CODEWITHSUNDEEP
unix
Bit_hunter
Bit_hunter

Reputation: 809

Error in while loop in bash shell

I am beginner in UNIX. I am getting a silly error while writing a while loop.

Code:-

$ x=0
$ while [ $x -lt 10 ]
> do
> echo $x
> x=´echo "$x + 1" | bc´
> done;

I am getting the errors:-

0
bc´: command not found   
0
bc´: command not found
0
bc´: command not found
...

Can any body help me? I have no idea of shell programming.

Upvotes: 0

Views: 1836

Answers (4)

Tim Pote
Tim Pote

Reputation: 28029

You're not using backticks. Use ` (aka grave accent, aka U+0060) (found in the top-left on American keyboards) instead of ´ (aka acute accent, aka U+00B4).

For example, the following works fine:

x=0
while [ $x -lt 10 ]; do
  echo $x
  x=`echo "$x + 1" | bc`
done

The only difference between yours and mine are the ticks used to quote echo "$x + 1" | bc.

That being said, if you happen to be using bash (or a bash-like shell), there are much better ways of making the same loop. For example:

x=0
while (( x++ < 10  )); do
  echo $x
done

This has the advantage of being both faster (because it doesn't call to outside programs) and easier to read (because it uses more traditional coding syntax).

Upvotes: 0

Bill
Bill

Reputation: 5772

If you are doing x=´echo "$x + 1" | bc´ to increment x (which is wrong as pointed by danf), pls use the following 

x=`expr $x + 1`

also note the spaces...bash is very picky

Here is the output --

xxxx@cse:~> x=5
xxxxx@cse:~> while [ $x -lt 10 ]; do echo $x; x=`expr $x + 1`; done;
5
6
7
8
9

You can use bc to get this to work, but it is better to use expr

xxxx@cse:~> x=5
xxxx@cse:~> while [ $x -lt 10 ]; do echo $x; x=`echo "$x + 1"|bc`; done;
5
6
7
8
9

Upvotes: 1

user594138
user594138

Reputation:

Don't use backticks to execute subcommands, use $( cmd ), this construct can be nested. Maybe you do the arithmetic with a pipe to bc for learning purposes, otherwise, the shell is capable of doing this in a number of ways 

$((x+=1))
x=$((x+1))
$((++x))
$((x++))

HTH and kind regards

Upvotes: 0

dan
dan

Reputation: 1002

You seem to have a parse error. You need a backquote. Change line to:

x=`echo "$x + 1" | bc`

Upvotes: 0

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