sed delete line containg a pair of () parenthesis - sed

Question

Hi I have created a large set of sed commands to manipulate a text file.
The one last thing I cant seem to solve is where a line simply consists of a pair of ()
some text
()
more text
(leave this line as is)
I want to delete the entire () line
some text
more text
(leave this line as is)
in my script
this sed command -e '/()/ s/()//' can find and remove the () but leaves a line behind
some text
more text
(leave this line as is)
Here is a snipped version of the bigger picture
FILEPATH=*.chordpro
for fn in $FILEPATH; do
echo $fn
fnbak=$fn.bak
mv "$fn" "$fnbak" #Create an untouched backup
sed `: # these are comments` \
`: # Insert after subtitle; author,book,keywords,tempo,time` \
-e '/^{subtitle.*/a {author:mds}\n{book:CatStevens}\n{keywords:70s,Tillerman}\n{tempo:120}\n{time:4/4}' \
-e 's/{subtitle:/{artist:/' `: # swap subtitle for artist` \
-e 's/{time:/{duration:/' `: # modifiy original meta "time" for "duration"` \
....lots of other commands
`: # Tidy up` \
-e '/()/ s/()//' `: # Remove any () pairs created by script` \
"$fnbak" >"$fn"
Here is snippet of the input test cases.
{c:Verse2}
{c: Verse 2: Bass single}
{c: Verse 2 Rock it}
{c: verse 1}
{c: verse 1}
{c: Verse 1:}
{c:Verse}
Here it is converted. Out#1
Verse 2:
()
Verse 2:
( Bass single)
Verse 2:
( Rock it)
Verse 1:
()
Verse 1:
()
Verse 1:
()
Verse :
()
This is the tidy up result using -e '/()/ s/()//' Out#2
Verse 2:
Verse 2:
( Bass single)
Verse 2:
( Rock it)
Verse 1:
Verse 1:
Verse 1:
Verse :
This is the result using -e '/()/d'
Verse 2:
( Bass single)
Verse 2:
( Rock it)
where has everything after Rock it gone and why????
NOTE: ok it has something to do with it being in the loop/interaction with other sed commands.
If I put Out#1 into a file on its own and run just the sed -e '/()/d' command on it, it works
This is what I hoped to achieve
Verse 2:
Verse 2:
( Bass single)
Verse 2:
( Rock it)
Verse 1:
Verse 1:
Verse 1:
Verse :

Answer 1

Don't write lengthy sed scripts, use awk instead for clarity, efficiency, robustness, portability, etc. Instead of this:
sed `: # these are comments` \
`: # Insert after subtitle; author,book,keywords,tempo,time` \
-e '/^{subtitle.*/a {author:mds}\n{book:CatStevens}\n{keywords:70s,Tillerman}\n{tempo:120}\n{time:4/4}' \
-e 's/{subtitle:/{artist:/' `: # swap subtitle for artist` \
-e 's/{time:/{duration:/' `: # modifiy original meta "time" for "duration"` \
....lots of other commands
`: # Tidy up` \
-e '/()/ s/()//' `: # Remove any () pairs created by script` \
"$fnbak" >"$fn"
try this which I think is the equivalent of what you're doing above but also fixes your code to remove () pairs:
awk '
# Insert after subtitle; author,book,keywords,tempo,time
/^{subtitle/ {
$0 = $0 \
"\n{author:mds}" \
"\n{book:CatStevens}" \
"\n{keywords:70s,Tillerman}" \
"\n{tempo:120}" \
"\n{time:4/4}"
}
{
sub(/{subtitle:/,"{artist:") # swap subtitle for artist
sub/{time:/,"{duration:") # modify original meta "time" for "duration"
....lots of other commands
# Tidy up
# Remove any () pairs created by script
gsub(/\n\()\n/,"\n") # Convert every \n()\n to \n ..
gsub(/\n\()\n/,"\n") # .. done twice to handle \n()\n()\n
gsub(/^\()\n|\n\()$/,"") # Remove ()\n at the start and \n() at the end
gsub(/\()/,"") # Remove every remaining ()
print
}
' "$fnbak" > "$fn"
Your comment says Remove any () pairs created by script but the script you posted cannot create any () pairs so I'm assuming that your lots of other commands can do so and I'm just guessing in my awk script about what it really is you want to do in the "Tidy up" section since you didn't provide any sample input/output we could test against.
By the way, the more common way to modify an input file would be:
fnbak=$(mktemp) || exit 1
cmd 'script' "$fn" > "$fnbak" &&
mv -- "$fnbak" "$fn"
rather than
fnbak=$fn.bak
mv "$fn" "$fnback"
cmd 'script' "$fnbak" > "$fn"
The former only keeps the backup file around long enough to modify the original, only uses a single backup for all files rather than 1 per file, and won't wipe out your original input file if there isn't enough disk space or you don't have write permission to create the backup.
You only have to create the backup file once before entering your loop:
FILEPATH=*.chordpro
fnbak=$(mktemp) || exit 1
for fn in $FILEPATH; do
echo "$fn"
cmd 'script' "$fn" > "$fnbak" &&
mv -- "$fnbak" "$fn"
done
but of course you don't need a loop or temp files at all if you use GNU awk, all you need is:
gawk -i inplace 'script' *.chordpro
(add FNR==1{print FILENAME | "cat>&2"} to the awk script to see the input file names printed as they're worked on).

Answer 2

here's a GNU sed script for you - it allows inline comments so there's no need for complicated quoting
Save it in tmp.sh
#!/bin/bash
# tmp.sh
sed -E '
# strip initial piece
s/\{c: *//
# strip terminal piece
s/ *} *$//
# munge verse with number
s/verse *([0-9]+):? */Verse \1:/i
# munge verse without number
s/verse *$/Verse :/i
# put description on new line
s/: *(.+)$/:\n(\1)/
'
Test with heredoc:
$ ./tmp.sh <<EOF
{c:Verse2}
{c: Verse 2: Bass single}
{c: Verse 2 Rock it}
{c: verse 1}
{c: verse 1}
{c: Verse 1:}
{c:Verse}
EOF
Verse 2:
Verse 2:
(Bass single)
Verse 2:
(Rock it)
Verse 1:
Verse 1:
Verse 1:
Verse :
It's hard to say why your single delete command behaves unexpectedly without seeing the entire script
You could try the relatively new --debug option offered in sed 4.6 - or what I find very useful are the l and = commands to show the state of the line at any point in multiple transformations
My script is more like a starting point for you to compare and troubleshoot your script and to modify for other test cases
Hope it helps