replacing word in shell script or sed

Question

I am a newbie, but would like to create a script which does the following.

Suppose I have a file of the form

This is line1
This is line2
This is line3

This is line4
This is line5
This is line6

I would like to replace it in the form

\textbf{This is line1}
This is line2
This is line3

\textbf{This is line4}
This is line5
This is line6

That is, at the start of the paragraph I would like to add a text \\textbf{ and end the line with } . Is there a way to search for double end of lines? I am having trouble creating such a script with sed. Thank you !

Answer 1

Using awk you can write something like

$ awk '!f{ $0 = "\\textbf{"$0"}"; f++} 1; /^$/{f=0}' input
\textbf{This is line1}
This is line2
This is line3

\textbf{This is line4}
This is line5
This is line6

What it does?

• !f{ $0 = "\\\\textbf{"$0"}"; f++}

  • !f True if value of f is 0 . For the first line, since the value of f is not set, will evaluates true. If its true, awk performs tha action part {}

  • $0 = "\\\\textbf{"$0"}" adds \\textbf{ and } to the line

  • f++ increments the value of f so that it may not enter into this action part, unless f is set to zero

• 1 always True. Since action part is missing, awk performs the default action to print the entire line

• /^$/ Pattern matches an empty line

  • {f=0} If the line is empty, then set f=0 so that the next line is modfied by the first action part to include the changes

Answer 2

An approach using sed

sed '/^$/{N;s/^\(\n\)\(.*\)/\1\\textbf{\2}/};1{s/\(.*\)/\\textbf{\1}/}' my_file

find all lines that only have a newline character and then add the next line to it. ==

^$/{N;s/^\(\n\)\(.*\)/\1\\textbf{\2}/}

mark the line below the blank line and modify it

find the first line in the file and do the same == 1{s/\\(.*\\)/\\\\textbf{\\1}/}

Answer 3

Just use awk's paragraph mode:

$ awk 'BEGIN{RS="";ORS="\n\n";FS=OFS="\n"} {$1="\\textbf{"$1"}"} 1' file
\textbf{This is line1}
This is line2
This is line3

\textbf{This is line4}
This is line5
This is line6