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I noticed an example from https://unix.stackexchange.com/a/383825/674

$ alias foo=bar $ foo () { blah "$@"; } $ type -a foo bar foo is aliased to `bar' bar is a function bar () { blah "$@" }

So redefining the alias foo actually redefines the aliased command bar. This works like a nameref, i.e. a variable with the reference attribute.

I experimented more with the following examples.

  • Why does mya=cat not re-alias mya to cat, nor redefines the aliased echo to cat?

  • Why does mya () { cat test.sh; } redefine the aliased echo to the function, just like a nameref?

Thanks.

$ alias mya=echo $ type mya mya is aliased to `echo' $ mya abc # mya behaves exactly as echo abc $ mya=cat $ type mya mya is aliased to `echo' $ mya test.sh # mya=cat doesn't alias mya to cat test.sh $ mya () { cat test.sh; } $ type mya mya is aliased to `echo' $ mya # Redefining mya as a function works, by outputing the content of test.sh #! /usr/bin/env bash echo $_ echo $0 $ echo # Redefining mya also redefines the aliased echo, just like a nameref #! /usr/bin/env bash echo $_ echo $0
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  • mya=cat defines a variable, not an alias. You'd have to use $mya to access the variable's value. Commented Aug 4, 2017 at 16:04
  • And another data point for you: alias foo=bar; function foo () { echo booh } → The alias foo shadows the function foo (like it would for normal programs, see the ubiquitous alias rm='rm -i'), but as usual you can circumvent the alias by calling \foo. Commented Aug 4, 2017 at 16:07

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An alias is expanded when it's the first word in the command. So when you type:

alias foo=bar foo () { blah "$@"; }

the alias foo is expanded, so it's treated as if you'd typed:

bar () { blah "$@"; }

When you type:

alias mya=echo mya=cat

the first word in the command is mya=cat, not just mya, so the alias is not expanded. = is not a word delimiter, it's merely the delimiter between the variable and value in a variable assignment.

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  • Thanks. How can i realias an existing alias to a different command, since assignment doesn't do the work? Commented Aug 5, 2017 at 10:00
  • Just do another alias command. alias mya=cat Commented Aug 5, 2017 at 16:23
  • Variable assignment is not subject to alias substitution, but this is not because the first word of the command is mya=cat. The first word of the command is what follows all variable assignments (in your example there is none). Therefore mya=cat foo=bar mya ... would execute echo ... Commented Aug 6, 2017 at 1:14
  • @xhienne True, that's another way to explain it. What I find somewhat confusing is that alias substitution is only supposed to happen in simple commands. Is a function definition a simple command? Yet it's happening there. Commented Aug 6, 2017 at 1:27
  • Each compound command is split in simple commands. Each first word of those simple commands is subject to alias substitution. A function is a compound command. Commented Aug 6, 2017 at 2:01

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