Mimicking the Python "for-else" construct

Question

Python has a handy language feature called "for-else" (similarly, "while-else"), which looks like this:

for obj in my_list:
    if obj == target:
        break
else: # note: this else is attached to the for, not the if
    print "nothing matched", target, "in the list"

Essentially, the else is skipped if the loop breaks, but runs if the loop exited via a condition failure (for while) or the end of iteration (for for).

Is there a way to do this in bash? The closest I can think of is to use a flag variable:

flag=false
for i in x y z; do
    if [ condition $i ]; then
        flag=true
        break
    fi
done
if ! $flag; then
    echo "nothing in the list fulfilled the condition"
fi

which is rather more verbose.

Answer 1

Using a subshell:

( for i in x y z; do
    [ condition $i ] && echo "Condition $i true" && exit;
done ) && echo "Found a match" || echo "Didn't find a match"

Answer 2

You could put a sentinel value in the loop list:

for i in x y z 'end-of-loop'; do
    if [ condition $i ]; then
        # loop code goes here
        break
    fi
    if [ $i == 'end-of-loop' ]; then
        # your else code goes here
    fi
done

Answer 3

Something very hacky to introduce similar syntax:

#!/bin/bash

shopt -s expand_aliases

alias for='_broken=0; for'
alias break='{ _broken=1; break; }'
alias forelse='done; while ((_broken==0)); do _broken=1;'

for x in a b c; do
        [ "$x" = "$1" ] && break
forelse
        echo "nothing matched"
done

 

$ ./t.sh a
$ ./t.sh d
nothing matched

Answer 4

You can do this but I personally find it hard to read:

while :;
  do for i in x y z; do
    if [[ condition ]]; then
      # do something
      break 2
  done
  echo Nothing matched the condition
  break
done

Answer 5

You can change this

if ! $flag; then
    echo "nothing in the list fulfilled the condition"
fi

to something simpler like this

"$flag" || echo "nothing in the list fulfilled the condition"

if you only have one statement after it, although that's not really going to help much.

Answer 6

I also enjoy devnull's answer, but this is even more pythonic:

for i in x y z; do
  [ condition $i ] && break #and do stuff prior to break maybe?
done || echo "nothing matched"

This will only echo "nothing matched" if the loop did not break.