#command-line-arguments #input-output #file-input #command-line-tool #file-io #utility #child-process

bin+lib o-o

Enables commands that assume the standard input and output to read and write to files specified in the command line

13 releases

0.4.5 Jan 25, 2023
0.4.4 Jan 24, 2023
0.4.3 Oct 4, 2022
0.3.6 Apr 3, 2022
0.2.3 Nov 25, 2021

#351 in Command line utilities


688 lines


Enables commands that assume the standard input and output to read and write to files specified in the command line.

What? Why?

Have you ever had trouble with interference between a command-invoking command and redirection?

For example, a command line:

ls *.txt | xargs -I {} head -n 3 {} > {}-head.out

does NOT create *-head.out file for each of the *.txt files but creates one file {}-head.out containing outputs of all head command executions.

The command o-o is here to help!

You can now run as follows:

ls *.txt | xargs -I {} o-o - {}-head.out - head -3 {}


The o-o arguments are the standard input, standard output, and standard error output of the child process, and the subsequent arguments are the command line to start the child process.

If you specify - as the file name for standard input, etc., it will not be redirected. Putting + in front of a file name will open the file in append mode.

Start a sub-process and redirect its standard I/O's.

  o-o [options] <stdin> <stdout> <stderr> [--] <commandline>...
  o-o --help
  o-o --version

  <stdin>       File served as the standard input. `-` for no redirection.
  <stdout>      File served as the standard output. `-` for no redirection. `=` for the same file as the standard input. `.` for /dev/null.
  <stderr>      File served as the standard error. `-` for no redirection. `=` for the same file as the standard output. `.` for /dev/null.
                Prefixing the file name with `+` will append to the file (`>>` in shell).
  -e VAR=VALUE                      Environment variables.
  --pipe=STR, -p STR                String for pipe to connect subprocesses (`|` in shell) [default: `I`].
  --separator=STR, -s STR           String for separator of command lines (`;` in shell) [default: `J`].
  --tempdir-placeholder=STR, -t STR     Placeholder string for temporary directory [default: `T`].
  --force-overwrite, -F             Overwrite the file even when exit status != 0. Valid only when <stdout> is `=`.
  --working-directory=DIR, -d DIR   Working directory.
  --version, -V                     Version info.
  --help, -h                        Help message.


Use the cargo command to install.

cargo install o-o


1. Extract the 5th line for each of PDF files

When you know that a particular line of the PDF will contain the information you need, such as the title of a artcle.

ls *.pdf | rargs o-o - - - pdftotext '{0}' - I head -5 I tail -1


  • rargs is a tool which takes a filename and executes the specified command line, similar to xargs
  • pdftotext is a tool to extract text from PDF file.

2. Extract vba source code from Excel files

For each of *.xlsm files, extract vba source code from it, delete the first 5 lines, and save the code to a file with the same name but with the extension changed to .vba.

ls *.xlsm | rargs -p '(.*)\.xlsm' o-o - '{1}'.vba - olevba -c '{0}' I sed -e 1,5d

The above executes the following command line when there was a file named foo.xlsm, for example.

olevba -c foo.xlsm | sed -e 1,5d > foo.vba


  • olevba is a command to extract vba code from an Excel file.

3. Transcribing audio from a video file

Extract the audio from the video file amovie.webm, save it to a temporary audio file, and then extract text from the temporary audio file. The temporary file is created on a temporary directory and deleted when the process is finished.

o-o - - - ffmpeg -i amovie.webm T/tmp.wav J whisper T/tmp.wav --model=medium

The above command line is similar to the following command line, except for creating a temporary directory.

ffmpeg -i amovie.webm tmp.wav ; whisper tmp.wav --model=medium


  • ffmpeg is a tool for processing audio files and video files.
  • whisper is a tool for transcribing text from audio files.




  • Reimplemented in Rust
  • Testing --force-overwrite
  • Enable handling of /dev/null
  • Temporary directory (v0.4.0)
  • Command-line separator (v0.4.0)


~141K SLoC