Adding a header to source files with Bash - bash

Question

I have a script that adds a string C++ source files:
for f in $(find . -name '*.h' -or -name '*.cpp');
do sed -i '1s/^/<added text> /' $f;
done;
How to make it add a multiline variable value?
Tried this, but with not success:
h=$'//Copyright 2021 My Corporation\n//Authors: me and others\n'
variable h becomes single line.

Answer 1

Use ed, not sed, to edit files.
You also don't need to use find to locate the files if you're using bash:
#!/usr/bin/env bash
h=$'//Copyright 2021 My Corporation\n//Authors: me and others\n'
# Turn on recursive globbing and extended globbing and have patterns that
# fail to match expand to an empty string
shopt -s globstar extglob nullglob
for f in **/*.#(h|cpp); do
# Add the contents of the variable h at the beginning of the file
# Note: no lines in $h should be just a period as that signals end of
# text input mode.
ed -s "$f" <<EOF
1i
$h
.
w
EOF
done
If you must use sed for some reason, you also want to use its i\ command, not s (People tend to forget that sed even has other commands), which inserts the following lines of text until one without a backslash at the end marks the last line of input. Some bash parameter expansion to massage your variable into the appropriate form is needed, of course:
#!/usr/bin/env bash
h=$'//Copyright 2021 My Corporation\n//Authors: me and others\n'
# Add a newline at the very beginning, and a backlash at the end
# of each line
h=$'\n'"${h//$'\n'/$'\\\n'}"
# Or just format the original string appropriately at the start
# h=$'\n//Copyright 2021 My Corporation\\\n//Authors: me and others\\\n'
shopt -s globstar extglob nullglob
for f in **/*.#(h|cpp); do
sed -i -e "1i\\$h" "$f"
done
# If using GNU sed, you can avoid the loop:
# sed -si -e "1i\\$h" **/*.#(h|cpp)

Answer 2

sed can be a bit temperamental when dealing with embedded (single-character) \n's; we can get around this a couple ways ...
Sample input file:
$ cat xx
1
2
3
A couple sed ideas depending on how the ${h} variable is defined:
1) ${h} defined with literal/single-char \n:
$ h=$'//Copyright 2021 My Corporation\n//Authors: me and others\n'
$ sed "1 s|^|${h//$'\n'/\\n}|" xx
Where:
1 s|^| - line 1, replace start of line with ...
${h//$'\n'/\\n} - change all single-char \n into 3-char \\n (escaped \ + n)
NOTE: because / characters show up in the data we need a different delimiter for the sed command, hence the |
2) ${h} defined with 2-char \ + n:
$ h='//Copyright 2021 My Corporation\n//Authors: me and others\n'
$ sed "1 s|^|${h//\/\\}|" xx*
Where:
1 s|^| - line 1, replace start of line with ...
${h//\/\\} - escape all \ (NOTE: this could cause issues with \ that are not to be interpreted as control characters)
NOTE: because / characters show up in the data we need a different delimiter for the sed command, hence the |
Both of these generate:
//Copyright 2021 My Corporation
//Authors: me and others
1
2
3
Once OP is satisfied with the result the -i flag can be added to perform the inplace update.

Answer 3

Using sed is overkill and limit you with sed syntax.
Use cat instead:
#!/usr/bin/env bash
# Some helpful settings to avoid editing the core code
corporation='Example INC'
authors=(
'me'
'someone'
'someone-else'
)
# Capture the year (require bash 4.2+)
# If older bash, use year="$(date '+%Y')"
printf -v year '%(%Y)T'
# Be sure tmp_file variable does not exist (may have been exported)
unset tmp_file
# Prepare EXIT trap to clean-up temporary file
trap 'rm -f -- "$tmp_file"' EXIT
# Safely create a temporary file to hold changes
tmp_file="$(mktemp)"
# Find .h or .cpp files and make it a null delimited records stream
find . \( -name '*.h' -or -name '*.cpp' \) -print0 |
# Iterate the null delimited file names
while read -r -d '' cpp_file; do
# Skip files already containing the copyright header
tail -n2 "$cpp_file" | grep -qF ' * Copyright' && continue
# If successfully merging here-document header with file
# into the temporary file
if cat - "$cpp_file" >"$tmp_file" <<EOF
/*
* Copyright ${year} ${corporation}
* Authors: ${authors[*]}
*
*/
EOF
# then copy the temporary file over
then cp "$tmp_file" "$cpp_file"
fi
done