Symbols Archive¶

A reference of special characters and their behavior across parsing contexts. This archive documents the exact interpretation of every symbol encountered in cmd.exe command processing, HTML attribute parsing, and Base64 encoding alphabets. The behavior documented here is derived from direct experimentation and verified against official specifications.

Overview¶

cmd.exe Control Characters¶

The following characters trigger special interpretation during cmd.exe command-line parsing. The parser operates in phases: first, the entire line (including parenthesized blocks) is read; second, variables are expanded; third, redirection operators are processed; finally, the command is executed.

flowchart LR
    subgraph Parse["Parse Phase"]
        P1["Variable<br/>Expansion<br/>%VAR%"]
        P2["Caret<br/>Escaping<br/>^char"]
        P3["Quote<br/>Toggle<br/>”"]
    end

    subgraph Execute["Execution Phase"]
        E1["&<br/>Command sep"]
        E2["|<br/>Pipe"]
        E3["< ><br/>Redirect"]
    end

    subgraph Effect["Effect"]
        direction TB
        SAFE["Literal-safe:<br/>Base64 encoding<br/>Delayed expansion<br/>FOR/F parsing"]
    end

    Parse --> Execute --> Effect

Quoting and Escaping Mechanics¶

Caret Escaping¶

The caret (^) is the general-purpose escape character in cmd.exe. It prevents the next character from being interpreted as a control operator.

REM Escaping redirection operators
echo This ^> that        REM Outputs: This > that
echo This ^& that        REM Outputs: This & that
echo This ^|^| that      REM Outputs: This || that

REM Escaping the escape character itself
echo Caret: ^^           REM Outputs: Caret: ^

REM Escaping in a variable assignment
set "expr=5 ^> 3"
echo %expr%              REM Outputs: 5 > 3

Quote Handling in FOR /F Delimiters¶

When specifying " as a delimiter in FOR /F, the parser's quote-toggle behavior creates a special case:

REM This uses escaped quotes within the options string
FOR /F "delims=^\"" %%A IN ('command') DO echo %%A

The "delims=^"" syntax works because the caret escapes the quote, preventing it from toggling parser state while still passing the quote character as the delimiter value.

Environment Variable Expansion¶

Immediate Expansion (%VAR%)¶

By default, variables are expanded when the line is parsed, not when it is executed. This means the value is fixed before any commands on that line run.

@echo off
set VAR=before
set VAR=after & echo %VAR%
REM Outputs: before (the old value, expanded before set executed)

Delayed Expansion (!VAR!)¶

Delayed expansion, enabled via SETLOCAL EnableDelayedExpansion or cmd /v:on, defers variable expansion until execution time. Variables enclosed in exclamation marks are re-evaluated each time they are encountered.

@echo off
SETLOCAL EnableDelayedExpansion
set VAR=before
set VAR=after & echo %VAR% !VAR!
REM Outputs: before after
REM %VAR% shows parse-time value; !VAR! shows execution-time value

FOR /F Parsing Modes¶

The FOR /F command processes command output or file content with configurable parsing behavior controlled by its options string.

Options Reference¶

usebackq Modes¶

FOR /F has three quote-handling modes determined by usebackq:

flowchart TD
    subgraph Default["Default Mode"]
        D1["'text'<br/>== LITERAL TEXT"]
        D2["ˋcommandˋ<br/>== COMMAND"]
    end

    subgraph Usebackq["usebackq Mode"]
        U1["'file.txt'<br/>== FILENAME"]
        U2["ˋcommandˋ<br/>== COMMAND"]
    end

    Default -->|"usebackq option"| Usebackq

REM Default mode: single-quoted strings are LITERAL TEXT
FOR /F "delims=" %%A IN ('literal text here') DO echo %%A
REM Processes the words "literal", "text", "here" as lines

REM usebackq mode: backquoted strings are COMMANDS
FOR /F "usebackq delims=" %%A IN (`dir /b`) DO echo %%A
REM Runs 'dir /b' and processes its output

REM usebackq mode: single-quoted strings are FILENAMES
FOR /F "usebackq delims=" %%A IN ('C:\path\to\file.txt') DO echo %%A
REM Reads lines from the specified file

HTML Encoding Characters¶

Characters that require encoding when appearing in HTML attribute values or text content.

Base64 Alphabet¶

RFC 4648 specifies the following character-to-value mapping for Base64 encoding:

The URL-safe variant (RFC 4648 section 5) substitutes - for + and _ for /, with padding omitted.

Path and Separator Characters¶

Related Pages¶

• Stereograms — 3D depth encoding in 2D images
• cmd.exe Literacy — Detailed parser phase documentation
• Base64 Encoding — Base64 encoding/decoding reference

Related Deep Hole¶

• Stack Overflow: How does delayed expansion work in a batch script? — Deep dive into the parse phases of cmd.exe
• Stack Overflow: Example of delayed expansion in batch file — Iteration counter example with and without delayed expansion
• SS64 Forum: SETLOCAL ENABLEDELAYEDEXPANSION discussion — Caret double-escaping behavior with delayed expansion enabled
• Server Fault: Double expansion syntax with delayed expansion — CALL statement as second expansion mechanism
• TenForums: Batch file issue with EnableDelayedExpansion — Common IF-block variable update confusion
• The Old New Thing: Environment variable expansion — Raymond Chen's explanation of parse-time vs execution-time expansion