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$trim (aggregation)![](/docs/v4.4/assets/link.svg)
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Definition![](/docs/v4.4/assets/link.svg)
$trim
Removes whitespace characters, including null, or the specified characters from the beginning and end of a string.
$trim
has the following syntax:{ $trim: { input: <string>, chars: <string> } } The
$trim
takes a document with the following fields:FieldDescriptioninput
The string to trim. The argument can be any valid expression that resolves to a string. For more information on expressions, see Expressions.chars
Optional. The character(s) to trim from
input
.The argument can be any valid expression that resolves to a string. The
$trim
operator breaks down the string into individual UTF code point to trim frominput
.If unspecified,
$trim
removes whitespace characters, including the null character. For the list of whitespace characters, see Whitespace Characters.
Behavior![](/docs/v4.4/assets/link.svg)
By default,
$trim
removes whitespace characters, including the null character:ExampleResults{ $trim: { input: " \n good bye \t " } }
"good bye"
You can override the default characters to trim using the
chars
field.For example, the following trims any
g
ande
from the start and end of the input. Since the input starts with a whitespace, neither character can be trimmed from the start of the string.ExampleResults{ $trim: { input: " ggggoodbyeeeee", chars: "ge" } }
" ggggoodby"
If overriding the default characters to trim, you can explicitly include the whitespace character(s) to trim in the
chars
field.For example, the following trims any space,
g
,e
from the start and end of the input.ExampleResults{ $trim: { input: " ggggoodbyeeeee", chars: " ge" } }
"oodby"
Whitespace Characters![](/docs/v4.4/assets/link.svg)
By default, $trim
removes the following whitespaces,
including the null character:
Unicode | Escape sequence | Description |
---|---|---|
U+0000 | '0' | Null character |
U+0020 | ' ' | Space |
U+0009 | 't' | Horizontal tab |
U+000A | 'n' | Line feed/new line |
U+000B | 'v' | Vertical tab |
U+000C | 'f' | Form feed |
U+000D | 'r' | Carriage return |
U+00A0 | Non-breaking space | |
U+1680 | Ogham space mark | |
U+2000 | En quad | |
U+2001 | Em quad | |
U+2002 | En space | |
U+2003 | Em space | |
U+2004 | Three-per-em space | |
U+2005 | Four-per-em space | |
U+2006 | Six-per-em space | |
U+2007 | Figure space | |
U+2008 | Punctuation space | |
U+2009 | Thin space | |
U+200A | Hair space |
Example![](/docs/v4.4/assets/link.svg)
Consider an inventory
collection with the following documents:
{ "_id" : 1, "item" : "ABC1", quarter: "13Q1", "description" : " product 1" } { "_id" : 2, "item" : "ABC2", quarter: "13Q4", "description" : "product 2 \n The product is in stock. \n\n " } { "_id" : 3, "item" : "XYZ1", quarter: "14Q2", "description" : null }
The following operation uses the $trim
operator to remove
leading and trailing whitespaces from the description
field:
db.inventory.aggregate([ { $project: { item: 1, description: { $trim: { input: "$description" } } } } ])
The operation returns the following results:
{ "_id" : 1, "item" : "ABC1", "description" : "product 1" } { "_id" : 3, "item" : "XYZ1", "description" : null } { "_id" : 2, "item" : "ABC2", "description" : "product 2 \n The product is in stock." }