topic Re: SED to delete first three occurances... in Operating System - Linux

SED to delete first three occurances...

jmckinzie — Thu, 24 May 2007 13:16:25 GMT

I have a file with 5 lines.
all of which contain the switch -t.

I want to move the -t off the first three occurances and leave an remaining ones alone.

I have this command but it removed all -t within the file.

sed 's/-t//' filename

Any ideas?

Re: SED to delete first three occurances...

Ivan Ferreira — Thu, 24 May 2007 13:24:50 GMT

Try with:

sed '1,3 s/-t//' filename

Re: SED to delete first three occurances...

James R. Ferguson — Thu, 24 May 2007 13:25:40 GMT

Hi Jody:

If by "occurances" you mean "lines":

# sed -e '1,3s/-t//' filename

Regards!

...JRF...

Re: SED to delete first three occurances...

jmckinzie — Thu, 24 May 2007 13:30:35 GMT

No, i do not want to delete the lines, just the -t

Re: SED to delete first three occurances...

jmckinzie — Thu, 24 May 2007 13:32:00 GMT

Ivan,

That did not work.

Appreciate the help.

Re: SED to delete first three occurances...

Patrick Wallek — Thu, 24 May 2007 13:36:42 GMT

What didn't work?

I just tried the following:

# cat test
-t -b
-t -c
-t -d
-t -e
-t -f

# sed 1,3s/-t// test
-b
-c
-d
-t -e
-t -f

Re: SED to delete first three occurances...

James R. Ferguson — Thu, 24 May 2007 13:37:23 GMT

Hi (again) Jody:

# cat .filename
line 1 -t
line 2 -t
line 3 -t
line 4 -t
line 5 -t

# sed -e '1,3s/-t//' filename
line 1
line 2
line 3
line 4 -t
line 5 -t

Regards!

...JRF...

Re: SED to delete first three occurances...

Sandman! — Thu, 24 May 2007 13:38:19 GMT

# sed '1,3 s/$.*$-t/\1/g' file

Re: SED to delete first three occurances...

jmckinzie — Thu, 24 May 2007 13:42:21 GMT

filename = /tmp/cron

cat /tmp/cron

00 03 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 12 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t > /tmp/tiscan 2>&1
00 17 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -t -o > /tmp/tiscan 2>&1

sed '1,3 s/$.*$-t/\1/g' /tmp/cron

doesn't work
neither does the one above that.

I wonder why?

Re: SED to delete first three occurances...

Patrick Wallek — Thu, 24 May 2007 13:48:06 GMT

It worked for me.

Using your data in a file called test.

$ sed 1,3s/-t// test
00 03 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o
00 12 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o > /tmp/tis
can 2>&1
00 17 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -t -o > /tmp/t
iscan 2>&1

Re: SED to delete first three occurances...

James R. Ferguson — Thu, 24 May 2007 13:52:54 GMT

Jody:

"doesn't work"

Exactly what output do you get? Any errors?

# which sed

...reports?

# wc -l filename

...reports?

Regards!

...JRF...

Re: SED to delete first three occurances...

jmckinzie — Thu, 24 May 2007 13:56:19 GMT

ok, does this say for the first three lines?

what if these entries aren't in the first three lines?

# cat cron
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 12 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t > /tmp/tiscan 2>&1
00 17 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -t -o > /tmp/tiscan 2>&1

now with SED.....

# sed 1,3s/-t// cron
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o
00 12 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t > /tmp/tiscan 2>&1
00 17 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -t -o > /tmp/tiscan 2>&1

with additional lines?

# sed 1,3s/-t// cron
ewfwefj
wefwefwef
wefwefwef
wefwefwe
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 06 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t
00 12 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -o -t > /tmp/tiscan 2>&1
00 17 * * 0-6 /opt/TIscan/bin/scan -c /opt/TIscan/etc/sysscan.cfg -t -o > /tmp/tiscan 2>&1

Re: SED to delete first three occurances...

James R. Ferguson — Thu, 24 May 2007 14:07:38 GMT

Jody:

> what if these entries aren't in the first three lines?

You never made that clear. However:

# perl -nle 'm/-t/ && $i++ <=2 && s/-t//;print' filename

Regards!

...JRF...

Re: SED to delete first three occurances...

jmckinzie — Thu, 24 May 2007 14:23:08 GMT

James,

That worked....thanks.

Sorry for my vague description.

for the sake of my learning sed and perl for that matter, could you explain what each character is doing?

perl -nle 'm/-t/ && $i++ <=2 && s/-t//;print'

perl -n (???) l (octal-what does that mean?) e (followed by a command) 'm/-t (i do not know) && counter <=2 (0-2=3) s/-t//; print'

TIA

Re: SED to delete first three occurances...

James R. Ferguson — Thu, 24 May 2007 14:36:20 GMT

Hi (again) Jody:

# perl -pe 'm/\s-t\s/ && $i++ <=2 && s/-t//'

...is a wee-bit shorter and safer.

The '-p' says read (a line) and print. The '-n' in the first variation says read but don't automatically print.

The m/\s-t\s/ says match the '-t' if it is bounded by a whitespace (space, tab) character on either side. After all, we don't match things like "this-thing".

The && means AND.

The variable $i is undefined but for Perl's purpose will be zero when the code begins. Thus for the values 0, 1 and 2 of $i, we will substitute nothing for the regular expression /-t'/.

In all, we read the file(s) specified on the command line, looping over each line. If we find a " -t " and we haven't counted three times, we remove it from the line we read. In any event, every line of the file gets printed.

Regards!

...JRF...

Re: SED to delete first three occurances...

jmckinzie — Thu, 24 May 2007 14:47:50 GMT

Thanks a bunch...this helped significantly.

Points have been assigned to all!

Re: SED to delete first three occurances...

James R. Ferguson — Thu, 24 May 2007 20:50:51 GMT

Hi (again) Jody:

Although a bit more advanced, this solution is a bit more rigorous:

# perl -pe 'if ($i<3){$i++ if s/((?<=\W)|\A)-t(?=\W|\z)//g}' filename

All occurances of the pattern "-t" is snipped from the number of lines tested against $i. The pattern is sought where it is left-bounded by a non-word character or the begining of the line; and it is right-bounded by a non-word character or the end of the line.

Regards!

...JRF...

Re: SED to delete first three occurances...

Dennis Handly — Thu, 24 May 2007 22:33:23 GMT

If you really really want to use sed(1) and gotos, you can try:
sed -e '
1,/-t/ {
s/-t//g
t second
}
: second
1,/-t/{
s/-t//g
t third
}
: third
1,/-t/{
s/-t//g
t fourth
}
: fourth
' filename

I have no idea why it works, except sed(1) must remember where it found the first "-t" for the first block and not reevaluate it.