How to replace a character with the output of some commands using sed?

mamun2015 · 03-16-2010, 01:54 AM

Hi guys,

I was facing problems with the following scenario for the last several hours, can anyone help me out?

rm -f /www/emailout/template.html

TODAY=`date '+%d-%m-%y'`

DBRUN=`ps ax | grep dtd `

sed -e 's/ncTODAY/'"$TODAY"'/g' -e "s/ncdbrun/'"$DBRUN"'/g" /www/emailout/test1.html > /www/emailout/template.html

But, I can't get the output of $DBRUN ?

What would be the solution, can anyone please fix the problem for me?

GrapefruiTgirl · 03-16-2010, 02:12 AM

Your second sed -e expression is double-quoted (good), but the $DBRUN variable itself is also double-quoted (problem), so put the second -e expression in single quotes. Making that correction fixed it for me when I tested it.

Even simpler, would be to double-quote the -e expressions, and use NO quotes at all around the $VARIABLES inside the sed expressions. That way is simpler, and easier to read.

Examples:

Code:

sasha@reactor: TODAY=$(date '+%d-%m-%y')
sasha@reactor: DBRUN='BLARG!! RAWK!!!'

Your way:
sasha@reactor: echo 'ncTODAY...ncdbrun' | sed -e 's/ncTODAY/'"$TODAY"'/g' -e "s/ncdbrun/'"$DBRUN"'/g"
sed: -e expression #2, char 18: unterminated `s' command

My way:
sasha@reactor: echo 'ncTODAY...ncdbrun' | sed -e 's/ncTODAY/'"$TODAY"'/g' -e 's/ncdbrun/'"$DBRUN"'/g'
16-03-10...BLARG!! RAWK!!!

The simpler way (notice the quotes):
sasha@reactor: echo 'ncTODAY...ncdbrun' | sed -e "s/ncTODAY/$TODAY/g" -e "s/ncdbrun/$DBRUN/g"
16-03-10...BLARG!! RAWK!!!
sasha@reactor:

Sasha

GlennsPref · 03-16-2010, 02:23 AM

Brilliant Sasha!

off topic, I'm learning sed.

Glenn

Quote:

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Tinkster · 03-16-2010, 02:29 AM

Quote:

Originally Posted by GlennsPref

Brilliant Sasha!

off topic, I'm learning sed.

Glenn

Actually ... that's the SHELL doing the variable expansion,
not sed. sed doesn't care about what quotes you use.

Cheers,
Tink

David the H. · 03-16-2010, 02:51 AM

Yes, the quoting on the second expression is all messed up. Remember, quotes act more like toggles than enclosures. Also, single-quotes are escaped (meaning they lose their special meaning) when under the effect of double quotes, and vice-versa.

Let's simplify your two expressions.
expression 1:

Code:

-e 'string'   "$variable"  'string'
   ^      ^   ^         ^  ^      ^
  on     off on        off on    off

This one is good. single quote no. 2 toggles off escaping, then the double-quotes turn it back on again, while allowing the variable to expand. Then single quote no. 3 turns it back on again to protect the string.

expression 2:

Code:

-e " string '   " $variable "   ' string "
   ^        ^   ^           ^   ^        ^
  on        x  off         on   x       off

Not so good here. Both of the single quotes are "inside" double quotes, and so are being treated literally as part of the string expressions (meaning sed will probably not match anything. The variable is outside of the quotes and so it's allowed to expand, but since it's not protected in any way, word-splitting will take place on the contents, probably breaking the expression.

As Sasha said though, the best thing to do here is to simply enclose the whole thing in a single set of double-quotes. The variables will expand, then the whole thing will be sent to sed as a single expression.

Code:

-e "string $variable string"

GrapefruiTgirl · 03-16-2010, 02:54 AM

@ David -- that's a really good way of putting it:

The quotes act like toggles rather than enclosures.

I say: The less quotes the better!

GlennsPref · 03-16-2010, 02:55 AM

Just goes to show how far I have to go....lol!

I'm using the Z shell(zsh) confuses me, but works nicely for what I need (aliases, etc).
Thank you, regards Glenn

regards Glenn

GrapefruiTgirl · 03-16-2010, 02:59 AM

@ Glenn,

I've never used zsh, but you surely know that you can have aliases in other shells too, yes? Like Bash, Dash, etc..

Is there a particular reason you use zsh?

(Sorry OP, not trying to get off topic here

but at least the question is hopefully answered!)

GlennsPref · 03-16-2010, 04:12 AM

I came across it reading a Jerry Peek article on LJ(Linux Journal) (if my memory serves me correctly)

It has a lot of globing effects I know nothing about, but I like the colours of the text (lol, candy bait) and the ease of set up. been using it for years, don't know why. I guess someone suggested it to me.

But it works, and it works well.

Sorry for the hijack OP, Glenn

mamun2015 · 03-16-2010, 04:41 AM

Quote:

Originally Posted by GrapefruiTgirl

Your second sed -e expression is double-quoted (good), but the $DBRUN variable itself is also double-quoted (problem), so put the second -e expression in single quotes. Making that correction fixed it for me when I tested it.

Even simpler, would be to double-quote the -e expressions, and use NO quotes at all around the $VARIABLES inside the sed expressions. That way is simpler, and easier to read.

Examples:

Code:

sasha@reactor: TODAY=$(date '+%d-%m-%y')
sasha@reactor: DBRUN='BLARG!! RAWK!!!'

Your way:
sasha@reactor: echo 'ncTODAY...ncdbrun' | sed -e 's/ncTODAY/'"$TODAY"'/g' -e "s/ncdbrun/'"$DBRUN"'/g"
sed: -e expression #2, char 18: unterminated `s' command

My way:
sasha@reactor: echo 'ncTODAY...ncdbrun' | sed -e 's/ncTODAY/'"$TODAY"'/g' -e 's/ncdbrun/'"$DBRUN"'/g'
16-03-10...BLARG!! RAWK!!!

The simpler way (notice the quotes):
sasha@reactor: echo 'ncTODAY...ncdbrun' | sed -e "s/ncTODAY/$TODAY/g" -e "s/ncdbrun/$DBRUN/g"
16-03-10...BLARG!! RAWK!!!
sasha@reactor:

Sasha

Can you plase, change your DBRUN variable like this:

DBRUN=`ps ax`

Still I am getting the error? I don't know at least it should show as a string, there may be formatting problem.....please help,man!!

mamun2015 · 03-16-2010, 04:58 AM

Oh Shasha, I forgot to thank you......thanks a lot,man. Though I already worked similar things what you did for me, [ Copied from the previous one:
Can you plase, change your DBRUN variable like this:

DBRUN=`ps ax`

Still I am getting the error? I don't know at least it should show as a string, there may be formatting problem.....please help,man!! ]

mamun2015 · 03-16-2010, 06:45 AM

Hi guys,

Is it possible to do the following:

TODAY=$(date '+%d-%m-%y')
DBRUN=`ps ax`

echo 'ncTODAY...ncdbrun' | sed -e "s/ncTODAY/$TODAY/g" -e "s/ncdbrun/$DBRUN/g"

I couldn't find anyway out,can anyone please help me?

jamescondron · 03-16-2010, 06:50 AM

What happens when you do it? What output are you expecting?

pixellany · 03-16-2010, 07:00 AM

first, "ps ax" on my machine produces 2 screenfuls of details on processes. Was it your intent to insert that all on one line in place of "ncbrun"?

Your syntax seems OK, but it is not at all obvious what the ultimate objective is.

mamun2015 · 03-16-2010, 07:36 AM

Quote:

Originally Posted by pixellany

first, "ps ax" on my machine produces 2 screenfuls of details on processes. Was it your intent to insert that all on one line in place of "ncbrun"?

Your syntax seems OK, but it is not at all obvious what the ultimate objective is.

Thanks for your question!

Basically, I need to search for a word then I need to replace it with the output of "ps ax", each process in new line.

please,reply.