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Zareh Kasparian avatar Server

whats the diffrence between "command.sh > /dev/null 2>&1" vs "command.sh 2>&1 >/dev/null"

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Zareh Kasparian

I have many shell and python scripts on my crontab that ending either with:

command.sh > /dev/null 2>&1

or

command.sh 2>&1 >/dev/null

I know that:

> is for redirect

/dev/null is a black hole where any data sent, will be discarded

2 is the file descriptor for Standard Error

> is for redirect

& is the symbol for file descriptor (without it, the following 1 would be considered a filename)

1 is the file descriptor for Standard Out

Therefore command.sh >/dev/null 2>&1 redirects the output of my program to /dev/null. Include both the Standard Error and Standard Out.

both have the same result and work fine, but why do some use the first type and some use the other?

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Massimo avatar Server
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Massimo

The commands are performing two redirects:

  • > /dev/null redirects Standard Output to /dev/null
  • 2>&1 redirects Standard Error to Standard Output

As you correctly guessed, the global effect is that both Standard Output and Standard Error are redirected to /dev/null.

The two redirects are both meant to be interpreted by the shell, not by the actual program called; thus they are appended to the end of the command line. They are logically distinct, although their effects are cumulative; thus they can be specified in any order you prefer.

TL;DR: the two commands are completely equivalent, the difference is purely cosmetical.

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