When I run:
$ man echo
Does not display any information regarding the flag "-e" on OSX 10.10.3, however clearly that flag exists:
$ echo "\xFF" > hex
$ cat hex
\xFF
$ echo -e "\xFF" > hex
$ cat hex
?
Can anyone explain this ? Can the man pages ever be incomplete?
Related
When running the following command with xargs (GNU findutils) 4.7.0
xargs -n1 <<<"-d -e -n -o"
I get this output
-d
-o
Why is -e and -n not present in the output?
From man xargs:
[...] and executes the command (default is /bin/echo) [...]
So it runs:
echo -d
echo -e
echo -n
echo -o
But from man echo:
-n do not output the trailing newline
-e enable interpretation of backslash escapes
And echo -n outputs nothing, and echo -e outputs one empty newlines that you see in the output.
With Sed, I want to use "!" to exclude lines that matches "he". Here is an example.
echo "hello" |sed "/he/!s/hello/hi/"
To my surprise, my ubuntu 14 returns
"bash !s/hello/hi: event not found"
error. Any ideas? How could I exclude line ranges corresponding to a pattern with Sed?
You have history expansion enabled. You need to disable it with set +H.
Example
Let's enable history expansion and run your command:
$ set -H
$ echo "hello" |sed "/he/!s/hello/hi/"
bash: !s/hello/hi/: event not found
Now, let's disable it and observe that the command now runs correctly and without error:
$ set +H
$ echo "hello" |sed "/he/!s/hello/hi/"
hello
Alternative
If you want to keep history expansion enabled, then single-quote your string:
$ set -H
$ echo "hello" |sed '/he/!s/hello/hi/'
hello
"ls" behaves differently when its output is being piped:
> ls ???
bar foo
> ls ??? | cat
bar
foo
How does it know, and how would I do this in Perl?
In Perl, the -t file test operator indicates whether a filehandle
(including STDIN) is connected to a terminal.
There is also the -p test operator to indicate whether a filehandle
is attached to a pipe.
$ perl -e 'printf "term:%d, pipe:%d\n", -t STDIN, -p STDIN'
term:1, pipe:0
$ perl -e 'printf "term:%d, pipe:%d\n", -t STDIN, -p STDIN' < /tmp/foo
term:0, pipe:0
$ echo foo | perl -e 'printf "term:%d, pipe:%d\n", -t STDIN, -p STDIN'
term:0, pipe:1
File test operator documentation at perldoc -f -X.
use IO::Interactive qw(is_interactive);
is_interactive() or warn "Being piped\n";
The terminal transcript speaks for itself:
iMac:~$ echo -n a | md5
0cc175b9c0f1b6a831c399e269772661
iMac:~$ perl -e 'system "echo -n a | md5"'
c3392e9373ccca33629d82b17699420f
Note that the MD5 hash of a is 0cc175b9c0f1b6a831c399e269772661, the first
result. Why does it turns out to be different when the same command is called
by perl?
By the way, perl is perl 5, version 12, subversion 4 (v5.12.4) built for darwin-thread-multi-2level. And the system: Mac OS 10.8, Darwin 12.0
When in the /bin/sh shell on mac, echo -n doesn't not print out the newline like it does in /bin/bash. You can see this if you drop into /bin/sh and run echo -n a, your output should look like this:
sh-3.2$ echo -n a
-n a
so you're literally getting -n a instead of the desired a. As perl system runs /bin/sh to evaluate your command, -n a is being passed into md5 instead of your desired a
The specific question has already been answered, but I want to point out that od is useful to help understand exactly what any command outputs or file contains. This is useful especially to show otherwise non-printing characters.
$ echo -n a | od -tc
0000000 a
0000001
$ perl -e 'system "echo -n a | od -tc";'
0000000 - n a \n
0000005
i want to trim an output of wipe command with sed.
i try to use this one:
wipe -vx7 /dev/sdb 2>&1 | sed -u 's/.*\ \([0-9]\+\).*/\1/g'
but it don't work for some reason.
when i use echo & sed to print the output of wipe command it works!
echo "/dev/sdb: 10%" | sed -u 's/.*\ \([0-9]\+\).*/\1/g'
what i'm doing wrong?
Thanks!
That looks like a progress indicator. They are often output directly to the tty instead of to stdout or stderr. You may be able to use the expect script called unbuffer (source) or some other method to create a pseudo tty. Be aware that there will probably be more junk such as \r, etc., that you may need to filter out.
Demonstration:
$ cat foo
#!/bin/sh
echo hello > /dev/tty
$ a=$(./foo)
hello
$ echo $a
$ a=$(unbuffer ./foo)
$ echo $a
hello