On Sat, 24 Mar 2007 14:23:39 -0400 Chet Ramey <[EMAIL PROTECTED]> wrote:
> Mike Frysinger wrote: > > i'm trying to determine whether POSIX allows for utilizing of > > variables in simple commands that were defined earlier in the same > > command ... in other words, whether this snippet: > > unset A B > > A="moo" B="$A more" > > echo $A , $B > > should display moo twice or just once: > > As I read Posix, twice, as long as there are only assignment > statements in the command. Assignment statements preceding simple > commands are treated differently. I don't see that posix defines simple commands like that - an assignment _is_ a simple command: `A "simple command" is a sequence of optional variable assignments and redirections, in any sequence, optionally followed by words and redirections, terminated by a control operator.' which implies to me that: A=one B="$A two" is a simple command. The same section (that Mike referred to - http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_09_01) also explicitly says that variable assignments are "saved for processing in steps 3 and 4". Step 2 expands all words except variable assignments and redirections - my interpretation of "variable assignment" is the `A=' part of the statement; i.e. that the rhs of the assignment is expanded. Step 3 does the redirections and step 4 does the variable assignments. So if expansions are done before the assignments, any assignment referring to other variables that are assigned, should be expanded with the value before the assignment. Either way, I've yet to find a shell that claims posix-compliance that does it the bash way; all of Solaris sh, BSD sh/ash/dash (not sure if Solaris is BSD or SYSV - or indeed if there's any difference) and busybox all yield "moo , more" in Mike's example. Hmm: $ A=one B="$A two" env A=one B= two ... $ A=one B="$A two" env | grep ^[AB]= A=one B=one two $ cat show_ab #!/bin/bash echo A: $A echo B: $B $ A=one B="$A two" ./show_ab A: one B: two $ A=one B="$A two" ./show_ab | more A: one B: one two is a little bizarre. Again; the other shells never yield "one two". -- Kevin F. Quinn
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