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How do I remove lines of a file (hosts) which contain "adf.ly" string?

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6 Answers 6

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13

using sed

Run this command:

sed -i '/adf\.ly/d' inputfile

man sed

   -i[SUFFIX], --in-place[=SUFFIX]
      edit files in place (makes backup if extension supplied)

Using grep

Thanks for @kos notes:

grep -v "ad\.fly" inputFile  > outputfile
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  • 2
    You're doing two different things in the sed and in the grep version: in the sed version you're deleting all the lines containing an ad.fly substring while in the grep version you're deleting only lines containing an ad.fly substring surrounded by a non-word character (i.e. not surrounded by [A-Za-z0-9_]); in the grep command also the . matches any character (i.e. it will exclude lines containing e.g. adxfly) and you're not using any of the EREs' syntax in the pattern, so the -E option is not really needed.
    – kos
    Jun 16, 2015 at 9:11
  • However I didn't downvote this, drop me a comment if you ever correct this and I'll upvote it since the sed version is fine
    – kos
    Jun 16, 2015 at 9:35
  • @kos Even you downvote it's legitimated :). I removed the grep for now
    – Maythux
    Jun 16, 2015 at 9:35
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    I will fix it before adding it again
    – Maythux
    Jun 16, 2015 at 9:39
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    +1 for grep, which is IMO the most straightforward way to do this.
    – Gaurav
    Jun 16, 2015 at 18:33
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The following will remove the lines containing "adf.ly" in filename.txt in-place:

sed -i '/adf\.ly/d' filename.txt

Use the above command without -i to test it before removing lines.

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3

Using awk (thanks to terdon for the shortened version):

< inputfile awk '!/adf\.ly/' > outputfile
  • < inputfile: redirects the content of inputfile to awk's stdin
  • > outputfile: redirects the content of awk's stdout to outputfile

awk command breakdown:

  • !/adf\.ly/: prints the record if not matching the adf\.ly regex

Using Perl (thanks to terdon for the shortened version):

< inputfile perl -ne '/adf\.ly/||print' > outputfile
  • -n: places a while (<>) {[...]} loop around the script
  • -e: reads the script from the arguments

Perl command breakdown:

  • /: starts the pattern
  • adf\.ly: matches an adf\.ly string
  • /stops the pattern
  • ||: executes the following command only if the pattern didn't match the line
  • print: prints the line
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    Why not just awk '!/ad\.fly/' in > out? You could also shorten the Perl to perl -ne '/ad\.fly/||print' file if you're into golfing :)
    – terdon
    Jun 16, 2015 at 12:03
  • @terdon Because I'm silly (awk) and anyway not that proficient in both languages. Thanks for your suggestions (by the way I didn't get the golfing reference!)
    – kos
    Jun 16, 2015 at 12:19
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    Code golfing is the game of making code as concise as possible, usually at the price of sacrificing legibility. My point is that the perl alternative I gave is indeed shorter but yours was much clearer and more understandable to a non-expert.
    – terdon
    Jun 16, 2015 at 13:11
  • @terdon Ah I see, yes I'd say I am then. After all it's sill explained right after
    – kos
    Jun 16, 2015 at 13:29
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Here is a bash one-liner:

while IFS= read -r i; do [[ ! $i =~ .*adf\.ly.* ]] && echo "$i"; done <file.txt

  • Variable i will contain each line while iterating

  • [[ $i =~ .*adf\.ly.* ]] checks if the line has the string adf.ly, ! negates the check so [[ ! $i =~ .*adf\.ly.* ]] will check if the line does not contain adf.ly

  • If yes (&&), then the line will be printed.

To save the output to another file (out.txt):

while IFS= read -r i; do [[ ! $i =~ .*adf\.ly.* ]] && echo "$i"; done <file.txt >out.txt
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    +1, just a little suggestion, you can directly pattern match against adf\.ly
    – kos
    Jun 16, 2015 at 12:47
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You could use the standard text editor, ed:

printf '%s\n' 'g/adf\.ly/d' w q | ed file.txt
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  • Great, a +1 for ed =)
    – A.B.
    Jun 16, 2015 at 17:50
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You can use Vim in Ex mode:

ex -sc 'g/adf\.ly/d' -cx hosts

  1. g global search

  2. d delete

  3. x save and close

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