Increment variable value by 1 ( shell programming)

问题

I am a beginner to shell programming and it sounds like a very stupid question but i cant seem to be able to increase the variable value by 1. I have looked at tutorial but it only shows how to add together 2 variables

I have tried the following methods but it doesnt work

i=0

$i=$i+1 # doesnt work , command not found

echo "$i"

$i='expr $i+1' # doesnt work , command not found

echo "$i"

$i++ # doesnt work , command not found

echo "$i"

How do i increment the value of a variable by 1??

回答1:

You can try this :

i=0
i=$((i+1))

回答2:

There are more than one way to increment a variable in bash, but what you tried is not correct.

You can use for example arithmetic expansion:

i=$((i+1))

or only:

((i=i+1))

or:

((i+=1))

or even:

((i++))

Or you can use let:

let "i=i+1"

or only:

let "i+=1"

or even:

let "i++"

See also: http://tldp.org/LDP/abs/html/dblparens.html.

回答3:

The way to use expr:

i=0
i=`expr $i + 1`

the way to use i++

((i++)); echo $i;

Tested in gnu bash

回答4:

These are the methods I know:

ichramm@NOTPARALLEL ~$ i=10; echo $i;
10
ichramm@NOTPARALLEL ~$ ((i+=1)); echo $i;
11
ichramm@NOTPARALLEL ~$ ((i=i+1)); echo $i;
12
ichramm@NOTPARALLEL ~$ i=`expr $i + 1`; echo $i;
13

Note the spaces in the last example, also note that's the only one that uses $i.