memory leak

leak-bash-4.3.sh

#!/bin/bash

# Memory leak induced by the idiom "cmd | read var"
# but not by "read var < <(cmd)"
# Fixed in bash 4.4

# use strict
set -u
# Also fails with no monitor + lastpipe
#set +m
#shopt -s lastpipe

typeset -i i=0
typeset -i max=10000

function getrss { grep VmRSS /proc/$$/status; }
function getdata { echo 1 2 3 4 5; }

typeset rss_start="$(getrss)"
echo "Before loop: RSS = $rss_start"

while [[ $i -lt $max ]]; do

	typeset rss_curr="$(getrss)"
	[[ "$rss_start" != "$rss_curr" ]] && {
		echo "New mem usage at loop $i: $rss_start => $rss_curr"
		rss_start=$rss_curr
	}

	# First half, let's try the working method
	if [[ $i -lt $(( $max/2 )) ]]; then
		# That bashism is fine
		read some data < <(getdata)
	else
		# That one leaks something
		getdata | read some data
	fi

	i=i+1
done