Re: make

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Author: Phil Waclawski
Date:  
To: Main PLUG discussion list
Subject: Re: make
I really don't know. I've had a lot of students who seem to think that you
HAVE to cat to grep, and I can assure you, I do my best to correct them.

Phil W


On Mon, Aug 25, 2014 at 4:51 PM, Michael Havens <> wrote:

> I get it!
>
>    cat x | grep y

>
> is redundant. did I learn that when it wasn't redundant? if it never has
> been redundant I wonder why I thought the pipe was needed?
>
> :-)~MIKE~(-:
>
>
> On Mon, Aug 25, 2014 at 4:25 PM, Brian Cluff <> wrote:
>
>> You'll need to add some single quotes to keep the shell from interpreting
>> your regex as shell code like this:
>>
>> grep -E 'error|fail' {make,install,check}.fail
>>
>> Without the single quotes you are telling the system to cat from your set
>> of files and look for lines with the word error and pipe that to a program
>> called fail.
>>
>> I found that I did have to add the -E even thought the man page says that
>> in the GNU version of grep the basic and extended regular expressions are
>> the same... it appears that is not the case in practice.
>>
>> Brian Cluff
>>
>>
>> On 08/25/2014 12:56 PM, Michael Havens wrote:
>>
>>> I have 3 files, make.fail, install.fail, and check.fail. I want to check
>>> for two words in those files: error and fail.
>>>
>>> would this work?
>>>
>>> cat {make,install,check}.fail | grep -i error|fail
>>>
>>> I was told to put the 'E' option in to grep. Looking at the man page it
>>> seems that the E option is only useful if I were greping for something
>>> that begins with a '{'. AM I misreading the man page?
>>>
>>> man quote:
>>>         GNU grep -E attempts to support traditional usage by assuming
>>> that { is
>>>         not   special  if  it  would  be  the  start  of  an  invalid
>>> interval
>>>         specification.  For example, the command grep -E '{1' searches
>>> for  the
>>>         two-character  string  {1  instead  of  reporting a syntax error
>>> in the
>>>         regular expression.  POSIX allows this behavior as  an
>>> extension,  but
>>>         portable scripts should avoid it.

>>>
>>>
>>>
>>> :-)~MIKE~(-:
>>>
>>>
>>> On Mon, Aug 25, 2014 at 12:24 PM, Michael Havens <
>>> <mailto:bmike1@gmail.com>> wrote:
>>>
>>>     you guys are so helpful! Thanks.

>>>
>>>     :-)~MIKE~(-:

>>>
>>>
>>>     On Sun, Aug 24, 2014 at 7:40 PM, Jon Kettenhofen <
>>>     <mailto:subs@kexsof.com>> wrote:

>>>
>>>         I like visible proofs, so here's a test I ran:
>>>         (terminal output was as is shown)

>>>
>>>         [jon@localhost ~]$ rm temp
>>>         [jon@localhost ~]$ echo >>temp
>>>         [jon@localhost ~]$ echo $?
>>>         0
>>>         [jon@localhost ~]$ cat temp

>>>
>>>         [jon@localhost ~]$ echo >>temp 2>&1
>>>         [jon@localhost ~]$ echo $?
>>>         0
>>>         [jon@localhost ~]$ cat temp

>>>
>>>
>>>         [jon@localhost ~]$

>>>
>>>         as you can see, no errors and the single ">" did not erase the
>>>         file when used in this manner.  So Mike's script should work as
>>>         intended
>>>         at least if there is no stderr output.

>>>
>>>         but suppose there was an error? (apologizing for the length of
>>> ...)

>>>
>>>         [jon@localhost ~]$ echo "echo" >test
>>>         [jon@localhost ~]$ echo "ls temp2" >>test
>>>         [jon@localhost ~]$ # test ls of non-existent file
>>>         [jon@localhost ~]$ ls temp2
>>>         ls: cannot access temp2: No such file or directory
>>>         [jon@localhost ~]$ echo $?
>>>         2
>>>         [jon@localhost ~]$ # see, we get both an error and stderr
>>> message
>>>         [jon@localhost ~]$ # so
>>>         [jon@localhost ~]$ mv test test.sh
>>>         [jon@localhost ~]$ chgmod +x test.sh
>>>         bash: chgmod: command not found...
>>>         [jon@localhost ~]$ chmod +x test.sh
>>>         [jon@localhost ~]$ # i'm not perfect!
>>>         [jon@localhost ~]$ rm temp
>>>         [jon@localhost ~]$ ./test.sh >>temp
>>>         ls: cannot access temp2: No such file or directory
>>>         [jon@localhost ~]$ echo $?
>>>         2
>>>         [jon@localhost ~]$ cat temp

>>>
>>>         [jon@localhost ~]$ ./test.sh >>temp 2>&1
>>>         [jon@localhost ~]$ echo $?
>>>         2
>>>         [jon@localhost ~]$ cat temp

>>>
>>>
>>>         ls: cannot access temp2: No such file or directory
>>>         [jon@localhost ~]$

>>>
>>>         as you can see, Mike's script will work as he apparently
>>> intended,
>>>         providing he's using a modern version of bash.

>>>
>>>
>>>
>>>         On 08/24/2014 09:56 PM, James Mcphee wrote:

>>>
>>>             you've said make, append stdout (default file descriptor 1)
>>>             to file
>>>             make.fail, assign stderr (default filedescriptor 2) the same
>>>             filedescriptor as stdout.  So...  If the intent was to have
>>>             both stderr
>>>             and stdout append make.fail, then it is correct.

>>>
>>>
>>>             On Sun, Aug 24, 2014 at 6:06 PM, Michael Havens
>>>             < <mailto:bmike1@gmail.com>
>>>             <mailto:bmike1@gmail.com <mailto:bmike1@gmail.com>>> wrote:

>>>
>>>                  what I really need to know is will this:

>>>
>>>                      make>>make.fail 2>&1

>>>
>>>                  send stderr and stdout to the file 'make.fail' or did I
>>>             write it
>>>                  incorrectly?

>>>
>>>                  :-)~MIKE~(-:

>>>
>>>
>>>                  On Sun, Aug 24, 2014 at 2:56 PM, Brian Cluff
>>>             < <mailto:brian@snaptek.com>
>>>                  <mailto:brian@snaptek.com <mailto:brian@snaptek.com>>>

>>>
>>>             wrote:

>>>
>>>                      the > will delete any file that it points at even
>>>             if the command
>>>                      doesn't actually output anything.  It will even
>>>             delete the file
>>>                      is the command doesn't exist like if you type grep
>>>             as gerp
>>>                       >file, file will still be created/overwritten.

>>>
>>>                      If you want to make sure that your command doesn't
>>>             overwrite any
>>>                      existing files you have to set the noclobber option
>>>             like:
>>>                      $ set -o noclobber

>>>
>>>                      A good trick to know:
>>>                      You can use the > to delete the contents of a file
>>>             without
>>>                      having to delete and recreate the file by simply
>>>             doing this:
>>>                      $ >yourfile

>>>
>>>                      Brian Cluff

>>>
>>>
>>>                      On 08/24/2014 02:36 PM, Michael Havens wrote:

>>>
>>>                          I have a question about redirections:

>>>
>>>                               make>>make.fail 2>&1

>>>
>>>                          tells it make and then to send (>) stderr (2)
>>>             to stdout (1)
>>>                          and also to
>>>                          send stdout that way also (&1). finally all of
>>>             that gets
>>>                          sent to a file
>>>                          named make.fail (>>). Isn't '>>' actually
>>>             'append' whereas
>>>                          '>' would
>>>                          work just as well so long as the file didn't
>>>             already exist?
>>>                          If the file
>>>                          did exist would I get an error or would the
>>>             file be overwritten?
>>>                          :-)~MIKE~(-:

>>>
>>>
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>>>
>>>             --
>>>             James McPhee
>>>              <mailto:jmcphe@gmail.com>
>>>             <mailto:jmcphe@gmail.com <mailto:jmcphe@gmail.com>>

>>>
>>>
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