LinuxQuestions.org - Handle escape characters in a string

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- - Handle escape characters in a string (https://www.linuxquestions.org/questions/programming-9/handle-escape-characters-in-a-string-176530/)

Handle escape characters in a string

echo -n "Please enter filename(s) in regular expression: "

read -r option # assume that the user typed in: .*\.txt
echo $option # prints out .*\.txt

How can I change the content of $option to be .*\\.txt?
Why can't I just do:
echo $option | tr '\' '\\' ?

I appreciate any help!
-Helene

Code:

#!/bin/bash

echo -n "Please enter filename(s) in regular expression: "

read -r option

echo $option | sed 's/\\/\\\\/'

Not sure what you're doing, but will that work? I tend not to use tr, but sed will do it if you escape the backslash and then escape both replacements.

Excellent, digiot! Now I'm soon ready to deliver my Uni assignment ;)

Uni assignment? Argh. I can usually tell when it's a homework thing, but I didn't realize it in this case. You do know you're not supposed to ask for homework help, right? I mean, you can ask about principles and I or others would offer hints and principles, but just straight questions and answers are kind of a no-no.

Ah well, bit past the point now. Good luck with the classwork, anyway.

Well, I'm only asking about principles, digiot. I would never have asked for direct answers when doing assignments! :study: If you are still willing to help me, I have one more question:

test=`echo $option | sed 's/\\/\\\\/''`

This results in Unterminated `s' command. Why?
I did find another way aronud (not pretty), but I'm just curious :rolleyes:

Actually, what you posted has two single quotes, so gets 'unexpected EOF' for me, but

Code:

test=`echo $option | sed 's/\\/\\\\/'`

does get 'unterminated'.

The original 'backticks' method is treated differently and the newer way works:

Code:

test=$(echo $option | sed 's/\\/\\\\/')

Near as I can figure, the backtick method is resulting in the backslashes getting 'swallowed', and maybe the slashes being treated by sed as literal - so it's still waiting on a 'special' slash to terminate the substitution.

Code:

~

990>> echo `echo /\\/\\\\/`                                                  

//\/



~

991>> echo $(echo /\\/\\\\/)                                                  

/\/\\/

In the first, bash is passing to sed what looks like 'substitute nothing with a literal slash and...' whereas the second is 'replace a slash with two'. Now, what bash is passing to sed and what echo is outputting in 990/991 are two different things but I still think that's basically what's going on. Could well be wrong, though. It's not that I'm not willing to help, but I just don't really know.

Just out of curiosity, what was the way around? (If you don't want to say, that's okay. I, too, know the shame of ugly workarounds. :) )

This one seems to be fine! I didn't know/think of using $().
test=$(echo $option | sed 's/\\/\\\\/')

And yes, I had a typo. I didn't mean to write two single quotes, only one.

My ugly solution was to write the variable to a file, and write it back into a variable using awk...
echo $option | sed 's/\\/\\\\/' > tmpFile ..... :rolleyes:

Yeah, I try to avoid temp files but sometimes it does seem like the least troublesome route. :) Glad the other suits.