grep syntax for searching strings with single-quotes?

Question

So, I have a .js file as below and I am trying to search with the below grep pattern. I am not sure what mistake I did but it does not give any output even though the file has that pattern. What mistake am I doing and how to correct it?

.js file:

var View = require('ampersand-view');
window.jQuery = require('jquery');
require('bootstrap');
require('bootstrap-tooltip');
var extend = require('lodash/assign');

my requirement is to find any occurrences of: require('query')

grep I am using: grep 'require('jquery')' index.js

Answer 1

Single quotes cannot be embedded in single-quoted strings. Try:

$ grep "require('jquery')" index.js
window.jQuery = require('jquery');

Alternatively, you can end the single-quoted string, add an escaped single-quote, and then restart the single-quoted string:

$ grep 'require('\''jquery'\'')' index.js
window.jQuery = require('jquery');

Discussion

To understand better what is happening, you can use echo statements to see how the shell processes strings:

$ echo 'require('jquery')'
require(jquery)

In the above example, there are two single-quoted strings: require( and ). As far as the shell is concerned, the string jquery is unquoted.

$ echo "require('jquery')"
require('jquery')

Because the shell accepts single-quotes as part of double-quoted strings, the above works fine.

Sometimes, to avoid shell expansions, one needs everything to be in a single-quoted string. In that case:

$ echo 'require('\''jquery'\'')'
require('jquery')

In the above, there are three single-quoted strings: require(, jquery, and ). In between those strings are single-quotes that are escaped so that the shell treats them as normal characters.

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This answer assumes that the shell is bash, dash, ash, or other POSIX or bourne-derived shell. For information on still other shells, see Stéphane Chazelas' answer.

Answer 2

Single quotes can not be nested, use double quotes around the pattern:

grep "require('jquery')" file.js

When you do:

grep 'require('jquery')' file.js

The shell is first breaking the pattern into 3 parts, based on the single quotes. First Literal 'require(', then jquery, and then literal ')'. So in effect the pattern is taken as require(jquery), which is not matching anything expectedly.

Example:

$ cat foo.js 
var View = require('ampersand-view');
window.jQuery = require('jquery');
require('bootstrap');
require('bootstrap-tooltip');
var extend = require('lodash/assign');

$ grep "require('jquery')" foo.js
window.jQuery = require('jquery');

Answer 3

In most shells, the ' character is a quoting operator and the space character is used to separate arguments to a command. So your shell will parse that command as 3 arguments to pass to the /bin/grep command:

1. grep
2. require(jquery)
3. index.js

In 2 above, the 'require('jquery')' has been taken as a quoted require( concatenated with an unquoted jquery concatenated with a quoted ).

You want 2 to be require('jquery'). Since ', like ( and ) is special character to the shell, you need to quote it in some way. The syntax depends on the shell. In Bourne-like shells, fish and (t)csh, you can use double-quote which they recognise as another quoting operator:

 grep "require('jquery')"

In rc-like shells (rc, akanga, es) where '...' is the only form of quoting, the syntax is:

 grep 'require(''jquery'')'

That double-' within '...' is the rc way to escape a ' there.

For details on the special characters in the various Unix shells and how to quote/escape them, see How to use a special character as a normal one?.

Answer 4

Put the search pattern in double quotes.

grep "require('jquery')" index.js