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.
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
x=$(($x + 1))...or variants on that theme, including : $((x++))...I agree: built-in arithmetic would be better, but the bc code can be made to work too.
exprESC key, <backquotes> not 'x is not getting initialized....before the while, add x=0 or whatever initialization you want. Please see my answer, I added some examples for you. Also note that expr $x +1 is WRONG, it has to be expr $x + 1 (note the space before 1)You seem to have a parse error. You need a backquote. Change line to:
x=`echo "$x + 1" | bc`
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
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).
letfor arithmetic operations i.e.while [ $x -lt 10 ]; do echo $x; let x=x+1; done(( ))instead of let.