Arithmetic comparison operator using if inside a for loop in Bash

Question

I am trying to run the below logic in a bash script

  for i in {1..30}:
  do
  printf $i 
  if (( $i!=30 )); then
    printf ","
  fi
  done

After hours of google searching, I found that in an if condition, square brackets [ ] are used for string comparisons and circular brackets are used for arithmetic operations (( )). I also found that -ne is used for string and != has to be used for arithmetic operations.

Inspite of my best efforts, I am unable to successfully run this simple logic where I need to run the loop 30 times and print the output with commas but skip the comma in last iteration.

You mean like this? for i in {1..30}; do printf $i ; if [ "$i" != "30" ]; then printf ","; fi; done — Hackerman
– Hackerman, Commented Nov 16, 2018 at 20:24
-ne etc are not used for string comparisons. Inside [ ] or [[ ]], you use -eq, -ne, etc for numeric comparisons and = (note: just one equal sign, although bash allows two), !=, etc for string comparisons. In arithmetic contexts like (( )), you use == (note: double-equal), !=, etc for numeric comparisons, = for assignment, and there are no string operators. In other words: the operators change completely depending on context. — Gordon Davisson
– Gordon Davisson, Commented Nov 16, 2018 at 23:45

HugoTeixeira · Accepted Answer · 2018-11-16 20:27:59Z

1

You can simply remove the colon : after the curly braces in the first line:

for i in {1..30}
do
  printf $i 
  if (( $i!=30 )); then
    printf ","
  fi
done

This prints what you want:

1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30

answered Nov 16, 2018 at 20:27

HugoTeixeira

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2 Comments

ilegolas Over a year ago

Thanks. some of the examples I saw used colon for a for loop so I used it.

chepner Over a year ago

Were you looking at Python examples? I can't imagine why any shell examples would use a colon. (Or did you really see a semicolon (;)? One would be required if do were on the same line as for, but would be optional otherwise.)

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