The $ltrim operator removes leading characters from a string in MongoDB aggregation expressions. By default it strips whitespace from the left; optionally you can specify which characters to remove.
Start of string only.
input + optional chars.
Default trim behavior.
Strip prefixes like #.
Data cleaning, codes.
Left vs both sides.
In MongoDB’s aggregation framework, the $ltrim operator trims characters from the left side of a string. For example, " MongoDB" becomes "MongoDB" when you trim leading whitespace. This is useful when cleaning imported CSV data, normalizing product codes, or preparing strings for matching and display.
Think of $ltrim as MongoDB’s pipeline version of trimming only the start of a string — similar in spirit to JavaScript’s String.prototype.trimStart(), with an optional custom character set.
$ltrim only affects the left end. Trailing spaces stay in place. Use $trim to clean both sides, or $rtrim for the right end only.
The $ltrim operator takes an object with input and an optional chars field:
{
$ltrim: {
input: <expression>,
chars: <optional string>
}
}// Trim leading whitespace (default)
{ $ltrim: { input: "$name" } }
// Trim specific leading characters
{ $ltrim: {
input: "$code",
chars: "#0"
}}
// Trim a literal string
{ $ltrim: { input: " hello" } }input — required; the string expression to trim (field reference or literal).chars — optional; characters to remove from the left. If omitted, whitespace is trimmed.input is null, the result is null.$project, $addFields, or $set." hello " + $ltrim → "hello "" hello " + $rtrim → " hello"" hello " + $trim → "hello"$ltrim| Question | Answer |
|---|---|
| Operator type | Aggregation expression operator (string) |
| Syntax | { $ltrim: { input: ..., chars: ... } } |
| Default behavior | Remove leading Unicode whitespace |
| Custom trim | Pass chars with characters to strip |
| Common stages | $project, $addFields, $set |
{
$ltrim: {
input: "$name"
}
}Default left trim
{
$ltrim: {
input: "$code",
chars: "#"
}
}Strip # prefix
{
$ltrim: {
input: " hi"
}
}Returns "hi"
{
$ltrim: {
input: null
}
}Returns null
Walk through a products collection with messy string fields and clean leading characters with $ltrim.
Remove leading whitespace from imported product names using $project.
Suppose you have a products collection with untrimmed name and sku fields:
[
{ "_id": ObjectId("609c26812e9274a86871bc6a"), "name": " Notebook", "sku": "###NB-001" },
{ "_id": ObjectId("609c26812e9274a86871bc6b"), "name": "\tPen Pack", "sku": "##PP-002" },
{ "_id": ObjectId("609c26812e9274a86871bc6c"), "name": " Stapler", "sku": "#ST-003" }
]Trim spaces and tabs from the start of each product name:
db.products.aggregate([
{
$project: {
name: 1,
cleanName: {
$ltrim: { input: "$name" }
}
}
}
])chars, MongoDB removes leading whitespace (spaces, tabs, etc.).Strip specific prefix characters like # from SKU codes.
Remove leading # characters from SKU values:
db.products.aggregate([
{
$project: {
sku: 1,
cleanSku: {
$ltrim: {
input: "$sku",
chars: "#"
}
}
}
}
])The chars argument defines which characters to strip from the left. MongoDB removes them one by one from the start until it hits a character not in the set (like N or P).
Apply $ltrim to multiple fields in a single $addFields stage:
db.products.aggregate([
{
$addFields: {
name: {
$ltrim: { input: "$name" }
},
sku: {
$ltrim: {
input: "$sku",
chars: "#"
}
}
}
}
])$addFields overwrites the existing fields with cleaned values. Use this when you want to normalize data in place before downstream stages.
Trim a fixed string inside an expression:
db.products.aggregate([
{
$project: {
demo: {
$ltrim: { input: " MongoDB" }
}
}
}
])The input can be a literal string, not just a field path. Useful inside nested expressions and for testing trim logic.
When both leading and trailing whitespace matter, use $trim instead:
db.products.aggregate([
{
$project: {
name: 1,
fullyClean: {
$trim: { input: "$name" }
},
leftOnly: {
$ltrim: { input: "$name" }
}
}
}
])
// name: " Notebook "
// fullyClean → "Notebook" ($trim both sides)
// leftOnly → "Notebook " ($ltrim start only)Choose the right trim operator for your data. $ltrim is precise when you only need to fix the start of a string.
# or 0 from identifiers.$project for reports and APIs." active" matches "active" on the left side.$ltrim WorksThe input expression resolves to a string from a field or literal.
Uses chars if provided; otherwise defaults to Unicode whitespace.
Strips matching characters from the start until the first non-matching character.
The expression returns the string with leading characters removed.
The $ltrim operator is a practical string-cleaning tool for MongoDB aggregation pipelines. Use it to remove leading whitespace or custom prefix characters from field values before display, matching, or further string operations.
Remember: input is required, chars is optional, and only the left side is affected. For full whitespace cleanup on both ends, use $trim.
$ltrim when only leading characters need removalchars for standard whitespace cleanupchars to strip known prefix symbols like #$addFields before matching or grouping$trim when both ends need cleaning$ltrim to remove trailing spaces (use $rtrim or $trim)$ltrim as a pipeline stage — it is an expression operatornull input returns nullchars with a single prefix string — it is a character set$toString first if needed$ltrimUse these points when cleaning strings in MongoDB.
Start of string.
PurposeField or literal.
SyntaxCustom strip set.
OptionsLeft vs both.
CompareImports & SKUs.
Use caseMove on to $map for transforming array elements, or review $concat for joining strings.
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