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📖 NAME

stdbuf — run a command with modified I/O stream buffering

🚀 Quick Reference

Use Case	Command	Description
🧵 Line buffer stdout	stdbuf -oL command	Set stdout to line-buffered mode
🔌 Disable buffering for stderr	stdbuf -e0 command	Make stderr unbuffered (immediate output)
📦 Specify buffer size for stdin	stdbuf -i 4M command	Set stdin buffer to 4 MiB
⚙️ Full buffering with custom size	stdbuf -o 8K command	Set stdout to fully buffered with 8KB buffer

📋 SYNOPSIS

stdbuf OPTION... COMMAND

Any additional ARGs are passed as additional arguments to COMMAND.

📝 DESCRIPTION

stdbuf allows one to modify the buffering operations of the three standard I/O streams (stdin, stdout, stderr) associated with a program.

COMMAND must start with the name of a program that:

• ✅ uses the ISO C FILE streams for input/output (note: dd and cat do not use these),
• ✅ does not adjust the buffering of its standard streams (note: tee is not in this category).

stdbuf is installed only on platforms that use the Executable and Linkable Format (ELF) and support the constructor attribute, so portable scripts should not rely on its existence.

⚙️ OPTIONS

• -i MODE, --input=MODE — 📥 Adjust the standard input stream buffering.
• -o MODE, --output=MODE — 📤 Adjust the standard output stream buffering.
• -e MODE, --error=MODE — ❌ Adjust the standard error stream buffering.

The MODE can be specified as follows:

• L — 🧵 Set the stream to line buffered mode. Data is coalesced until a newline is output or input is read from any stream attached to a terminal device. This option is invalid with standard input.
• 0 — 🔌 Disable buffering of the selected stream. Data is output immediately and only the amount of data requested is read from input. Note the difference in function for input and output. Disabling buffering for input will not influence the responsiveness or blocking behavior of the stream input functions. For example fread will still block until EOF or error, even if the underlying read returns less data than requested.
• SIZE — 📦 Specify the size of the buffer to use in fully buffered mode. SIZE may be, or may be an integer optionally followed by, one of the following multiplicative suffixes:

  KB =>           1000 (KiloBytes)
  K  =>           1024 (KibiBytes)
  MB =>      1000*1000 (MegaBytes)
  M  =>      1024*1024 (MebiBytes)
  GB => 1000*1000*1000 (GigaBytes)
  G  => 1024*1024*1024 (GibiBytes)

  and so on for T, P, E, Z, and Y. Binary prefixes can be used, too: KiB=K, MiB=M, and so on.

🚪 Exit Codes

• 125 — if stdbuf itself fails
• 126 — if COMMAND is found but cannot be invoked
• 127 — if COMMAND cannot be found
• 🔢 the exit status of COMMAND otherwise

📖 NAME 🚀 Quick Reference 📋 SYNOPSIS 📝 DESCRIPTION ⚙️ OPTIONS 🚪 Exit Codes