Find the biggest number from a file by bash

Question

I would like to find the biggest value from the file, and the file is as below:

my code is as below(max.sh):

#!/usr/bin/bash

max=1
cat ./num | while read line; do
    if [ $line -gt $max ]; then
        max=$line
    fi
done
echo $max

but when I bash -x max.sh, the output is:

+ max=1
+ cat ./num
+ read line
+ '[' 1 -gt 1 ']'
+ read line
+ '[' 2 -gt 1 ']'
+ max=2
+ read line
+ '[' 3 -gt 2 ']'
+ max=3
+ read line
+ '[' 1 -gt 3 ']'
+ read line
+ '[' 2 -gt 3 ']'
+ read line
+ '[' 3 -gt 3 ']'
+ read line
+ '[' 4 -gt 3 ']'
+ max=4
+ read line
+ '[' 5 -gt 4 ']'
+ max=5
+ read line
+ '[' 1 -gt 5 ']'
+ read line
+ '[' 2 -gt 5 ']'
+ read line
+ '[' 3 -gt 5 ']'
+ read line
+ echo 1
1

it looks the max get the biggest value, but why the last echo of max is 1?

BTW, here are [`awk` one-liners](https://unix.stackexchange.com/q/170204/46316) for a similar task. — Ken Y-N, Oct 25 '17 at 04:51
`sort -nr num | head -n1` is looks easier to understand, adopted. — Bright Zhao, Oct 25 '17 at 06:14

anubhava · Accepted Answer · 2017-10-25T08:00:03.427

3

You are getting value of 1 because you are using an unnecessary pipeline which is making while loop executing in a sub-shell hence value of max getting lost in child shell itself and you get preset value of 1 in parent shell after loop.

It is better to use awk for this:

awk 'min == "" || $1<min{min=$1} $1>max{max=$1} END{print min, max}' file

5

edited Oct 25 '17 at 08:00

answered Oct 25 '17 at 04:51

anubhava

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can you explain a little bit about the above? – Bright Zhao Oct 25 '17 at 05:30
It is pretty simple `awk`. For each record, It compares a variable `max` with `$1` and when we find `$1` greater than `max` then we reset `max` to `$1` again. – anubhava Oct 25 '17 at 05:35
I suggest reading [awk guide](https://www.gnu.org/s/gawk/manual/gawk.pdf) or a good tutorial. – anubhava Oct 25 '17 at 05:38
if I wish to find out the smallest num, what the awk looks like? – Bright Zhao Oct 25 '17 at 06:07
1

See my updated answer for finding min and max – anubhava Oct 25 '17 at 08:01

Find the biggest number from a file by bash

1 Answers1