what does '-' stand for in bash?

What exactly are the uses of '-' in bash? I know they can be used for

1. cd - # to take you to the old 'present working directory'
2. some stream generating com开发者_如何学运维mand | vim - # somehow vim gets the text.

My question is what exactly is - in bash? In what other contexts can I use it?

Regards Arun

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That depends on the application.

cd -

returns to the last directory you were in.

Often - stands for stdin or stdout. For example:

xmllint -

does not check an XML file but checks the XML on stdin. Sample:

xmllint - <<EOF
<root/>
EOF

The same is true for cat:

cat -

reads from stdin. A last sample where - stands for stdout:

wget -O- http://google.com

will receive google.com by HTTP and send it on stdout.

By the way: That has nothing to do with your shell (e.g. bash). It's only semantics of the called application.

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- in bash has no meaning as a standalone argument (I would not go as far as to say it it does not have a meaning in shell at all - it's for example used in expansion, e.g. ls [0-9]* lists all files starting with a digit).

As far as being a standalone parameter value, bash will do absolutely nothing special with it and pass to a command as-is.

What the command does with it is up to each individual program - can be pretty much anything.

There's a commonly used convention that - argument indicates to a program that the input needs to be read from STDIN instead of a file. Again, this is merely how many programs are coded and technically has nothing to do with bash.

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From tldp:

This can be done for instance using a hyphen (-) to indicate that a program should read from a pipe

This explains how your vim example gets its data.

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There is no universal rule here.

According to the context it changes

1. It is pretty much useful when you have something to do repeatedly in two directories. Refer #4 here: http://www.thegeekstuff.com/2008/10/6-awesome-linux-cd-command-hacks-productivity-tip3-for-geeks/

2. In many places it means STDIN.