How to resolve the error in bash script to put load on cpu?

Question

I have two scripts to put a spike on CPU .

infinite_loop.bash :

#!/bin/bash
while [ 1 ] ; do
    # Force some computation even if it is useless to actually work the CPU
    echo $((13**99)) 1>/dev/null 2>&1
done

cpu_spike.bash :

#!/bin/bash
# Either use environment variables for NUM_CPU and DURATION, or define them here
for i in `seq ${NUM_CPU}` : do
    # Put an infinite loop on each CPU
    infinite_loop.bash &
done

# Wait DURATION seconds then stop the loops and quit
sleep ${DURATION}
killall infinite_loop.bash

The script was earlier working fine. BUt now the scriptis not working fine. Its giving me an error :

./cpu_spike.bash: line 5: syntax error near unexpected token `infinite_loop.bash'
./cpu_spike.bash: line 5: `    infinite_loop.bash &'

Community · Accepted Answer · 2017-05-23 11:57:37Z

0

The error is in the following line:

for i in `seq ${NUM_CPU}` : do

You need to terminate the for using a ;, not :. Say:

for i in `seq ${NUM_CPU}` ; do

: is a null command.

Moreover, saying:

while [ 1 ] ; do command ; done

to simulate an infinite loop is incorrect while it actually does produce one. You might observe that saying:

while [ 0 ] ; do command ; done

would also result in an infinite loop. The correct way would be to say:

while true ; do command; done

or

while : ; do command; done

or

while ((1)); do command; done

For other variations of producing an infinite loop, see this answer.

edited May 23, 2017 at 11:57

CommunityBot

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answered Jan 10, 2014 at 11:09

devnull

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7 Comments

user3086014 Over a year ago

I just want to put a load on cpu using some script that goes in an infinite loop

user3086014 Over a year ago

Its giving me an error : seq: missing operand Try seq --help' for more information. ^C`

devnull Over a year ago

@user3086014 You would get this error if you haven't set the variable NUM_CPU.

devnull Over a year ago

@user3086014 Before any line using the variable NUM_CPU, set it to value. For example, saying NUM_CPU=4 would set the value to 4.

user3086014 Over a year ago

but earlier the script was working fine without setting the value for CPU

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