Prefixing and appending blocks of text to a list of files

Question

I'm trying to prefix and append blocks of text to a list of files. Here is where I am so far. The sticking point is the sed -i "1i \$prefix" "$file" && line. sed won't substitute the value of prefix in. I tried to follow various threads about this on unix.sx and a couple of other places, but just got a headache.

Can someone tell me how to fix this? If it is too complicated I'm Ok with using something else instead of sed.

This is closely related to How do I append text to the beginning and end of multiple text files in Bash?, which is where I got the code below from. The difference is that the question does not cover expanding a variable, and also in my case the strings in question are multiline.

filelist=(foo.tex bar.tex)

prefix='\documentclass[12pt]{article}                                                                                                                                       
\usepackage{myarticle}                                                                                                                                                      
%\xpretocmd{\opening}{\insertname}{}{}                                                                                                                                      
\begin{document}                                                                                                                                                            
%\insertname                                                                                                                                                                
\begin{verbatim}'

suffix='\end{verbatim}                                                                                                                                                      
\end{document}'                                                                                                                                                                 

for file in "${filelist[@]}"; do
  sed -i "1i \$prefix" "$file" &&
  echo "$suffix" >> "$file"
done

Answer 1

How about (assuming your shell has process substitution):

for file in "${filelist[@]}"; do
    cat <(printf "%s" "$prefix") "$file" <(printf "%s" "$suffix") > "$file"_$$\ 
     && mv "$file"_$$ "$file"
done

or, better, in Perl (untested):

perl -MTie::File -e '
    @ARGV//=<STDIN>;
    chomp(@ARGV);
    for(@ARGV){
        tie @lines,"Tie::File",$_;
        @lines=($ENV{prefix} @lines $ENV{suffix})
    }' "${filelist[@]}"

For an alternative approach, if the prefix and suffix are fixed, see the following question (which also happens to be about (La)TeX :) ):

• extracting and copying parts of tex files into new tex files

Answer 2

With zsh:

zmodload zsh/mapfile
for i ($filelist) mapfile[$i]="$prefix
$mapfile[$i]$suffix
"

With ksh93 or bash (or zsh):

for file in "${filelist[@]}"; do
  {
    rm -- "$file" && {
      printf '%s\n' "$prefix"
      cat
      printf '%s\n' "$suffix"
    } > "$file"
  } < "$file"
done

Answer 3

The case is similar to this: Appending a string containing escape character with sed

I suggest the same answer (adapted):

for file in "${filelist[@]}"; do
  sed -i "1i\\
$(echo -E "$prefix" | sed -e 's/\\/\\\\/g' | sed -e '$! s/$/\\/')" "$file" &&
  echo "$suffix" >> "$file"
done

The sed command i requires each line except the last to be terminated with a backslash (this was missing from the referred answer). Also, backslashes need to be doubled, so sed won't try to interpret them. The echo outputs the contents of the variable $prefix. Next in the pipeline, the sed command doubles the backslashes. The second sed command adds backslashes at the end of every line except the last.

EDIT How the sed program $! s/$/\\/ works:

First, the address $ means to execute the command that follows on the last line. $! negates that, so the command will be executed on all lines except the last.

Then, the s/// command does substitution. It will substitute the empty string at the end of the line, denoted by $, with a backslash. But the backslash is a special character, so we need to escape it with another backslash for sed to read it correctly.

Answer 4

Here are a few choices, none of which use sed. I find that in general, trying to get sed to play nice with external variables is rarely worth the effort.

Shell

for file in "${filelist[@]}"; do 
  tmp=$(mktemp); 
  printf "%s\n%s\n%s\n" "$prefix" $(cat "$file") "$suffix" > "$tmp" && 
  mv "$tmp" "$file"; 
done

Perl/Shell

for file in "${filelist[@]}"; do 
  tmp=$(mktemp); 
  perl -lpe 'BEGIN{print $ENV{prefix}}END{print $ENV{suffix}}' $file 
  mv "$tmp" "$file"; 
done

Pure Perl

This one has the advantage of not relying on external modules:

perl -le 'foreach (@ARGV){
           open($f,"+<","$_"); @a=<$f>; 
           print $f "$ENV{suffix}\n@a$ENV{prefix}"
          }' "${filelist[@]}"

NOTE:

The variables need to be exported in order for the Perl solutions to work, otherwise, they won't be available in the %ENV hash.