06-26-2012
The behavior you describe is normal. What you probably want is to switch stdout from fully buffered to line buffered (assuming your writes are each terminated by a newline).
Quote:
When a stream is "unbuffered", bytes are intended to appear from the source or at the destination as soon as possible; otherwise, bytes may be accumulated and transmitted as a block. When a stream is "fully buffered", bytes are intended to be transmitted as a block when a buffer is filled. When a stream is "line buffered", bytes are intended to be transmitted as a block when a <newline> byte is encountered. Furthermore, bytes are intended to be transmitted as a block when a buffer is filled, when input is requested on an unbuffered stream, or when input is requested on a line-buffered stream that requires the transmission of bytes. Support for these characteristics is implementation-defined, and may be affected via setbuf() and setvbuf().
...<snip>...
At program start-up, three streams are predefined and need not be opened explicitly: standard input (for reading conventional input), standard output (for writing conventional output), and standard error (for writing diagnostic output). When opened, the standard error stream is not fully buffered; the standard input and standard output streams are fully buffered if and only if the stream can be determined not to refer to an interactive device.
2.5 Standard I/O Streams
Regards,
Alister
This User Gave Thanks to alister For This Post:
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LEARN ABOUT DEBIAN
cmdtest
CMDTEST(1) General Commands Manual CMDTEST(1)
NAME
cmdtest - blackbox testing of Unix command line tools
SYNOPSIS
cmdtest [-c=COMMAND] [--command=COMMAND] [--config=FILE] [--dump-config] [--dump-memory-profile=METHOD] [--dump-setting-names]
[--generate-manpage=TEMPLATE] [-h] [--help] [-k] [--keep] [--list-config-files] [--log=FILE] [--log-keep=N] [--log-level=LEVEL]
[--log-max=SIZE] [--no-default-configs] [--output=FILE] [-t=TEST] [--test=TEST] [--timings] [--version] [FILE]...
DESCRIPTION
cmdtest black box tests Unix command line tools. Given some test scripts, their inputs, and expected outputs, it verifies that the command
line produces the expected output. If not, it reports problems, and shows the differences.
Each test case foo consists of the following files:
foo.script
a script to run the test (this is required)
foo.stdin
the file fed to standard input
foo.stdout
the expected output to the standard output
foo.stderr
the expected output to the standard error
foo.exit
the expected exit code
foo.setup
a shell script to run before the test
foo.teardown
a shell script to run after test
Usually, a single test is not enough. All tests are put into the same directory, and they may share some setup and teardown code:
setup-once
a shell script to run once, before any tests
setup a shell script to run before each test
teardown
a shell script to run after each test
teardown-once
a shell script to run once, after all tests
cmdtest is given the name of the directory with all the tests, or several such directories, and it does the following:
o execute setup-once
o for each test case (unique prefix foo):
-- execute setup
-- execute foo.setup
-- execute the command, by running foo.script, and redirecting standard input to come from foo.stdin, and capturing standard output
and error and exit codes
-- execute foo.teardown
-- execute teardown
-- report result of test: does exit code match foo.exit, standard output match foo.stdout, and standard error match foo.stderr?
o execute teardown-once
Except for foo.script, all of these files are optional. If a setup or teardown script is missing, it is simply not executed. If one of
the standard input, output, or error files is missing, it is treated as if it were empty. If the exit code file is missing, it is treated
as if it specified an exit code of zero.
The shell scripts may use the following environment variables:
DATADIR
a temporary directory where files may be created by the test
TESTNAME
name of the current test (will be empty for setup-once and teardown-once)
SRCDIR directory from which cmdtest was launched
OPTIONS
-c, --command=COMMAND
ignored for backwards compatibility
--config=FILE
add FILE to config files
--dump-config
write out the entire current configuration
--dump-memory-profile=METHOD
make memory profiling dumps using METHOD, which is one of: none, simple, meliae, or heapy (default: simple)
--dump-setting-names
write out all names of settings and quit
--generate-manpage=TEMPLATE
fill in manual page TEMPLATE
-h, --help
show this help message and exit
-k, --keep
keep temporary data on failure
--list-config-files
list all possible config files
--log=FILE
write log entries to FILE (default is to not write log files at all); use "syslog" to log to system log
--log-keep=N
keep last N logs (10)
--log-level=LEVEL
log at LEVEL, one of debug, info, warning, error, critical, fatal (default: debug)
--log-max=SIZE
rotate logs larger than SIZE, zero for never (default: 0)
--no-default-configs
clear list of configuration files to read
--output=FILE
write output to FILE, instead of standard output
-t, --test=TEST
run only TEST (can be given many times)
--timings
report how long each test takes
--version
show program's version number and exit
EXAMPLE
To test that the echo(1) command outputs the expected string, create a file called echo-tests/hello.script containing the following con-
tent:
#!/bin/sh
echo hello, world
Also create the file echo-tests/hello.stdout containing:
hello, world
Then you can run the tests:
$ cmdtest echo-tests
test 1/1
1/1 tests OK, 0 failures
If you change the stdout file to be something else, cmdtest will report the differences:
$ cmdtest echo-tests
FAIL: hello: stdout diff:
--- echo-tests/hello.stdout 2011-09-11 19:14:47 +0100
+++ echo-tests/hello.stdout-actual 2011-09-11 19:14:49 +0100
@@ -1 +1 @@
-something else
+hello, world
test 1/1
0/1 tests OK, 1 failures
Furthermore, the echo-tests directory will contain the actual output files, and diffs from the expected files. If one of the actual output
files is actually correct, you can actualy rename it to be the expected file. Actually, that's a very convenient way of creating the ex-
pected output files: you run the test, fixing things, until you've manually checked the actual output is correct, then you rename the file.
SEE ALSO
cliapp(5).
CMDTEST(1)