The main bash version targeted is the 3.x line and generally won't work in older versions.

• vcs version 1.0.11 included patches to run on bash 2.x but never really worked
• vcs version 1.11 and 1.12 work on bash 2.05b and higher, 1.12.2 will be the last version capable of doing so, newer versions will require bash 3.1

References: http://wiki.bash-hackers.org/scripting/bashchanges

• for ((;;)): C-style for. Loops in bash are *really* slow, an inline AWK loop, is much faster
• [[ ... ]]: test replacement. Builtin with cleaner syntax and parsing, no need to quote, grouping (parentheses), && and || instead of -a and -o, arithmetic operators (e.g. -eq) force arithmetic evaluation (i.e. [[ 2 -eq "1+1" ]] is true):
  [ “$VAR” = “$X” -a 2 -eq $(( 1+1 )) ] → [[ $VAR = $X && 2 -eq '1+1' ]]
  Pitfall: When unquoted, the right hand side of a text comparison ('=', '==' and '!=') is considered a pattern ^{1) 2)}

• caller: caller 0 prints the calling function and line
• [[ =~ ]]: Pattern matching (right side can be an extended regular expression) ³⁾
  Pitfalls: when quoted, it isn't considered an ERE in bash 3.2 and up, but it is in bash 3.1. A variable can be used to get the same behaviour or the shell settings shopt compat31 / shopt compat32 be used.