Using sed to replace only inside a regexp substring

Question

I have a log where i want to apply a replace just inside a regexp match text.

Example, take this log line:

date machine  text random text and yet more random text - status code

i want o replace the all spaces by a _ inside the text area, without replacing all other spaces in the log. the output would be this:

date machine  text_random_text_and_yet_more_random_text - status code

To match the area i want to replace i have this regexp:

/machine \(.*\) - /

As the text is not standard, i can have one space to 20, so its hard to match it directly, so i match the start and the end of the substring.

Trying to use it i tried this:

sed `/machine \(.*\) - /   s/ /_/g '  logfile

but of course, it will replace all spaces in the log, not just the matched substring.

I managed to do it with awk, by iterating and printing each field until i find the machine, where i change the OFS="_" and restore it to space when i find the -. It works... yet, i was curious if this is possible to solve using sed.

Thanks

I don't know what sed supports when it concerns the few 'advanced' regex syntax, but with PCRE, you can do it like that. — Jerry
– Jerry, Commented Oct 10, 2013 at 18:57
Sed don't have PCRE, but that is a interesting site! thanks! — higuita
– higuita, Commented Oct 10, 2013 at 19:04

potong · Accepted Answer · 2013-10-10 19:57:28Z

1

This might work for you (GNU sed):

sed -r 's/(\S+\s+){2}/&\n/;s/\s+-/\n&/;h;y/ /_/;G;s/.*\n(.*)\n.*\n(.*)\n.*\n/\2\1/' file

answered Oct 10, 2013 at 19:57

potong

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1 Comment

higuita Over a year ago

Thanks, this works and uses sed!! i had tried to inserting newlines to break the log, but in my attempt i required several sed commands and didn't feel right. Your solution is looks perfect!

Jotne · Accepted Answer · 2013-10-11 04:43:20Z

1

Since there are two space before text you like to have with underscore and space - space after, you can do like this:

awk -F "  | - " '/machine/ {gsub(/ /,"_",$2)}1' file
date machine text_random_text_and_yet_more_random_text status code

edited Oct 11, 2013 at 4:43

answered Oct 10, 2013 at 19:47

Jotne

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2 Comments

higuita Over a year ago

that }1 is unknown for me... can you explain it, or point me to some doc? i don't know even how to search for that in google!! :) i can see it prints the line, but changing the number to other than 0 does the same thing.

Jotne Over a year ago

1 does mean print any line. Its always true, so it will do the default action, print. It could be written like this 1 {print $0}. So this awkwill change value of filed $2, when its machine, and then the 1 does print all lines, including the modified lines.

anubhava · Accepted Answer · 2013-10-10 19:20:26Z

0

Here is one gnu-awk command to solve this:

s='date machine text random text and yet more random text - status code'
awk '{gsub(/ /, "_", $2); print $1 " machine " $2 " - " $3}' FS='machine *| *- *' <<<"$s"

date machine  text_random_text_and_yet_more_random_text - status code

answered Oct 10, 2013 at 19:20

anubhava

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Zsolt Botykai · Accepted Answer · 2013-10-10 19:48:48Z

0

Another awk solution might be:

awk '{
    # Capture the stringpart in `a`rray
    match($0,"machine  (.*) -",a)
    # Make the changes
    gsub(" ","_",a[1])
    print gensub("machine (.*) -","machine  " a[1] " -","g")
}' INPUTFILE

answered Oct 10, 2013 at 19:48

Zsolt Botykai

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glenn jackman · Accepted Answer · 2013-10-10 20:28:46Z

0

Perl:

echo "date machine  text random text and yet more random text - status code" | 
perl -pe 's/(?<=machine  )(.*)(?= - )/ ($repl = $1) =~ s{\s}{_}g; $repl /e'

date machine  text_random_text_and_yet_more_random_text - status code

answered Oct 10, 2013 at 20:28

glenn jackman

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