How to add literal text to the Unix 'cat' command

Question

I'm trying to cat some files together, while at the same time adding some text between files. I'm a Unix newbie and I don't have the hang of the syntax.

Here's my failed attempt:

cat echo "# Final version (reflecting my edits)\n\n" final.md echo "\n\n# The changes I made\n\n" edit.md echo "\n\n#Your original version\n\n" original.md > combined.md

How do I fix this? Should I be using pipes or something?

Answer 1

A process substitution seems to work:

$ cat <(echo 'FOO') foo.txt <(echo 'BAR') bar.txt
FOO
foo
BAR
bar

You can also use command substitution inside a here-document.

$ cat <<EOF
FOO
$(< foo.txt)
BAR
$(< bar.txt)
EOF

Answer 2

Use a command group to merge the output into one stream:

{
   echo -e "# Final version (reflecting my edits)\n\n"
   cat final.md 
   echo -e "\n\n# The changes I made\n\n"
   cat edit.md 
   echo -e "\n\n#Your original version\n\n"
   cat original.md
} > combined.md

There are tricks you can play with process substitution and command substitution (see Lev Levitsky's answer) to do it all with one command (instead of the separate cat processes used here), but this should be efficient enough with so few files.