Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: darwin17.5.0
Compiler: clang
Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64'
-DCONF_OSTYPE='darwin17.5.0' -DCONF_MACHTYPE='x86_64-apple-darwin17.5.0'
-DCONF_VENDOR='apple' -DLOCALEDIR='/usr/local/Cellar/bash/4.4.23/share/locale'
-DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H -DMACOSX -I. -I. -I./include
-I./lib -I./lib/intl -I/private/tmp/bash-20180602-817-1lkxzgr/bash-4.4/lib/intl
-DSSH_SOURCE_BASHRC -Wno-parentheses -Wno-format-security
uname output: Darwin pop-jpas-mbpr-4.local 17.7.0 Darwin Kernel Version 17.7.0:
Fri Nov 2 20:43:16 PDT 2018; root:xnu-4570.71.17~1/RELEASE_X86_64 x86_64
Machine Type: x86_64-apple-darwin17.5.0
Bash Version: 4.4
Patch Level: 23
Release Status: release
Description:
The `read` builtin skips null characters and does not count
them toward the limit specified by -n/-N. This leads to
surprising behavior with /dev/zero: read -N 1 </dev/zero
never terminates!
This is obviously a corner case but it violates what ought
to be a safe user assumption that specifying -N prevents
read from running for too long.
Repeat-By:
$ tr \\0 a </dev/zero | read -N # terminates immediately
$ tr \\0 \\0 </dev/zero | read -N # runs forever
or in the absence of /dev/zero:
$ while true ; do echo -n a ; done | read -N 1 # terminates
$ while true ; do echo -n a ; done | tr a \\0 | read -N 1 # runs forever
Fix:
I propose to count nulls toward nchars.
In the patch I replaced a `continue` with a `goto` that should
result in equivalent behavior except for the case I'm raising
here. The only other place that the input char doesn't count
toward nchars is when it's a backslash or a newline just after a
backslash, and -r is not specified. I see no need to disrupt
that behavior, but the case could be made; I leave it to the
maintainers.
diff --git a/builtins/read.def b/builtins/read.def
index b57c8c398e18..5713766e4c3a 100644
--- a/builtins/read.def
+++ b/builtins/read.def
@@ -672,7 +672,7 @@ read_builtin (list)
break;
if (c == '\0' && delim != '\0')
- continue; /* skip NUL bytes in input */
+ goto increment_byte_count; /* skip NUL bytes in input */
if ((skip_ctlesc == 0 && c == CTLESC) || (skip_ctlnul == 0 && c ==
CTLNUL))
{
@@ -713,6 +713,7 @@ add_char:
}
#endif
+increment_byte_count:
nr++;
if (nchars > 0 && nr >= nchars)
diff --git a/tests/read.right b/tests/read.right
index 73cb7042fbca..649c78a568c5 100644
--- a/tests/read.right
+++ b/tests/read.right
@@ -45,6 +45,7 @@ abcde
abc
ab
abc
+ac
#
while read -u 3 var
do
diff --git a/tests/read3.sub b/tests/read3.sub
index af41e3f27930..02334fdad6d2 100644
--- a/tests/read3.sub
+++ b/tests/read3.sub
@@ -20,5 +20,11 @@ echo abc | {
echo $foo
}
+# does not consume too many characters
+echo abcde | tr b '\0' | {
+ read -N 3 foo
+ echo $foo
+}
+
read -n 1 < $0
echo "$REPLY"
