skip over a pattern in sed - bash

Question

I wrote a correctly working sed script which replaces multiple spaces with single space between tokens (it skips lines with # or //) :
#!/bin/sed -f
/.*#/ !{
/\/\//n
# handle more than one space between tokens
s/\([^ ]\)\s\+/\1 /g
}
i run it on ubuntu like this: ./spaces.sed < spa.txt
spa.txt:
/** spa.txt text
date : some date
hih+jjhh jgjg
if ( hjh>=hjhjh )
y **/
# this is a comment
// this is a comment
lines begins here ;
/****** this line is comment ****/
some more lines
// again comment
more lines words
/** again multi line co
mmment it
comment line
follows till here**/
file ends
now i want to add the functionality that script should skip over lines between a pattern (pattern can be distributed in multiple lines). This is the pattern: /* and */
I tried many things but of no use:
#!/bin/sed -f
/.*#/ !{
/\/\*/,/\*\// {
/\/\*/n #it skips successfully the /* line
n #also skips next line
/\*\// !{
}
}
/\/\//n
# handle more than one space between tokens
s/\([^ ]\)\s\+/\1 /g
}
but script isn't working as expected.
Expected output:
/** spa.txt text
date : some date
hih+jjhh jgjg
if ( hjh>=hjhjh )
y **/
# this is a comment
// this is a comment
lines begins here ;
/****** this line is comment ****/
some more lines
// again comment
more lines words
/** again multi line co
mmment it
comment line
follows till here**/
file ends
suggestions?
Thanks

Answer 1

I'd re-engineer the script a bit, to handle # and // comments on their own. With the /* … */ comments, you have to deal with single-line and multi-line variants separately. I'd also use the [[:space:]] notation to spot spaces or tabs. I prefer to avoid backslashes (an aversion caused by working with troff in the days of my youth — if you've never needed 16 backslashes in a row to get the desired effect, you've not suffered enough), so I use \%…% to choose the % character as the search marker instead of / (which means there's no need to escape the slashes in the pattern with a backslash), and I use [*] instead of \*. The { p; d; } notation prints the current line and then deletes it and moves onto the next line. (Using n appends the next line to the current line; it isn't what you need.). The second semicolon isn't required by GNU sed but is by BSD (macOS) sed. The spaces in those braces are optional but make it easier to read.
Putting this together, you might have spaces.sed like this:
#!/bin/sed -f
# Comments with a #
/#/ { p; d; }
# Comments with //
\%//% { p; d; }
# Single line /* ... */ comments
\%/[*].*[*]/% { p; d; }
# Multi-line /* ... */ comments
\%/[*]%,\%[*]/% { p; d; }
s/\([^[:space:]]\)[[:space:]]\{2,\}/\1 /g
On your sample data (thanks for including it!), this produces:
/** spa.txt text
date : some date
hih+jjhh jgjg
if ( hjh>=hjhjh )
y **/
# this is a comment
// this is a comment
lines begins here ;
/****** this line is comment ****/
some more lines
// again comment
more lines words
/** again multi line co
mmment it
comment line
follows till here**/
file ends
That looks like what you wanted.
Limitations
It doesn't remove multiple spaces at the start of a line.
the leading blanks are not removed.
If you have a line with multiple spaces and // or #, the multiple spaces remain:
these spaces // survive
so do # these
If you have multiple single line comments on a single line, you don't get spaces removed in between them:
/* these */ spaces are not /* removed */
If you have a single-line comment and the start of a multi-line comment on a single line, the multi-line comment is not spotted. Similarly, if you have a multi-line comment that ends on a line and has a single-line comment starting after it, then if there are any multiple spaces between the end of the one comment and the start of the next, they are not handled.
/* this */ is not /* handled
very well */ nor are these /* spaces */
This doesn't deal with the subtleties of backslash-newline in the middle of a start or end comment symbol, nor with backslash-newline at the end of a // comment. Only brain-dead programs (or programmers) produce such comments, so it shouldn't be a real problem. Fortunately, you're not writing a compiler; those have to deal with the nonsense. And don't get me started on trigraphs!
It doesn't handle comment-like sequences inside strings (or multi-character character constants):
"/* this is not a comment */"
'/*', ' ', '*/'
However, most of these issues are subtle enough that you're probably OK without dealing with them. If you must deal with them, then you need a program, not a sed script (assuming you value your sanity).