How to specify Output Data Destination and Format for a "babel" command?

"babel" command arguments and options are organized into 3 sections as shown in the following syntax to convert chemical data from input to output with specified options.

babel input_section output_section option_section

You use output_section to specify Output Data Destination and Format for a "babel" command. The output_section must be the second section of the "babel" command line.

The output_section contains to two optional parts to specify output data format and output data destination as shown in the following syntax:

babel input_section [-o output_format] [output_name] option_section

There are 2 ways to specify output data format:

Explicit Format Name - A pre-defined format name is specified after the "-o" option flag with or without a space " ".

Here are some examples of specifying input data formats explicitly:

-o sdf 
-osdf 
-o smiles 
-osmiles 
-o svg 
-osvg
...

Implicit Format Name - No "-o" option flag is specified. In this case, the output_name part is required. Open Babel will determine the output data format implicitly from file name extension of output_name.

For example, the following "babel" command uses "molecule.svg" as the output_name to determine the output data format as "svg". This command writes data to molecule.svg in "svg" format.

fyicenter$ babel molecule.sdf molecule.svg 

1 molecule converted
29 audit log messages 

There are 3 ways to specify output data destination:

File name of a single output file - In this case, the output data goes to the specified file.

For example, the following "babel" command uses "molecule.svg" as the output_section, which specifies a single file named "molecule.svg". This command converts the molecule data from molecule.sdf to molecule.svg.

fyicenter$ babel molecule.sdf molecule.svg 

1 molecule converted
29 audit log messages 

File name prefix and extension for multiple output files with the "-m" option. In this case, the output data goes to multiple files, one per molecule.

For example, the following "babel" command uses "multi_.svg" as the output_section. This command converts molecules from multi.sdf to multi_1.svg, multi_2.svg, ..., because of the "-m" option.

fyicenter$ babel multi.sdf multi_.svg -m 
3 molecules converted
3 files output. The first is multi_1.svg
87 audit log messages 

fyicenter$ ls -l multi_*.* 
-rw-r--r--  1 fyicenter  staff  7665 Apr 1 20:42 multi_1.svg
-rw-r--r--  1 fyicenter  staff  5439 Apr 1 20:42 multi_2.svg
-rw-r--r--  1 fyicenter  staff  5189 Apr 1 20:42 multi_3.svg

"stdout" stream - No output file is specified. In this case, the output data goes to the "stdin" stream, which could be the console screen, or data redirected to a command pipe. With no input file name, "babel" requires the "-o ..." option in the output_section to specify the output data type.

For example, the following "babel" command uses "-o smiles" as the output_section, which tells Open Babel to read "stdin" as SMILES data. This command reads chemical data from molecule.sdf and write to the screen in SMILES format

fyicenter$ babel molecule.sdf -o smiles 

O(C(=O)CCN1CC1)CC  20009
1 molecule converted
34 audit log messages 

⇒ "babel" Command - Use "-o ..." as Output Delimiter

⇐ "babel" Command - Input Data Source and Format

⇑ Understanding "babel" Command Line Syntax

⇑⇑ Open Babel Tutorials