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Re: unexpected behavior with read


From: Chet Ramey
Subject: Re: unexpected behavior with read
Date: Sun, 4 Mar 2018 20:55:04 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 3/4/18 6:15 PM, Zach Hadgraft wrote:

> Bash Version: 4.4
> Patch Level: 19
> Release Status: release
> 
> Description:
>         global variable assignments fail when part of a sequence that
> includes read and begins with a function invoked by command substitution
>         read can be invoked by another function, or invoked by another
> command and the result is the same
> 
> Repeat-By:
> 
> """
> #!/bin/bash
> 
> 
> r=
> 
> f ()
> {
>     if [ -z "$r" ]; then
>         r="x"
>         read
>     fi
>     echo "$r"
> }
> 
> echo "$(f)"
> echo "$(f)"
> """

What do you expect to happen, and what happens instead? When I run this
script, the `read' gets satisfied when you enter a line of text followed
by a newline, and `x' is assigned to r:

line
x
line
x

Since command substitution happens in a subshell, and subshells can't
affect their parent's environment, `r' isn't going to change in the
calling shell.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/



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