I need to remove first three lines of multiple markdown files structured like that:

|- Folder
  | - 01-07-22.md
  | - 02-07-22.md
  | - 03-07-22.md
  | - ...

I would like to do this with Mac Terminal (if possible) because I have no expertise with any coding language and thus I don't have any coding platform installed on my computer.

Also I would like to know if other than deleting first 3 lines is possible to add "##" at the very beginning of every document.

What works:

• This work:

  sed -i '' '1,3d' Folder/*.md
  

• The following command works also:

  sed -i '' '1i\
  ##' *.md
  

  But it does not add a new line before the first line.
• This does not work at all:

  sed -i '' '1s
  /^/##/' *.md
  

How to add an empty line at the beginning and "##" at the beginning of the now second line? Explaination: From this:

# First line of example .md file
Second line of example .md
...

To this:

### First line of example .md file
Second line of example .md
...

CodePudding user response：

You should be able to use (GNU) sed. I hope that the Mac version supports all the required flags and features.

To delete the first 3 lines:

sed -i '1,3d' Folder/*.md

To prepend the line ## to every file:

sed -i '1i##' Folder/*.md

To prefix the existing first line with ##:

sed -i '1s/^/##/' Folder/*.md

The original files are overwritten without confirmation, but you can specify -i.bak to create backup files, e.g. Folder/01-07-22.md.bak. Specify -i '' to disable backup file creation.

Certain sed implementations might always require an argument after -i, so go with -i.bak or -i .bak.

If prepending a line does not work, try a different syntax (the newline is important):

sed -i .bak '1i\
##' Folder/*.md

If that doesn't work either, there's another form how sed could be invoked:

sed -i .bak -e '1i\' -e '##' Folder/*.md

If you want to modify the first line and add an empty line before it, e.g. transforming

1
2
3

into

##1
2
3

would require you to use the following command:

sed -i .bak '1s/^/##/;1i\

' Folder/*.md