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111 lines
2.7 KiB
Markdown
111 lines
2.7 KiB
Markdown
# Tilde expansion
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~
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~/...
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~NAME
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~NAME/...
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~+
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~+/...
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~-
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~-/...
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The tilde expansion is used to expand to several specific pathnames:
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- home directories
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- current working directory
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- previous working directory
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Tilde expansion is only performed, when the tilde-construct is at the
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beginning of a word, or a separate word.
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If there's nothing to expand, i.e., in case of a wrong username or any
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other error condition, the tilde construct is not replaced, it stays
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what it is.
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Tilde expansion is also performed everytime a variable is assigned:
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- after the **first** `=`: `TARGET=~moonman/share`
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- after **every** `:` (colon) in the assigned value:
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`TARGET=file:~moonman/share`
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\<note info\> As of now (Bash 4.3-alpha) the following constructs
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**also** works, though it's not a variable assignment:
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echo foo=~
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echo foo=:~
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I don't know yet, if this is a bug or intended. \</note\>
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This way you can correctly use the tilde expansion in your
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[PATH](../../syntax/shellvars.md#PATH):
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PATH=~/mybins:~peter/mybins:$PATH
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**Spaces in the referenced pathes?** A construct like\...
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~/"my directory"
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\...is perfectly valid and works!
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## Home directory
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~
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~<NAME>
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This form expands to the home-directory of the current user (`~`) or the
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home directory of the given user (`~<NAME>`).
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If the given user doesn't exist (or if his home directory isn't
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determinable, for some reason), it doesn't expand to something else, it
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stays what it is. The requested home directory is found by asking the
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operating system for the associated home directory for `<NAME>`.
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To find the home directory of the current user (`~`), Bash has a
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precedence:
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- expand to the value of [HOME](../../syntax/shellvars.md#HOME) if it's
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defined
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- expand to the home directory of the user executing the shell
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(operating system)
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That means, the variable `HOME` can override the \"real\" home
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directory, at least regarding tilde expansion.
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## Current working directory
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~+
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This expands to the value of the [PWD](../../syntax/shellvars.md#PWD) variable,
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which holds the currect working directory:
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echo "CWD is $PWD"
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is equivalent to (note it **must** be a separate word!):
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echo "CWD is" ~+
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## Previous working directory
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~-
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This expands to the value of the [OLDPWD](../../syntax/shellvars.md#OLDPWD)
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variable, which holds the previous working directory (the one before the
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last `cd`). If `OLDPWD` is unset (never changed the directory), it is
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not expanded.
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$ pwd
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/home/bash
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$ cd /etc
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$ echo ~-
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/home/bash
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## See also
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- Internal: [Introduction to expansion and
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substitution](../../syntax/expansion/intro.md)
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