I am trying to execute the following command from bash shell:

sed -i "s/\(update.*\)where /\1 where primary_id = '$primary_id', /" *.php

As you see, there is a variable which I am inserting using sed -- i.e. '$primary_id'. After executing the command, I see that the ''s are displayed, however $primary_id is missing.

How can I handle special characters, such as '?

closed as unclear what you're asking by roaima, vonbrand, dr01, jimmij, Scott Jan 4 '16 at 13:06

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 2
    Where's the output? – tjt263 Jan 4 '16 at 7:30
  • Those quote marks are being included because that's what your sed command has been instructed to do. Has $primary_id been given a value at the point the sed is run? Or are you wanting the literal '$primary_id' to be inserted into your PHP files? Please edit your question to make this clear. – roaima Jan 4 '16 at 10:29
  • What is unclear about this question? It is precisely the issue I face, and I understood the OP as it is currently written/edited. I do not think it should be closed. I don't have the Cast Close And Reopen Votes privs as I do on stackoverflow to vote to reopen here on stackexchange. – broc.seib Sep 1 '17 at 2:07

Let's make this a bit simpler. You want to replace every occurence of a with '$b' (a dollar, a b enclosed in single quotes). c, what the variable $b happens expands to, is not what you want.

sed -i "s/a/'$b'/g" *.php

The above command is similar to what you are doing in your problem. Because the string s/a/'$b'/g is enclosed in double quotes, variables are expanded, and the replacement string is 'c'.

If the whole sed command is enclosed in double quotes, you need to escape $. This is one solution:

sed -i "s/a/'\$b'/g" *.php\

Another possibility is to quote nothing, except for any character that has a spedcial meaning to the shell (not recommended, but it might be insightful):

sed -i s/a/\'\$b\'/g *.php
  • Why the downvote? It's a perfectly reasonable assumption of requirements from the unclear question, and clearly explains those assumptions up front. +1 from me – roaima Jan 4 '16 at 10:30
  • 1
    @roaima, it could be because of the sed -i 's/a/\'$b\'/g' *.php one which would only work with the fish shell. – Stéphane Chazelas Jan 4 '16 at 10:37
  • @StéphaneChazelas possibly, but references to fish and zsh are not at all uncommon on U&L (although they are generally flagged up explicitly so people don't assume they're bash code) – roaima Jan 4 '16 at 10:41
  • Assumptions, assumptions, assumptions. Thanks, @StéphaneChazelas, removed! – joepd Jan 4 '16 at 10:42
  • The last thing makes no sense. quote nothing except for any character that has a special meaning to the shell is all you ever can quote with shell quotes anyway. what do you think you're doing when you quote shell commands? sed "s/a/'$"b\'/g also works. – mikeserv Jan 8 '16 at 17:34

Unless I misunderstand, your command works exactly as expected:

$ cat test_file 
update name where a='b'
$ export primary_id="test"
$ sed -i "s/\(update.*\)where /\1 where primary_id = '$primary_id', /" test_file
$ cat test_file 
update name  where primary_id = 'test', a='b'

Special characters, preceded by \'s will be taken literally.
(Like you've done with your parentheses: (\( \))).

It should look like this: \'.
If you find that still doesnt work try: '\''.
Alternatively, try the hexadecimal escape sequence: \x27.

Also, regarding sed: Enclose your expression with:
Single Quotes ('s/1/2/g'). Not Doubles ("s/1/2/g").

sed -i 's/\(update.\*\)where /\1 where primary_id = \'$primary_id\', /' \*.php  

sed -i 's/\(update.\*\)where /\1 where primary_id = '\''$primary_id'\'', /' \*.php

sed -i 's/\(update.\*\)where /\1 where primary_id = \x27$primary_id\x27, /' \*.php
  • Why was this voted down? It's correct. – tjt263 Jan 4 '16 at 12:27
  • then why did you edit it? it's still basically incorrect even now, even it isn't just syntax error as before. ' is not a special character to sed - but is to the invoking shell. – mikeserv Jan 4 '16 at 15:08

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