Escaping a backslash in SED command in a shell script

Scripting Forums AppleScript | Mac OS X
#1

I use see quite often in shell scripts but have just run into an issue of escaping a backslash in a sed string:

If I don’t put a backslash in from of the “\a”, AS complains and won’t compile.
If I do put one to escape the “\a”, AS compiles but sed fails.

Can anyone tell me how I might work around this?

This works:

This fails to compile:

This compiles but causes a sed failure:

Error is (Script Debugger won’t display entire message):

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#2

Hi,

normally a second backslash is needed to escape the first one


do shell script "sed '/Sunrise/ a\\Add this line after every line with Sunrise'"

You could also try


set theText to "/Sunrise/ a\\Add this line after every line with Sunrise"
do shell script "sed " & quoted form of theText

quoted form of uses always the best way to escape the phrase

#3

Good suggestion. Here is what happens:

#4

please look at my example, quoted form of is not part of the literal string

#5

You’re right, I wasn’t careful.

Like this then?

#6

add a space character after sed

#7

Here’s what I get:

I’m beginning to wonder if I have the basic sed command wrong. I’ll dig into that.

#8

Hi.

The ‘a’ command should be followed by both an escaped backslash and a linefeed. And if you want to insert a line rather than just prepend it to the following one, the inserted text should be followed by a linefeed too. Assuming the first part of your shell script works OK, it would look like this:

set sunriseLines to do shell script "/usr/local/bin/tide -em p -tf \"%H:%M %Z\"   -l \"" & theTideStationChosen & "\" | sed '/Sunrise/ a\\'$'\\n''Add this line after every line with Sunrise'$'\\n'''"

Or slightly more simply:

set sunriseLines to do shell script "/usr/local/bin/tide -em p -tf \"%H:%M %Z\"   -l \"" & theTideStationChosen & "\" | sed '/Sunrise/ a\\\nAdd this line after every line with Sunrise\n"
#9

Brilliant Nigel, thank you. I have a lot more to learn about those *nix utilities!

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