CODEWITHSUNDEEP
bashwhile-loop
themightyscot
themightyscot

Reputation: 41

Bash while loop with done < $1

I'm a bit confused by the done < $1 notation.

I'm trying to write a program "sumnums" that reads in a file called "nums" that has a couple rows of numbers. Then it should print out the rows of the numbers followed by a sum of all the numbers.

Currently I have:

#!/bin/bash
sum=0;
while read myline
do  
  echo "Before for; Current line: \"$myline\""
done
for i in $myline; do  
  sum=$(expr $sum + $i)
done < $1    
echo "Total sum is: $sum"

and it outputs the list of the numbers from nums correctly then says ./sumnums: line 10: $1: ambiguous redirect, then outputs Total sum is: 0.

So somehow it isn't adding. How do I rearrange these lines to fix the program and get rid of the "ambiguous redirect"?

Upvotes: 3

Views: 12308

Answers (2)

Charles Duffy
Charles Duffy

Reputation: 295716

Assuming your filename is in $1 (that is, that your script was called with ./yourscript nums):

#!/bin/bash

[[ $1 ]] || set -- nums  ## use $1 if already set; otherwise, override with "nums"

sum=0
while read -r i; do      ## read from stdin (which is redirected by < for this loop)
  sum=$(( sum + i ))     ## ...treat what we read as a number, and add it to our sum
done <"$1"               ## with stdin reading from $1 for this loop
echo "Total sum is: $sum"

If $1 doesn't contain your filename, then use something that does contain your filename in its place, or just hardcode the actual filename itself.

Notes:

  • <"$1" is applied to a while read loop. This is essential, because read is (in this context) the command that actually consumes content from the file. It can make sense to redirect stdin to a for loop, but only if something inside that loop is reading from stdin.
  • $(( )) is modern POSIX sh arithmetic syntax. expr is legacy syntax; don't use it.

Upvotes: 4

karakfa
karakfa

Reputation: 67547

awk to the rescue! 

awk '{for(i=1;i<=NF;i++) sum+=$i} END{print "Total sum is: " sum}' file

bash is not the right tool for this task.

Upvotes: 0

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