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Re: Bash Manual section 6.7 Arrays should mention array append notation

From: Greg Wooledge
Subject: Re: Bash Manual section 6.7 Arrays should mention array append notation
Date: Thu, 24 Mar 2022 11:24:35 -0400

On Thu, Mar 24, 2022 at 11:12:25AM -0400, Zachary Santer wrote:
> I'm consulting the online manual
> <https://www.gnu.org/software/bash/manual/html_node/index.html>, so if
> you're looking for a version number, that would be 5.1.
> I just now looked at doc/bash.pdf in the git repo on Savannah. No info on
> appending is present under bash-5.2-testing or devel.

> > Talking about the lines with "+=", obviously. I only learned I could
> > do this when I found it in existing code.

If you search the man page for += you can find this paragraph:

       In the context where an assignment statement is assigning a value to  a
       shell variable or array index, the += operator can be used to append to
       or add to the variable's previous value.  This  includes  arguments  to
       builtin  commands  such  as  declare  that accept assignment statements
       (declaration commands).  When += is applied to a variable for which the
       integer attribute has been set, value is evaluated as an arithmetic ex‐
       pression and added to the variable's current value, which is also eval‐
       uated.   When += is applied to an array variable using compound assign‐
       ment (see Arrays below), the variable's value is not unset  (as  it  is
       when  using  =),  and new values are appended to the array beginning at
       one greater than the array's maximum  index  (for  indexed  arrays)  or
       added  as additional key-value pairs in an associative array.  When ap‐
       plied to a string-valued variable, value is expanded  and  appended  to
       the variable's value.

The manual is not meant to be a tutorial.  It's a reference.  Information
may be in a different place than you expected, because things are
typically not repeated more than once.  (The man page is already extremely
long, and repeating things would make it even bigger.)

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