"let" command is not found in my bash script

Question

I have the following bash script,

#!/bin/bash
echo $SHELL

i=1
for img in ../img/*.png; do
  echo $img
  new=$(printf "../img/tmp/pyr%d.png" "$i")
  echo $new
  # cp "$img" "$new"
  let i=i+1
done
# avconv -r 2  -i ../img/tmp/pyr%d.png -b:v 1000k ../pop_pyr.mp4

In the ../img folder, there are files pyr1920.png, pyr1925.png, ...

When I run this script, I get this error

../img/pyr1920.png
../img/tmp/pyr1.png
make_video.sh: 10: make_video.sh: let: not found
../img/pyr1925.png
../img/tmp/pyr1.png

But I pasted the script in a terminal, it works perfectly fine.

../img/pyr1920.png
../img/tmp/pyr1.png
../img/pyr1925.png
../img/tmp/pyr2.png

My environment it ubuntu 14.04. I understand that default /bin/sh is dash. I make sure to use bash and check by echo $SHELL.

Why it doesn't work as a script but works fine from a terminal? I tried to find a solution but all I can find is about "dash" and "bash" setting.

That's not a bash error message; you aren't running your script with bash. — chepner
– chepner, Commented Feb 22, 2017 at 13:52
@chepner, Yes, now I realized it works with "bash myscript.sh". Doesn't it run bash if I write "#!/bin/bash" on the top of the script? — user26767
– user26767, Commented Feb 22, 2017 at 13:57
It should; how are you running it? Incidentally, $SHELL does not contain the name of the current shell; it's the name of your default shell. — chepner
– chepner, Commented Feb 22, 2017 at 14:00
Even my default shell is /bin/bash, I checked just open a terminal and type $SHELL. I am confused. — user26767
– user26767, Commented Feb 22, 2017 at 14:07

Kent · Accepted Answer · 2017-02-22 13:45:31Z

16

do in this way:

i=$((i+1))

or

i=$(expr $i + 1)

answered Feb 22, 2017 at 13:45

Kent

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1 Comment

chepner Over a year ago

If $((...)) doesn't work, there's no reason to believe expr is available either.

user26767 · Accepted Answer · 2017-02-22 14:03:52Z

7

I am sorry for answering my question. I was running my script with sh script.sh not bash script.sh. bash script.sh worked fine.

But isn't that I can specify it by #!/bin/bash on the top of a script?

answered Feb 22, 2017 at 14:03

user26767

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4 Comments

chepner Over a year ago

If you run the script by passing its name as an argument to a specific interpreter (like sh), the shebang is ignored. It is only used when you make the script executable and run it directly (chmod +x script.sh; ./script.sh)

user26767 Over a year ago

Thank you very much for the comment! It explained clearly and saved me a lot of time. I was stucked in this for long time.

cdarke Over a year ago

@user26767: please accept an answer to prevent others spending time on this.

Daniel Griscom Over a year ago

BTW, adding (and accepting if you like) your own answer is NOT a bad thing. We're working to accumulate knowledge, and that's part of the process.

jhonxito · Accepted Answer · 2018-11-19 23:28:27Z

0

I also had the same error, checking I found that with this code you get what you need

i=`expr $i + 1`

answered Nov 19, 2018 at 23:28

jhonxito

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