I have a text file where I'd like to add a string in the beginning of the line, however, it has special characters and sed complains about that.

The warning I get is:

sed: 1: "s/^/curl curliian.bxss ...": bad flag in substitute command: 'b'

So I tried to escape the dot:

dirnamer="$(dirname $1 | sed 's/\./\\./g')"

Which didn't work, so I tried to escape the b, which didn't work either. So yeah, this is what I do right now:

sed -i '' "s/^/curl $dirnamer/g" ~/desktop/download

But it seems there's alot of problems to do with with sed, because of special characters. What's a better method?

  • when sed complains about b being a bad flag its not talking about the one following that .. its talking about s/^/replace/gpb where gpb are substitution flags and b is not valid. but you can just do: sed "i\\n$b" - though you might lose any backslashes in $b if you dont double them up, and if $b contains newlines you'll need to backslash escape those, too.
    – mikeserv
    Dec 7, 2015 at 12:46
  • I know, but I am was not using a b flag. Dec 7, 2015 at 12:47
  • well, you were. somewhere in your variable is /b
    – mikeserv
    Dec 7, 2015 at 12:47
  • @mikeserv That's correct, I should have edited the variable to escape that too. Dec 7, 2015 at 12:49
  • Please show us your actual input and the sed command you used. We can't tell you what you need to escape if we don't know what you're doing.
    – terdon
    Dec 7, 2015 at 12:55

1 Answer 1


This awk command works fine.

awk '{print "curl $dirnamer|" $0;}'

Or doing this to the variable before:

sed 's/\/b/\\b/g' | sed 's/\/t/\\t/g'
  • 1
    dont bother looking for [bt] - the problem is / in both cases. s/[\/]/\\&/g' is good enough for a substitution field of an s command with a / delimiter to handle any variable that doesnt contain a newline.
    – mikeserv
    Dec 7, 2015 at 13:00

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