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Shell Programming and Scripting

Looking to optimize code

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# 1  
Old 12-26-2015
Hammer & Screwdriver Looking to optimize code
Hi guys,

I feel a bit comfortable now doing bash scripting but I am worried that the way I do it is not optimized and I can do much better as to how I code.

e.g.

I have a whole line in a file from which I want to extract some values.

Right now what I am doing is :
Code:
STATE=`cat /opt/scripts/start.log | awk '{print $3}'`
TIME=`cat /opt/scripts/start.log | awk '{print $2}' | cut -d, -f1 `
DATE=`cat /opt/scripts/start.log | awk '{print $1}'`

echo " The app started at $STATE $TIME with state $STATE."

Is this a good way to extract 3 words (strings) from a line of text ? Or is there a better/more optimized way of doing this ?
# 2  
Old 12-26-2015
At least you can avoid the execution of cat; awk can directly read the file.
It is a bit strange that your file seems to be a log file - what happens if it has more than one line?
The following efficient shell builtin reads one line into three variables
Code:
read DATE TIME STATE  < /opt/scripts/start.log

Might need some little post processing...
Last edited by MadeInGermany; 12-26-2015 at 03:19 PM.. Reason: changed order
# 3  
Old 12-26-2015
And the post processing MadeInGermany mentioned would be something like:
Code:
TIME=${TIME%%,*}

followed by the echo you already had.
# 4  
Old 12-26-2015
And that post processing that Don used is an example of what you can do with Parameter Substitution. There are many other ways you can carve a piece of information out of a string, without the need of invoking an external program, which it will always be slower that using the built-in shell functionalities.
# 5  
Old 12-26-2015
Finally: you won't need the subshell execution any more utilizing the advice you already got, but for future reference, in the cases where you do need it: the backticks should not be used any more! They are a leftover from the original Bourne shell, which is outdated by some 25 years now. Use the modern POSIX way of process substitution:

Code:
variable=`command1 | command2`     # old, do not use!
variable=$(command1 | command2)    # the modern way to do the same

I hope this helps.

bakunin
# 6  
Old 12-27-2015
And, as there may be more than those three strings in a line, you might want to provide for a "sag wagon" for the trailing rest:
Code:
read DATE TIME STATE REST < /opt/scripts/start.log

This User Gave Thanks to RudiC For This Post:
MadeInGermany
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