Use $1 from .sh in regex pattern in order to replace content in a file

Question

I have been trying but without much success with capture a word between two words and Get Word Between two underscores among many many others...

I want to find the newline before "##", this "##' is after '## baba' but not right after, there is some text between. They are many "##" in the file, always preceded by \n. See below schema:

Desired output

##

## baba {could also be "foo" or "bar"}

rosa rosa rosam rosae ipsum

{append or replace the '\n' before '\n##' with -> helloworld here}


##

##

Once it is found insert "helloworld" given as an argument to the script

My current script find

awk -i inplace -v foo=$2 -v new=$1'\n\n' 'f&&/^##/{print new; f=0} {print} /^## baba/{f=1}' a.md

I want two things: 1/ to replace baba with argument $2 (variable foo), 2/ to include the \n in ^## to have it one line above.

Thank you very much for any help

---

Edit : Thanks to Rudic I came up with:

a.sh

sed -re "/## $1/,/^\n\n##/ {s/^## *$/$2\n\n\n&/}" a.md

a.md

##


## baba

rosa rosa rosam rosae ipsum



##



##

command line

cat a.md && echo "---------------" && ./test.sh baba remember140416sewol

But output has 2 flaws, 1/ write for each match, I want only the first match, 2/ does not replace the new line before the other newline:

##


## baba

rosa rosa rosam rosae ipsum

{\n <-extra new line}
remember140416sewol


##


remember140416sewol {<-- extra occurence}


##

Answer 1

Mayhap something along this line:

sed '/## *baba/,/^##/ {s/^## *$/helloworld\n&/}' file

or, if given as parameters,

sed "/## *$2/,/^##/ {s/^## *$/$1\n&/}" file

Answer 2

The following would take a pattern from the command line as well as a replacement text, and assign these to the awk variables pattern and text.

In the BEGIN block, I modify the pattern to include the regular expression ^##  at the start.

I then use a range expression to trigger a block of code that will execute for the given section in the document (the section starting with ##  followed by the thing that matches the original pattern, until the line that matches the expression ^##$).

If, within that block, the current line happens to match the expression ^##$, I print the hello world string given by the user, with two extra newlines added.

All lines of input are printed by the final { print } block.

If you want to use the positional parameters $1 (for the replacement text) and $2 (for the pattern), replace the baba below with $2 and hello world with $1. Likewise if you have any other two variables that holds the replacement text and pattern.

awk -v pattern="baba" -v text="hello world" '
    BEGIN { pattern = "^## " pattern }
    $0 ~ pattern,/^##$/ { if (/^##$/) print text "\n\n" }
    { print }' a.md

An alternative implementation that takes the pattern and text from two environment variables:

PATTERN="baba" TEXT="hello world" awk '
    BEGIN { pattern = "^## " ENVIRON["PATTERN"] }
    $0 ~ pattern,/^##$/ { if (/^##$/) print ENVIRON["TEXT"] "\n\n" }
    { print }' a.md

Given the document at the end of your question, this would generate

##

## baba

rosa rosa rosam rosae ipsum


hello world


##

##

Related to passing data by variables into awk:

• Do I need to encapsulate awk variables in quotes in order to sanitize them?

---

As requested in comments, a script that would take two arguments, a pattern and a replacement string, or the two environment variables PATTERN and STRING:

#!/bin/sh

if [ "$#" -eq 0 ]; then
    # No arguments given.
    # Take pattern and string from environment.

    pattern=${PATTERN:?missing}
    string=${STRING:?missing}
else
    # Arguments given.
    # Take pattern and string from 1st and 2nd argument.

    pattern=${1:?argument 1 (pattern) missing}
    string=${2:?argument 2 (string) missing}
fi

# Either of the two `awk` commands from above would work,
# with $pattern and $string inserted in the appropriate
# command line arguments to awk:

awk -v pattern="$pattern" -v text="$string" '
    BEGIN { pattern = "^## " pattern }
    $0 ~ pattern,/^##$/ { if (/^##$/) print text "\n\n" }
    { print }' a.md

You would run this as either

./script.sh 'baba' 'hello world'

or as

export PATTERN='baba' STRING='hello world'
./script.sh

Failing to provide either two command line arguments, or the two environment variables would result in error messages and the awk code would not run at all.

Answer 3

I finally solved it myself using a very useful python script doing exactly what I wanted:

import sys
import os
import re

topic = sys.argv[1]
pattern = "## " + topic

s = r"cat a.md | grep -n '" + pattern + "' a.md | awk -F ':' '/0/ {print$1}'"
#print(s)
pattern = re.compile("##")

stream = os.popen(s)
lineNb = int(stream.read().rstrip())

filename="a.md"
with open(filename, "r") as f:
    for _ in range(lineNb):
            next(f)
    for line_i, line in enumerate(f, 1):
        if re.search(pattern, line):
            index = line_i + lineNb - 1
            #print( "%d\n" % index )
            break

with open(filename, "r") as f:
    contents = f.readlines()
    contents.insert(index - 1, sys.argv[2] + "\n\n")

with open(filename, "w") as f:
    contents = "".join(contents)
    f.write(contents)

could be optimized further probably, any advice welcome.