Insert text before the first non-comment-line before a pattern - awk

Question

To update a system configuration file on a Linux server I was in need to add a rule (line of text) before a given other rule (and, if possible, before the comments of that other rule).
With the following input file:
# Foo
# Bar
# Comment about rule on the next line
RULE_A
# Comment about rule on the next line
# Continuation of comment
RULE_B
I want to get the following output:
# Foo
# Bar
# Comment about rule on the next line
RULE_A
# ADDED COMMENT
# ADDED COMMENT CONTINUATION
ADDED_RULE
# Comment about rule on the next line
# Continuation of comment
RULE_B
I ended up with the following combination of :
sed : convert my multi-line text to add in a single line with \n.
tac : to reverse the file.
awk : to work on the file.
A temporary file that will replace the original file (because I don't have "in-place" option on awk)
CONF_FILEPATH="sample.conf"
# Create sample work file:
cat > "${CONF_FILEPATH}" <<EOT
# Foo
# Bar
# Comment about rule on the next line
RULE_1
# Comment about rule on the next line
# Continuation of comment
RULE_2
RULE_3_WITHOUT_COMMENT
RULE_4_WITHOUT_COMMENT
RULE_5_WITHOUT_COMMENT
# Comment about rule on the next line
RULE_6
# Comment about rule on the next line
# Continuation of comment
RULE_7
EOT
# Text (of new rule) to add:
TEXT_TO_ADD="# ADDED COMMENT
# ADDED COMMENT CONTINUATION
ADDED_RULE
"
# The rule before which we want to add our text:
BEFORE_RULE="RULE_7"
# Temporary file:
TMP_FILEPATH="$(mktemp)"
# Convert newlines to \n:
TEXT_TO_ADD_FOR_AWK="$(echo ${TEXT_TO_ADD} | tac | sed -E ':a;N;$!ba;s/\r{0,1}\n/\\n/g')"
# Process
awk 'BEGIN {
ADD_TO_LINE="";
}
{
if ($0 ~ "^'${BEFORE_RULE}'") {
# DEBUG: Got the "deny all" line
ADD_TO_LINE=NR+1 ;
print $0;
} else {
if (ADD_TO_LINE==NR) {
# DEBUG: Current line is the candidate
if ($0 ~ "#") {
ADD_TO_LINE=NR+1;
# DEBUG: Its a comment, wont add here, taking note to try on the next line
print $0;
} else {
# DEBUG: Not a comment: this is the place!
print "'${TEXT_TO_ADD_FOR_AWK}'";
ADD_TO_LINE="";
print $0;
}
} else {
print $0;
}
}
}' <(tac "${CONF_FILEPATH}") \
| tac > "${TMP_FILEPATH}"
# Overwrite:
cat "${TMP_FILEPATH}" > "${CONF_FILEPATH}"
# Cleaning up:
rm "${TMP_FILEPATH}"
I then get (look just before RULE_7):
# Foo
# Bar
# Comment about rule on the next line
RULE_1
# Comment about rule on the next line
# Continuation of comment
RULE_2
RULE_3_WITHOUT_COMMENT
RULE_4_WITHOUT_COMMENT
RULE_5_WITHOUT_COMMENT
# Comment about rule on the next line
RULE_6
# ADDED COMMENT
# ADDED COMMENT CONTINUATION
ADDED_RULE
# Comment about rule on the next line
# Continuation of comment
RULE_7
Which is OK, but I'm sure there is a cleaner/simpler way of doing that with awk.
Context: I am editing the /etc/security/access.conf to add an allow rule before the deny all rule.

Answer 1

Reading the file paragraph-wise makes things simpler:
awk -v text_to_add="$TEXT_TO_ADD" \
-v before_rule="$BEFORE_RULE" \
-v RS='' \
-v ORS='\n\n' \
'$0 ~ "\n" before_rule {print text_to_add} 1' file
Get out of the habit of using ALLCAPS variable names, leave those as
reserved by the shell. One day you'll write PATH=something and then
wonder why
your script is broken.

Answer 2

You never need sed when you're using awk:
text_to_add='# ADDED COMMENT
# ADDED COMMENT CONTINUATION
ADDED_RULE
'
before_rule='RULE_B'
awk -v rule="$before_rule" -v text="$text_to_add" '
/^#/ { cmt = cmt $0 ORS; next }
$0==rule { print text }
{ printf "%s%s\n", cmt, $0; cmt="" }
' file
# Foo
# Bar
# Comment about rule on the next line
RULE_A
# ADDED COMMENT
# ADDED COMMENT CONTINUATION
ADDED_RULE
# Comment about rule on the next line
# Continuation of comment
RULE_B
If you can have comments after the final non-comment line then just add END { printf "%s", cmt } to the end of the script.
Don't use all-caps variable names (see Correct Bash and shell script variable capitalization) and always quote shell variables (see https://mywiki.wooledge.org/Quotes). Copy/paste your original script into http://shellcheck.net and it'll tell you some of the issues.
Regarding ...because I don't have "in-place" option on awk from your question - GNU awk has -i inplace for that.

Answer 3

ed, the standard editor, to the rescue! Because it looks at the entire file, not just a line at a time, it's able to move the current line cursor around forwards and backwards with ease:
ed -s input.txt <<EOF
/RULE_7/;?^[^#]?a
# ADDED COMMENT
# ADDED COMMENT CONTINUATION
ADDED_RULE
.
w
EOF
After this, input.txt looks like your desired result.
It first sets the current line to the first one containing RULE_7, then looks backwards for the first non-empty line above it that doesn't start with # (The line with RULE_6 in this case), and appends the desired text after that line. Then it writes the modified file back to disk.