${varname//orig/replacement} construct really slow

[Steven Augart]

Configuration Information [Automatically generated, do not change]:
Machine: i386
OS: linux-gnu
Compiler: i386-redhat-linux-gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i386' 
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i386-redhat-linux-gnu' 
-DCONF_VENDOR='redhat' -DSHELL -DHAVE_CONFIG_H  -I.  -I. -I./include -I./lib 
-D_GNU_SOURCE  -O2 -g -pipe -march=i386 -mcpu=i686
uname output: Linux augart-tp23.watson.ibm.com 2.4.20-18.9 #1 Thu May 29 
07:08:16 EDT 2003 i686 i686 i386 GNU/Linux
Machine Type: i386-redhat-linux-gnu

Bash Version: 2.05b
Patch Level: 0
Release Status: release

Description:
        The ${varname//orig/replacement} construct is really slow; it takes
        741 milliseconds of CPU time (on a Pentium III, 1.1MHz) just
        to perform a simple string transformation; in this case, 
        turning 32 colon characters into spaces, in a variable with a
        608 character-long value.  

        (When I double the variable's length to 

Repeat-By:
        
  sh-2.05b$ time echo $foo
  
/bin:/usr/bin:/usr/local/bin:/home/augart/JikesRVM/Images/BaseBaseCopyMS+:/home/augart/JikesRVM/rvm/bin:/home/augart/JikesRVM/Configs:/opt/c4eb/bin:/opt/mts-client:/opt/IBMJava2-141/bin:/opt/Lotus/SameTime:/home/augart/.hosts:/home/augart/.bin:/home/augart/swa-startup/bash-lib:/usr/local/bin:/usr/local/sbin:/usr/local/mozilla:/sbin:/usr/sbin:/usr/bin:/bin:/usr/games:/usr/X11R6/bin:/usr/lib/java/bin:/home/augart/swa-startup:/home/augart/swa-startup/Oursite:/usr/local/etc:/home/augart/swa-startup/Oursite:/usr/local/etc:/home/augart/swa-startup/Oursite:/usr/local/etc:/opt/globus/bin:/opt/globus/sbin:/opt/c4eb/bin:/opt/IBMJava2-141/bin:/opt/c4eb/bin:/opt/IBMJava2-141/bin:/opt/c4eb/bin:/opt/IBMJava2-141/bin

  real  0m0.001s
  user  0m0.000s
  sys   0m0.000s
  sh-2.05b$ time echo ${foo//:/ } > /dev/null

  real  0m0.741s
  user  0m0.740s
  sys   0m0.000s
  sh-2.05b$ 

Here are some other timings that may be helpful in tracking down the
source of the problem.  (It goes up to 5872 milliseconds if I just
double the length of the variable):

  sh-2.05b$ foo=$foo$foo
  sh-2.05b$ time echo ${foo//:/ } > /dev/null

  real  0m5.872s
  user  0m5.820s
  sys   0m0.010s
  sh-2.05b$