Base64: Encode and Decode Base64 Files

This page describes, in Unix manual page style, a program available for downloading from this site which encodes binary files in the “Base64” format used by MIME-encoded documents such as electronic mail messages with embedded images and audio files.


base64 - encode and decode base64 files


base64 [ -d / -e ] [ options ] [ infile ] [ outfile ]


The MIME (Multipurpose Internet Mail Extensions) specification (RFC 1341 and successors) defines a mechanism for encoding arbitrary binary information for transmission by electronic mail. Triplets of 8-bit octets are encoded as groups of four characters, each representing 6 bits of the source 24 bits. Only characters present in all variants of ASCII and EBCDIC are used, avoiding incompatibilities in other forms of encoding such as uuencode/uudecode.

base64 is a command line utility which encodes and decodes files in this format. It can be used within a pipeline as an encoding or decoding filter, and is most commonly used in this manner as part of an automated mail processing system.


Print copyright information.
-d, --decode
Decodes the input, previously created by base64, to recover the original input file.
-e, --encode
Encodes the input into an output text file containing its base64 encoding.
-n, --noerrcheck
Suppress error checking when decoding. By default, upon encountering a non white space character which does not belong to the base64 set, or discovering the input file is incorrectly padded to a multiple of four characters, base64 issues an error message and terminates processing with exit status 1. The -n option suppresses even this rudimentary error checking; invalid characters are silently ignored and the output truncated to the last three valid octets if the input is incorrectly padded.
-u, --help
Print how to call information and a summary of options.
Print program version information.


base64 returns status 0 if processing was completed without errors, 1 if an I/O error occurred or errors were detected in decoding a file which indicate it is incorrect or incomplete, and 2 if processing could not be performed at all due, for example, to a nonexistent input file.


If no infile is specified or infile is a single “-”, base64 reads from standard input; if no outfile is given, or outfile is a single “-”, output is sent to standard output. The input and output are processed strictly serially; consequently base64 may be used in pipelines.


Little or no error checking is done when decoding, other than validating that the input consists of a multiple of four characters in the encoding set. This is inherent in the design of base64, which assumes transmission integrity is the responsibility of a higher-level protocol.


uudecode(1), uuencode(1), RFC 1341

Download base64-1.5.tar.gz (Gzipped TAR archive)

The archive contains source code for the utility, a Makefile for Unix systems, and a ready-to-run executable for 32-bit Windows platforms. Windows users may also download, a ZIPped archive containing the Windows executable.

Read base64 source code (requires Acrobat Reader)


John Walker

Christian Ferrari contributed code which permits the base64 utility to work on EBCDIC based systems such as UNIX Services for OS/390 2.7 (ESA/390).

This software is in the public domain. Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, without any conditions or restrictions. This software is provided “as is” without express or implied warranty.

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by John Walker
June 10th, 2007
Version 1.5
The latest version of this program is available from: