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How to read file line by line in shell script?

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# 1  
Old 03-01-2020
How to read file line by line in shell script?

Hi Team,

I want to read a file line by line and print the data in multiple variables.

By using below script i am doing that but i want to increase the performance by using for loop Can someone let me know how to do that ?.

Below is my script:

ps aux  > /tmp/test
sed 1d  /tmp/test >  /tmp/test1

while IFS= read -r line;

USER=$(echo "$line"|awk  '{print $1}')

CPU_percentage=$(echo "$line"|awk  '{print $3}')

echo -e "{\"'PID'\":\"'"$PID"'\",\"'CPU_percentage'\":\"'"$CPU_percentage"'\"}"

done < /tmp/test1

How to use for loop for above script to get more performance from the shell script ?.

Moderator's Comments:
Mod Comment Please use code tags ext time, for your code and data, Thanks

Last edited by vbe; 03-01-2020 at 08:25 PM..
# 2  
Old 03-01-2020
Instead of reading the input a line at a time:
read a
while read a b c d e f
    echo USER= $a CPU= $c

run as

ps aux |script_above

You end up only reading the output of ps once instead of multiple times.
# 3  
Old 03-01-2020
Following along from jgt's suggestion you could try this all in one script:

ps aux | (
   # discard first (headings) line
   read a

   while read a b c rest
       echo -e "{\"'PID'\":\"'"$a"'\",\"'CPU_percentage'\":\"'"$c"'\"}"

# 4  
Old 03-02-2020
Try this
ps --no-headers -eo "{\"'PID'\":\"'%p'\",\"'CPU_percentage'\":\"'%C'\"}"

and so on if you need add fields

Last edited by nezabudka; 03-02-2020 at 03:02 AM..
This User Gave Thanks to nezabudka For This Post:

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