unix command to delete parts of a file

[melissa_benkyo]

hello all! I'd like to ask if there's a unix command that could delete
parts of the file given a string. Example:
Given: File1 which contains
--testing--
test123
--testing--
--hello--
world
--hello--

If my string is hello, the output would be another file or the same
file but without the hello block. So, the output would be
--testing--
test123
--testing--

if anybody knows please help! thanks!

[SW]

melissa_benkyo wrote:

>
> If my string is hello, the output would be another file or the same
> file but without the hello block.

It sounds like you want to eliminate a "block" of text, starting and ending
with a key word on a line of its own. That's not going to be accomplished
with a simple grep as has been suggested, but there are a few equally easy
ways of accomplishing this.

Before we go there, though....might this be a homework assignment that
you're hoping to accomplish today?

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[Taneli Vähäkangas]

In article <304f3217.0307071251.7293969a@posting.google.com >, melissa_benkyo wrote:

> hello all! I'd like to ask if there's a unix command that could delete
> parts of the file given a string. Example:
> Given: File1 which contains
> --testing--
> test123
> --testing--
> --hello--
> world
> --hello--
>
> If my string is hello, the output would be another file or the same
> file but without the hello block. So, the output would be
> --testing--
> test123
> --testing--

If you want to lose the --hello-- / --hello-- limited block, you could
try if sgrep ([url]http://www.cs.helsinki.fi/u/jjaakkol/sgrep.html[/url]) does
what you want.

Taneli

[Andy Zweck]

* melissa_benkyo <wyl_lyf@yahoo.com>:

> hello all! I'd like to ask if there's a unix command that could delete
> parts of the file given a string. Example:
> Given: File1 which contains
> --testing--
> test123
> --testing--
> --hello--
> world
> --hello--
>
> If my string is hello, the output would be another file or the same
> file but without the hello block. So, the output would be
> --testing--
> test123
> --testing--

I assume you want to delete all hello blocks including the "--hello--"
lines. Then

sed -e '/--hello--/,/--hello--/d' < infile > outfile

should suffice. If the command should modify the file rather than
writing a new one,

perl -i -ne 'print unless /--hello--/ ... /--hello--/' thefile

or

perl -0777 -i -pe 's/--hello--.*?--hello--\n//gs' thefile

can mimick that (Perl internally writes a new file and renames it).

-ooo- Andy

[Laurent-jan]

melissa_benkyo wrote:

> hello all! I'd like to ask if there's a unix command that could delete
> parts of the file given a string. Example:
> Given: File1 which contains
> --testing--
> test123
> --testing--
> --hello--
> world
> --hello--
>
> If my string is hello, the output would be another file or the same
> file but without the hello block. So, the output would be
> --testing--
> test123
> --testing--
>
> if anybody knows please help! thanks!

awk '
BEGIN { pr=1 }
{
if (pr==1){
if($0 ~ "--hello--") pr=0
else print
}
else if($0 ~ "--hello--") pr=1
}'

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but not limited to telepathy without the benevolence of the author.

[Kenny McCormack]

In article <1057697526.951081@smirk>,
James T. Dennis <jadestar@idiom.com> wrote:
....

> These awk scripts are just filters; you'd have to use redirection,
> temporary files and renaming (a shell script wrapper around these
> awk commands) to change your file. Alternatively you can use the
> perl -i (in situ edit) switch to force your changes directly into
> the file. I'll leave that (and concerns about robustness and error
> handling --- like if the perl script is killed abruptly in mid-file)
> as exercises to the original poster.

Note that Perl does *not* do in-situ editing. It is just pretend (aka,
syntactic sugar). Perl's -i switch is 100% identical to a wrapper around
an AWK script like this:

tmp=/tmp/tmp.$$
awk ... infile > $tmp
mv $tmp infile

(with, of course, the added proviso that -ibak leaves the original file
intact as foo.bak - again, easily enough implemented in a shell wrapper)

Note that the file systems of Unix and Unix-like systems (including
DOS/Windows) simply do not support in-situ editing - one way or another,
the file has to be re-written from scratch. Now, MTS, on the other hand...

Note also that using "ex" as a scripting utility comes closest (*), but
even then, a temp file is involved (it is kept very well hidden from the
user, however).

(*) And, incidentally, is a good solution to a lot of these Usenet queries,
like, e.g., "how do I delete the last 3 lines of a file?" Generally, "ex"
solutions are clearer and more robust than the typical sed/perl line noise.

[phn@icke-reklam.ipsec.nu]

Kenny McCormack <gazelle@yin.interaccess.com> wrote:

> In article <1057697526.951081@smirk>,
> James T. Dennis <jadestar@idiom.com> wrote:
> ...

>> These awk scripts are just filters; you'd have to use redirection,
>> temporary files and renaming (a shell script wrapper around these
>> awk commands) to change your file. Alternatively you can use the
>> perl -i (in situ edit) switch to force your changes directly into
>> the file. I'll leave that (and concerns about robustness and error
>> handling --- like if the perl script is killed abruptly in mid-file)
>> as exercises to the original poster.

> Note that Perl does *not* do in-situ editing. It is just pretend (aka,
> syntactic sugar). Perl's -i switch is 100% identical to a wrapper around
> an AWK script like this:

> tmp=/tmp/tmp.$$
> awk ... infile > $tmp
> mv $tmp infile

> (with, of course, the added proviso that -ibak leaves the original file
> intact as foo.bak - again, easily enough implemented in a shell wrapper)

> Note that the file systems of Unix and Unix-like systems (including
> DOS/Windows) simply do not support in-situ editing - one way or another,
> the file has to be re-written from scratch. Now, MTS, on the other hand...

Slight misunderstanding seems to have slipped in. UN*X allows perfectly well
a process to read and write ( also known as "update" ) a file. There
is nothing strange about that.


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