Bash file while loop isnt running well
I am using the Ubuntu terminal emulator for Windows 10 to try learn the Linux terminal.
I have this code:
cat > c1.sh
echo Give me your name!
read name
echo How many times do you want your laptop to print out your name?
read numberOfLoops
i=0
while [ $i -lt $numberOfLoops ]
do
echo $name
i=$i+1
done
#end
I create the executable file and begin running it:
./c1.sh
Give me your name!
Root
How many times do you want your laptop to print out your name?
3
Root
./c1.sh: line 6: [: 0+1: integer expression expected
It prints out the name Root "once" as it should but then it stops running and prints out the message ./c1.sh: line 6: [: 0+1: integer expression expected. However if there was a issue with the while loop then it wouldn’t print out the first time Root but it does so I’m not sure what is going on here.
This is not numeric addition:
i=$i+1
It’s string concatenation. If $i is 0, after the assignment it’s 0+1.
This is numeric addition in bash:
((i=i+1))
or shorter
((++i))
Although syntactically valid, the expression i=$i+1 is a string assignment, so that the second time through the loop you are comparing literal string 0+1 to an integer $numberOfLoops
To get arithmetic evaluation, you can use let i=$i+1, i=$((i+1)) or (in bash – for which you should add a #!/bin/bash shebang at the top of your script, ((i=i+1)) or even ((i++))
If you are really using bash (rather than sh) it would probably be more idiomatic to use a C-style for loop:
#!/bin/bash
read -r -p 'Give me your name! ' name
read -r -p 'How many times do you want your laptop to print out your name? ' numberOfLoops
for ((i=0; i<numberOfLoops; i++)); do
printf '%sn' "$name"
done
See also the Arithmetic Evaluation section of the bash manual.