Could somebody please tell me what's going on here?
First, here is a minimal example:
LINE|
0000| $ echo "$(echo '"' | awk '{sub(/a/,$0)}')"
0001| awk: cmd. line:1: sub(/a/
0002| awk: cmd. line:1: ^ unexpected newline or end of string
0003| awk: $0)
0004| awk: ^ syntax error
0005|
Where is this newline coming from? What happened to the comma?
Look what happens if we add the action `NR=1'; notice that the error
message seems to show that the `{' has been removed:
LINE|
0000| $ echo "$(echo '"' | awk 'NR==1 {sub(/a/,$0)}')"
0001| awk: cmd. line:1: NR==1 sub(/a/
0002| awk: cmd. line:1: ^ unexpected newline or end of string
0003| awk: NR==1 $0)
0004| awk: ^ syntax error
0005|
Interestingly, the whole thing seems to become syntactically correct
when I put a space between the `{' and the `sub' (and experimentation
shows that it is working):
LINE|
0000| $ echo "$(echo '"' | awk 'NR==1 { sub(/a/,$0)}')"
0001|
The problem also goes away when I just remove the outer quotes:
LINE|
0000| $ echo $(echo '"' | awk 'NR==1 {sub(/a/,$0)}')
0001|
However, it should be noted that the outer quotes should not have an
effect on any characters within the command substition `$(...)';
consider what the POSIX shell documentation here:
http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_02_03
says:
Enclosing characters in double-quotes ("") shall preserve the
literal value of all characters within the double-quotes, with
the exception of the characters dollar sign, backquote, and
backslash, as follows:
$
The dollar sign shall retain its special meaning
introducing parameter expansion (see Parameter
Expansion), a form of command substitution (see
Command Substitution), and arithmetic expansion
(see Arithmetic Expansion).
The input characters within the quoted string
that are also enclosed between "$(" and the
matching ')' shall not be affected by the
double-quotes, but rather shall define that
command whose output replaces the "$(...)" when
the word is expanded. The tokenizing rules in
Token Recognition , not including the alias
substitutions in Alias Substitution , shall be
applied recursively to find the matching ')'.
...
...
In particular:
The input characters within the quoted string
that are also enclosed between "$(" and the
matching ')' shall not be affected by the
double-quotes, but rather shall define that
command whose output replaces the "$(...)" when
the word is expanded.
>From what I can tell, bash follows the same semantics; the manual here:
$ info '(bash)Double Quotes'
or here:
http://www.gnu.org/software/bash/manual/html_node/Double-Quotes.html#Double-Quotes
says:
3.1.2.3 Double Quotes
.....................
Enclosing characters in double quotes (`"') preserves the
literal value of all characters within the quotes, with the
exception of `$', ``', `\', and, when history expansion is
enabled, `!'. The characters `$' and ``' retain their special
meaning within double quotes (*note Shell Expansions::).
and the manual here:
$ info '(bash)Command Substitution'
or here:
http://www.gnu.org/software/bash/manual/html_node/Shell-Expansions.html#Shell-Expansions
says:
3.5.4 Command Substitution
--------------------------
...
... When using the `$(COMMAND)' form, all characters between
the parentheses make up the command; none are treated
specially.
...
If the substitution appears within double quotes, word
splitting and filename expansion are not performed on the
results.
Could somebody please tell me what's going on here?
Sincerely,
Michael Witten
