Calculations in the shell

Numerical calculation of variables in shell common commands

(()), let, expr, BC, $[]

One, (())

Example:

[[Email Protected]hell ~]# echo $ ((1+2)) 3

Second, let

Example:

[[email protected] ~]# let a=1+2 [[email protected] ~]# echo $a 3

Third, expr

Example:

1.

[Email protected] ~]# expr 1+2 1+2

[[email protected] ~]# Expr 1 + 2 3

2.

[[email protected] ~]# Expr 2 \* 2 4

3.

[[email protected] ~]# expr $[2+3] 5

Special usage:

To determine the file extension example:

    [[email protected] ~]# vim  ' which ssh-copy-id  '      #  Judge file extensions     # check if we have 2  parameters left, if so the first is the new id file     if [ -n  "$"  ]; then      if          xpr  "$"  :  ". *\.pub" > /dev/null ;  then          id_file= "$"        else          id_file= "$1.pub"        fi        shift          # and this should leave $1 as the target name     fi

         determines whether an integer or non-integer input is an example:

    [[email protected] script]# cat expr.sh      #!/bin/bash    while true    do         read -p  "PLS INPUT :"  a         expr  $a  + 0 > /dev/null 2>&1         [ $? -eq 0 ] && echo int | |  echo chars    done    [[email protected] script]#  sh expr.sh     Pls input :2    int     pls input :3    int    pls input  :a    chars    Pls input :i     chars    pls input : >    chars    pls input : 

Example of determining the length of a character:

[Email protected] script]# chars= ' seq-s "[[email protected] script]# echo ${#chars} 291 [[Email Protect ED] script]# echo $ (expr length "$chars") 291

Four, BC

    ##  General Calculation     [[EMAIL PROTECTED] SCRIPT]# BC     bc 1.06.95    copyright 1991-1994, 1997, 1998,  2000, 2004, 2006 Free Software Foundation, Inc.     this is free software with absolutely no warranty.     for details type  ' warranty ' .     1+2    3     1.3+2    3.3    2*3    6     ^C     (interrupt)  Exiting bc.    ##  On the command line Operations     [[email protected] script]# echo 1+1|bc     2     #进制转换     [[email protected] script]# echo   "obase=2;82" |bc    1010010 

Special Examples:

[[email protected] script]# echo ' seq-s ' + ' + ' = ' seq-s ' + ' |BC ' 1+2+3+4+5+6+7+8+9+10=55

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Calculations in the shell