Using sed to replace words in a file

So there’s actually a story behind this 😆

My conkyrc file has grown to a fairly large size and it’s a bit of a pain to go through it to change the colors. After all there’s lots of ${color} in it 😆

So I needed a command that could do this for me. That’s when I found sed, a stream editor. sed can replace a word or set of words with a different word or set of words.

There’s a couple different ways to use sed. You can have it replace only the first instance of a word in a sentence or you can have it replace the word globally.

To replace only the first instance of a word in a sentence the command looks like this

sed -i ‘s/original_word/new_word/’ file.txt

To change all instances of a word in a file the command is

sed -i ‘s/original_word/new_word/g’ file.txt

the “g” at the end tells sed to perform the action globally.

You can also do more than one word, like a phrase. To do this correctly you need to use a “\” backslash before the space. So for example I wanted to replace all instances of “black” with “light blue” in my conkyrc. This is what the command looked like

sed -i ‘s/black/light\ blue/g’ .conkyrc

That saved me about 5 minutes of editing my conkyrc.

So there you have it, a very useful time saving command.

Or you can use the Replace button in Gedit which somehow I managed to overlook while trying to figure out a command to do this! 😳 😯 😆

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15 thoughts on “Using sed to replace words in a file”

  1. That’s a good one to remember.

    I use a different technique in the .conkyrc though. Instead of using hex numbers like FF6600 in the color tags, I have color declarations just before the TEXT part.

    E.g. I could have:
    color1 447788
    color2 110099
    color3 334477

    And then under the TEXT part, instead of using ${color 447788} to change to the color I want, I just use ${color1} instead (or you can leave out the brackets). Then, when you go through and want to change colors, you can just do it at the top. 🙂

    Anyway that’s my way of doing it, but using sed seems just as good 😛

  2. How do I replace only if the keyword is at the begining of a line?

    Code:
    —-
    a = “This is a print statement”
    print(a)
    —-
    What if I want to replace print by #print only in the second line i.e only if the line starts with that keyword.

    Please help me out. I’m new to SED.


  3. but you really need to get used to regexps
    at least enough to understand what’s the difference between
    “s/^print/replacement/”
    and
    “s/^ *print/replacement/”

  4. For reference, the space does not need to be “escaped” by the slash, since the entire sed command is already in single quotes.

  5. hi all,
    i have some question i need ur help.

    i want to change a pattern in a files in a direcotry.

    i tried like this but it is able to modify only first file and saved in the temporary file.

    but i need it should change in same file and save it.

    my code is like this i am running this sed command in tcl script file it not not working but in unix it is wokring.

    foreach fl {atsim_1 atsim_2 atsim_3 atsim_4 atsim_5 atsim_6 hcssim_1 hcssim_2 hcssim_3 hcssim_4 hcssim_5 hcssim_6 pppmgr_1 pppmgr_2 pppmgr_3 pppmgr_4 pppmgr_5 pppmgr_6 hcsoam} {

    send -i $Id “chmod 755 $fl \r”
    send -i $Id “exec sed {s/R$srel/R$frel/g} $fl > tmp_file && mv -f tmp_file $fl \r”

    }

    please help me in resolving this problem.

    my mail id gopib.4180@gmail.com

    thanks,
    gopi

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