Ubuntu – Replace spaces in a matched substring with underscores

command linesed

I'm new to the forum so please forgive any syntactical errors in my question.

I'm trying to replace spaces with underscores in a matched substring only. I figured sed would be the best editor for this but I cannot find the proper code to do this.

Sample line from file1 below:

Some text before pattern to match href="./Dynamic Directory name –
Junk_files/irrelevant stuff after match">

Would like to change to this:

Some text before pattern to match
href="./Dynamic_Directory_name_-_Junk_files/irrelevant stuff after
match">

I thought I was close with this cat file1 |sed '/\.\/.*. Junk_files/ { s/ /_/g; }' but all it did was replace all spaces on the matched line with underscores.

Any help with this would be greatly appreciate. Thanks

Best Answer

Through python,

$ echo 'href="./Dynamic Directory name - Junk_files/irrelevant stuff after match"' |
> python -c "import re;
> import sys;
> print re.sub(r'(?<=\./).*?(?=/)', lambda m: m.group().replace(' ', '_'), sys.stdin.read())
> "
href="./Dynamic_Directory_name_-_Junk_files/irrelevant stuff after match"

Through perl,

$ echo 'href="./Dynamic Directory name - Junk_files/irrelevant stuff' | perl -pe '
> s/\s(?=(?:(?!\.\/).)*?\/)/_/g
> '
href="./Dynamic_Directory_name_-_Junk_files/irrelevant stuff

Related Solutions

Ubuntu – Replacing dots (.) in sed

First I would start by testing with echo and piping that into sed, than using a real file. Secondly, you can use a {n} in the extended regex model to denote multiples and limits.

You were pretty much there but your regex expected a leading space.

$ echo 'cheese . . . muffins' | sed -r 's/(\s?\.){3}/ dot dot dot/g'
cheese dot dot dot muffins

Note the \s? is still greedy enough to ruin the output, so I've added a space to the output. You might not want that. I've also made the space optional, so it'll match all of the following:

...
. ..
.. .
. . .
 . . .

Just remove the optional ? flag.

Given your problem with unicode (in the comments) you can force the data to its ASCII equivalence with iconv and then sed it:

$ iconv -f utf-8 -t ascii//translit sed-dots | sed -r 's/(\s?\.){3}/ dot dot dot/g'
Lorem ipsum dot dot dot
Some dot dot dot more text

How to Replace or Add a String to a File Using sed

One way to do this it to bring grep into the equation. First check whether the file contains the string with a quick grep and then append or substitute accordingly:

grep -q string file && 
    sed -i 's/string/newstring/' file || echo "newstring" >> file

The above is a shorthand way of writing:

if grep -q string file; then 
    sed -i 's/string/newstring/' file
else
    echo "newstring" >> file
fi

Personally, however, I would use perl for this instead. Just read the file once and set a variable to 1 if the substitution was made. Then, at the end, add the string if the variable is not 1:

perl -lpe '$i=1 if s/oldstring/newstring/; 
           END{print "newstring" if $i!=1;}' file > tmpfile && mv tmpfile file

Best Answer

Related Solutions

Ubuntu – Replacing dots (.) in sed

How to Replace or Add a String to a File Using sed

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