grep with multiple $

Question

I am grepping some php code files for an array variable and I ran into an issue which I am curious to understand.

I attempted to grep:

grep -RF "$array_variable['some_key'][$key_variable]" *

and it returned nothing. However, if I escape the second dollar sign, it then finds lines with that pattern.

grep -RF "$array_variable['some_key'][\$key_variable]" *

The -F flag from the man page says it treats the pattern as a fixed string and not a regex. It seems to handle the first dollar sign only.

Please help me understand how grep is interpreting this command. Could this be a shell issue rather than a regex issue?

UPDATE Added an additional array layer, which shows why I don't want to use single quotes. It's more work to escape the single quotes than the dollar sign.

See: [Difference between single and double quotes in bash](http://stackoverflow.com/q/6697753/3776858) — Cyrus, Sep 25 '17 at 18:10
I think first $ is being taken as a "start of line" anchor instead of a literal $. — Matias Barrios, Sep 25 '17 at 18:13
What did you intend `"$array_variable['some_key'][$key_variable]"` to mean? [edit] your question to include concise, testable sample input (including the values of any variables) and expected output and then someone will be able to help you. — Ed Morton, Sep 25 '17 at 19:16

anubhava · Accepted Answer · 2017-09-25T18:18:31.693

2

Use single quotes instead of double quotes. Double quotes let shell expand variable names starting with $:

grep -RF '$array_variable[$key_variable]' .

For your edited question, you can use escaped $ within double quotes:

grep -RF "\$array_variable['some_key'][\$key_variable]" .

edited Sep 25 '17 at 18:18

answered Sep 25 '17 at 18:10

anubhava

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Also, the shell is not expanding the $array_variable variable – Scott Joudry Sep 25 '17 at 18:13
Shell expands `$array_variable` as well and it expands to an empty string. But with escaped 2nd `$` it effectively becomes `grep -RF '[$key_variable]' .` and you get the result. When both variables expand then it effectively becomes `grep -RF '[]' .` and nothing is found. – anubhava Sep 25 '17 at 18:16

score 0 · Answer 2 · answered Sep 26 '17 at 04:23

I think you intend to search for occurrences of some array variable with two subindices values and you don't know that the square brackets are special for grep, meaning a class of characters. If you want to substitute the ${array_variable} name and ${key_variable} values into the grep expressión, you had better to use complete syntax as I have done, but the most important thing is that if you want to match literally the [ and ] brackets, you need to escape them. As in

grep -RF "${array_variable}\['some_key']\[${key_variable}]"

(only the left square bracket is needed to be escaped) In that case, if you have, for example foo stored in array_variable and bar in variable key_variable, the actual grep command will be

greep -RF "foo\['some_key']\[bar]"

withoug the escaping to the brackets, the regexp will search for occurences of foo, followed by one of 'somk_y and followed by one of bar, like foo'r, or foo__, but nothing similar to an array variable with its subindices.

grep with multiple $

2 Answers2