Bash script append variable to file

I just created bash script and want to append the variable script, but it was not working properly, and here is the script :

export PROMPT_COMMAND='RETRN_VAL=$?;logger -p local6.debug "$(whoami) [$$]: $(history 1 | sed "s/^[ ]*[0-9]\+[ ]*//" ) [$RETRN_VAL]"'

I tried to run append this script using echo but the results is not the same:

echo "export PROMPT_COMMAND='RETRN_VAL=$?;logger -p local6.debug "$(whoami) [$$]: $(history 1 | sed "s/^[ ]*[0-9]\+[ ]*//" ) [$RETRN_VAL]"'" > wew.txt

if we cat wew.txt the result was :

export PROMPT_COMMAND='RETRN_VAL=0;logger -p local6.debug widianto [69]: echo "export PROMPT_COMMAND='RETRN_VAL=$?;logger -p local6.debug "$(whoami) [$$]: $(history 1 | sed "s/^[ ]*[0-9]\+[ ]*//" ) [$RETRN_VAL]"'" > wew.txt []'

Thanks for your help

2 Answers

What you're observing here is that 'strong quotes' lose their strength when wrapped in "weak quotes":

$ echo $foo
bar
$ echo '$foo'
$foo
$ echo "echo '$foo'"
echo 'bar'

Although you could fix your code by backslash-escaping every special character, a better way to avoid expansion by the shell might be to use a here-document instead of an echo, and quote (in any of the supported ways - weak, strong or backslash) the end marker:

$ cat << \EOF
export PROMPT_COMMAND='RETRN_VAL=$?;logger -p local6.debug "$(whoami) [$$]: $(history 1 | sed "s/^[ ]*[0-9]\+[ ]*//" ) [$RETRN_VAL]"'
EOF
export PROMPT_COMMAND='RETRN_VAL=$?;logger -p local6.debug "$(whoami) [$$]: $(history 1 | sed "s/^[ ]*[0-9]\+[ ]*//" ) [$RETRN_VAL]"'

I have succesfully with created variable :

widianto@rancher3:~$ cat b.bash
#!/bin/bash
# widianto
a="export PROMPT_COMMAND='RETRN_VAL=$?;logger -p local6.debug"
b='"$(whoami) [$$]: $(history 1 | sed'
c='"s/^[ ]*[0-9]\+[ ]*//" ) [$RETRN_VAL]"'
echo "$a $b $c'" >> /home/widianto/test.txt

Thank you