --version
 output version information and exit

 Print the value of EXPRESSION to standard output. A blank line below separates increasing precedence groups. EXPRESSION may be:

 ARG1 | ARG2
 ARG1 if it is neither null nor 0, otherwise ARG2

 ARG1 & ARG2
 ARG1 if neither argument is null or 0, otherwise 0

 ARG1 < ARG2
 ARG1 is less than ARG2

 ARG1 <= ARG2
 ARG1 is less than or equal to ARG2

 ARG1 = ARG2
 ARG1 is equal to ARG2

 ARG1 != ARG2
 ARG1 is unequal to ARG2

 ARG1 >= ARG2
 ARG1 is greater than or equal to ARG2

 ARG1 > ARG2
 ARG1 is greater than ARG2

 ARG1 + ARG2
 arithmetic sum of ARG1 and ARG2

 ARG1 - ARG2
 arithmetic difference of ARG1 and ARG2

 ARG1 * ARG2
 arithmetic product of ARG1 and ARG2

 ARG1 / ARG2
 arithmetic quotient of ARG1 divided by ARG2

 ARG1 % ARG2
 arithmetic remainder of ARG1 divided by ARG2

 STRING : REGEXP
 anchored pattern match of REGEXP in STRING

 match STRING REGEXP
 same as STRING : REGEXP

 substr STRING POS LENGTH
 substring of STRING, POS counted from 1

 index STRING CHARS
 index in STRING where any CHARS is found, or 0

 length STRING
 length of STRING

 + TOKEN
 interpret TOKEN as a string, even if it is a

 keyword like 'match' or an operator like '/'

 ( EXPRESSION )
 value of EXPRESSION

 Beware that many operators need to be escaped or quoted for shells. Comparisons are arithmetic if both ARGs are numbers, else lexicographical. Pattern matches return the string
 matched between \( and \) or null; if \( and \) are not used, they return the number of characters matched or 0.

 

กลุ่มคำสั่ง

 

Reference:

คำสั่ง Unix – Linux Command

Linux, Unix

 

Author: Suphakit Annoppornchai

Credit: https://saixiii.com

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