shell只读变量删除

# readonly a=3.14
# a=2
-bash: a: readonly variable
# cat << EOF| gdb
> attach $$
> call unbind_variable("a")
> detach
> EOF
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-110.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
.
(gdb) Attaching to process 12409
Reading symbols from /usr/bin/bash...Reading symbols from /usr/bin/bash...(no 	debugging symbols found)...done.
(no debugging symbols found)...done.
Reading symbols from /lib64/libtinfo.so.5...Reading symbols from /lib64/libtinfo.so.5...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Loaded symbols for /lib64/libtinfo.so.5
Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnss_files.so.2
0x00007fd4b11db17c in waitpid () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install bash-4.2.46-30.el7.x86_64
(gdb) $1 = 0
(gdb) Detaching from program: /usr/bin/bash, process 12409
(gdb) quit

这时变量已经删除，可以重新赋值

# a=1
# echo $a
1