The only way to precisely implement a general purpose sh script to strip comments is to implement a sh language parser. In short, the goal would be to implement a sh parser in sh. Anything less would not be dependable for general purpose use. That said, for your needs (whatever they may be), perhaps an 80% solution is satisfactory 99% of the time.
If the input to the comment stripper is not constrained to some restricted format, there will be problems. The "#" is used for purposes other than to introduce a comment. And, even if it had no other use, situations like quoted strings and command substitutions would need to be taken into account.
The following posix-compliant sh script would be mangled by any naive solution.
nocomments.sh:
Code:
#!/bin/sh
echo There is no comment line beginning with a\
# in this file except for the leading '#!/bin/sh', which you may not want removed
echo If this' # was not quoted', I would be a comment
echo $# is the number of positional parameters, not a comment
Note that the above sh script contains no comments, other than the shebang line (#!/bin/sh), which you may not want to strip, depending on your goal.
Verifying the validity of the script, and that the line beginning with a "#" is indeed not a comment:
Code:
$ ./nocomments.sh
There is no comment line beginning with a# in this file except for the leading #!/bin/sh, which you may not want removed
If this # was not quoted, I would be a comment
0 is the number of positional parameters, not a comment
Testing a proposed solution (sorry, danmero, I just picked yours because it's the latest post as I write this ; all others suffer the same shortcomings):
Code:
$ awk '$1!="#" && NF{gsub(/^[\t ]*/,x);sub("#.*",x);print}' nocomments.sh
echo There is no comment line beginning with a\
echo If this'
echo $
The comment-less (shebang excepted) script has been mutilated.
Again, the proposed solutions may be sufficient for your needs; I'm simply pointing out their unsuitability for general purpose use.
Regards,
Alister
P.S. And those are just some posix-compliant possibilities, who knows what madness awaits beyond the standard
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LEARN ABOUT OSF1
vorbiscomment
VORBISCOMMENT(1) Ogg Vorbis Tools VORBISCOMMENT(1)NAME
vorbiscomment - List or edit comments in Ogg Vorbis files
SYNOPSIS
vorbiscomment [-l] [-R] [-e] file.ogg
vorbiscomment -a [ -c commentfile | -t "name=value" ] [-q] [-R] [-e] in.ogg [out.ogg]
vorbiscomment -w [ -c commentfile | -t "name=value" ] [-q] [-R] [-e] in.ogg [out.ogg]
DESCRIPTION
vorbiscomment Reads, modifies, and appends Ogg Vorbis audio file metadata tags.
OPTIONS -a, --append
Append comments.
-c file, --commentfile file
Take comments from a file. The file is the same format as is output by the the -l option or given to the -t option: one element per
line in 'tag=value' format. If the file is /dev/null and -w was passed, the existing comments will be removed.
-h, --help
Show command help.
-l, --list
List the comments in the Ogg Vorbis file.
-q, --quiet
Quiet mode. No messages are displayed.
-t 'name=value', --tag 'name=value'
Specify a new tag on the command line. Each tag is given as a single string. The part before the '=' is treated as the tag name and
the part after as the value.
-w, --write
Replace comments with the new set given either on the command line with -t or from a file with -c. If neither -c nor -t is given,
the new set will be read from the standard input.
-R, --raw
Read and write comments in UTF-8, rather than converting to the user's character set.
-e, --escapes
Quote/unquote newlines and backslashes in the comments. This ensures every comment is exactly one line in the output (or input),
allowing to filter and round-trip them. Without it, you can only write multi-line comments by using -t and you can't reliably dis-
tinguish them from multiple one-line comments.
Supported escapes are c-style "
", "
", "\" and " ". A backslash followed by anything else is an error.
Note: currently, anything after the first " " is thrown away while writing. This is a bug -- the Vorbis format can safely store
null characters, but most other tools wouldn't handle them anyway.
-V, --version
Display the version of vorbiscomment.
EXAMPLES
To just see what comment tags are in a file:
vorbiscomment -l file.ogg
To edit those comments:
vorbiscomment -l file.ogg > file.txt
[edit the comments in file.txt to your satisfaction]
vorbiscomment -w -c file.txt file.ogg newfile.ogg
To simply add a comment:
vorbiscomment -a -t 'ARTIST=No One You Know' file.ogg newfile.ogg
To add a set of comments from the standard input:
vorbiscomment -a file.ogg
ARTIST=No One You Know
ALBUM=The Famous Album
<ctrl-d>
TAG FORMAT
See http://xiph.org/ogg/vorbis/doc/v-comment.html for documentation on the Ogg Vorbis tag format, including a suggested list of canonical
tag names.
AUTHORS
Program Authors:
Michael Smith <msmith@xiph.org>
Ralph Giles <giles@xiph.org>
Manpage Author:
Christopher L Cheney <ccheney@debian.org>
SEE ALSO oggenc(1), oggdec(1), ogg123(1), ogginfo(1)Xiph.Org Foundation December 30, 2008 VORBISCOMMENT(1)
05-03-2010
; all others suffer the same shortcomings):