Re: [gentoo-user] 'if echo hello' in .bashrc
Etaoin Shrdlu wrote: > On Saturday 9 May 2009, 12:15, Stroller wrote: > > On 8 May 2009, at 14:38, Stroller wrote: > > > ... > > > if echo hello|grep --color=auto l >/dev/null 2>&1; then > > >export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' > > > fi > > > > I'm afraid this thread has run away from me. I'm drinking the day's > > first cup of tea & rubbing my eyes furiously in confusion. Wha? > > I'm sure I'll comprehend the discussion better when I re-read later. > > However, is there actually any need to parse whether the grep supports > > colour before setting it? > > > > Let's say we use BSD grep or Schilling grep or whatever - is there > > actually any harm in exporting GREP_OPTIONS='--color=auto' in this > > case? > > Yes, because if the grep implementation in question supports GREP_OPTIONS > but doesn't support --color, you'll get errors when it's run. My "grep" is called "match" and it does not look at environment variables. There are few commands that have codumented (by POSIX) environment variables for options. I think of e.g. "make", that needs this in order to pass options to sub-makes. A safe method in shell scripts is to use lower case variable names. Jörg -- EMail:jo...@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin j...@cs.tu-berlin.de(uni) joerg.schill...@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/ URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily
Re: [gentoo-user] 'if echo hello' in .bashrc
On Sat, 9 May 2009 11:15:30 +0100 Stroller wrote: > Presumably BSD grep & all other greps also support the GREP_OPTIONS > environment variable? If it doesn't have support for the var then there should be no reason to pollute environment by setting it, possibly confusing the user which cares to look at it. -- Mike Kazantsev // fraggod.net signature.asc Description: PGP signature
Re: [gentoo-user] 'if echo hello' in .bashrc
On Saturday 9 May 2009, 12:43, Stroller wrote: > My question is: > Do BSD & other greps also support GREP_OPTIONS ? A quick google search reveals that NetBSD and FreeBSD use GNU grep, while OpenBSD uses BSD grep, which (at least according to the man page - see http://tinyurl.com/cs2unf) does not support GREP_OPTIONS. It seems that work is underway to port the BSD grep to FreeBSD and NeetBSD. See http://www.freebsd.org/cgi/man.cgi for a comprehensive list of manual pages for many popular unices. It seems that many greps do not support GREP_OPTIONS.
Re: [gentoo-user] 'if echo hello' in .bashrc
On 9 May 2009, at 11:41, Etaoin Shrdlu wrote: ... Let's say we use BSD grep or Schilling grep or whatever - is there actually any harm in exporting GREP_OPTIONS='--color=auto' in this case? Yes, because if the grep implementation in question supports GREP_OPTIONS but doesn't support --color, you'll get errors when it's run. (The assumption ... is that if --color is supported, then GREP_OPTIONS is too, which is reasonable and is what happens for GNU grep, although I cannot speak for other implementations). So this keeps the .bashrc compatible with older versions of GNU grep. That hadn't occurred to me. My question is: Do BSD & other greps also support GREP_OPTIONS ? Stroller.
Re: [gentoo-user] 'if echo hello' in .bashrc
On Saturday 9 May 2009, 12:15, Stroller wrote: > On 8 May 2009, at 14:38, Stroller wrote: > > ... > > if echo hello|grep --color=auto l >/dev/null 2>&1; then > >export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' > > fi > > I'm afraid this thread has run away from me. I'm drinking the day's > first cup of tea & rubbing my eyes furiously in confusion. Wha? > I'm sure I'll comprehend the discussion better when I re-read later. > However, is there actually any need to parse whether the grep supports > colour before setting it? > > Let's say we use BSD grep or Schilling grep or whatever - is there > actually any harm in exporting GREP_OPTIONS='--color=auto' in this > case? Yes, because if the grep implementation in question supports GREP_OPTIONS but doesn't support --color, you'll get errors when it's run. (The assumption the author made is that if --color is supported, then GREP_OPTIONS is too, which is reasonable and is what happens for GNU grep, although I cannot speak for other implementations).
Re: [gentoo-user] 'if echo hello' in .bashrc
On 8 May 2009, at 14:38, Stroller wrote: ... if echo hello|grep --color=auto l >/dev/null 2>&1; then export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' fi I'm afraid this thread has run away from me. I'm drinking the day's first cup of tea & rubbing my eyes furiously in confusion. Wha? I'm sure I'll comprehend the discussion better when I re-read later. However, is there actually any need to parse whether the grep supports colour before setting it? Let's say we use BSD grep or Schilling grep or whatever - is there actually any harm in exporting GREP_OPTIONS='--color=auto' in this case? Having written the above (so I might as well now send this message) it occurred to me to test it: $ GREP_OPTIONS='--not-suported' $ grep -i rabbit Alice\ in\ Wonderland.txt grep: unrecognized option '--not-suported' Usage: grep [OPTION]... PATTERN [FILE]... Try `grep --help' for more information. $ Presumably BSD grep & all other greps also support the GREP_OPTIONS environment variable? Stroller
Re: [gentoo-user] 'if echo hello' in .bashrc
* Carlos Hendson (skyc...@gmx.net) wrote: > [1] The reason an error message is shown here is because it's bash > that's reporting the broken pipe error. Grep's error message was > redirected to /dev/null, which was: > > grep: unrecognized option '--unsupported' > Usage: grep [OPTION]... PATTERN [FILE]... > Try `grep --help' for more information. > > So even when the system doesn't support --color, that original code will > pollute the screen with bash's error message. SIGPIPE behaviour depends on the shell, how it was built and its configuration so won't always receive an error. The point of this mail however is that there is still a way around it, just call the commands within a subshell. Compare: $ (echo hello | grep --colour l >/dev/null 2>&1) && echo colour support colour support $ (echo hello | grep --broken_arg l >/dev/null 2>&1) && echo broken_arg support with the original non-subshell'd version: $ echo hello | grep --broken_arg l >/dev/null 2>&1 && echo broken_arg support -bash: echo: write error: Broken pipe Thanks, James pgpekrCaEfOdK.pgp Description: PGP signature
Re: [gentoo-user] 'if echo hello' in .bashrc
On Fri, 8 May 2009 16:10:20 +0200 Alan McKinnon wrote: > On Friday 08 May 2009 16:01:14 Mike Kazantsev wrote: > > > Some greps (like BSD one) might not support '--color' option, so "echo > > hello|grep --color=auto l" will return error code, skipping if clause, > > and won't break grep operation by adding an unsupported option. > > except that STDERR is combined with STDOUT and sent to /dev/null so the > script > will never get it, the if is always true and the entire check is redundant. > Better would be > > if echo hello|grep --color=auto l >/dev/null ; then As many ppl just pointed out, you mistake "output check" done by "[" or "test" commands with shell built-in "if" statement operation, which looks only to a given command exit code, doesn't bothering with any output. "if [ $A ]" is equivalent to "if test $A" (where "test" is "/usr/bin/test"), except that modern shells implement test command as a built-in. For the rest of them, there's actually "/usr/bin/\[" symlink, which should exist on your system as well. So what happens is "test $A", silently returning it's exit code to "if". And of course, you can use any command instead of "test". For example there's also "/bin/true" and "/bin/false", so idiomatical "if true" and "if false" would actually work as expected ;) -- Mike Kazantsev // fraggod.net signature.asc Description: PGP signature
Re: [gentoo-user] 'if echo hello' in .bashrc
Alan McKinnon wrote: > On Friday 08 May 2009 16:01:14 Mike Kazantsev wrote: >> On Fri, 8 May 2009 14:38:58 +0100 >> >> Stroller wrote: >>> To find the part to which I refer you'll need to scroll down about >>> halfway through that page to "Colorize grep"; the author advises adding: >>> >>>if echo hello|grep --color=auto l >/dev/null 2>&1; then >>> export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' >>>fi >>> >>> to ~/.bashrc >>> >>> Why does he echo hello, please? >> Some greps (like BSD one) might not support '--color' option, so "echo >> hello|grep --color=auto l" will return error code, skipping if clause, >> and won't break grep operation by adding an unsupported option. > > except that STDERR is combined with STDOUT and sent to /dev/null so the > script > will never get it, the if is always true and the entire check is redundant. > Better would be > > if echo hello|grep --color=auto l >/dev/null ; then > The redirection of output doesn't affect the return code of grep in the above case. Grep's return code is determined by matching 'l' against the output of echo hello. The desired effect of the above code is to evaluate if the --color option is supported by grep on the system. The STDERR and STDOUT redirection is an attempt to not pollute the systems screen when performing that test. To illustrate: 1. A system that supports --color $ if echo hello|grep --color=auto l >/dev/null 2>&1; then echo "Grep returned : $?"; else echo "Grep returned : $?"; fi Grep returned : 0 2. A system that doesn't support --color (simulated by supplying --unspported as an option to grep) $ if echo hello|grep --unsupported l >/dev/null 2>&1; then echo "Grep returned : $?"; else echo "Grep returned : $?"; fi -bash: echo: write error: Broken pipe [1] Grep returned : 2 3. Just to complete the examples, the result of grep not matching echo's output but still supporting the --color option. (achieved by search "hello" for the letter 'z') $ if echo hello|grep --color z >/dev/null 2>&1; then echo "Grep returned : $?"; else echo "Grep returned : $?"; fi Grep returned : 1 Regards, Carlos [1] The reason an error message is shown here is because it's bash that's reporting the broken pipe error. Grep's error message was redirected to /dev/null, which was: grep: unrecognized option '--unsupported' Usage: grep [OPTION]... PATTERN [FILE]... Try `grep --help' for more information. So even when the system doesn't support --color, that original code will pollute the screen with bash's error message.
Re: [gentoo-user] 'if echo hello' in .bashrc
On Friday 8 May 2009, 16:51, Alan McKinnon wrote: > > > except that STDERR is combined with STDOUT and sent to /dev/null > > > so the script will never get it, the if is always true and the > > > entire check is redundant. Better would be > > > > > > if echo hello|grep --color=auto l >/dev/null ; then > > > > That will output an uncaptured error message if --color is not > > supported. > > which is the desired effect. It causes the if to be false and the grep > options are not enabled (as they are not supported) It's not the fact that the error message is left free to show on screen that makes the exit status true or false. If the file is sourced from a non-interactive environment, you don't want anything printed (and probably, in this case, neither if it's an interactive session). Capturing stderr does not change the exit status of the pipeline.
Re: [gentoo-user] 'if echo hello' in .bashrc
On 08.05.2009 17:10, Alan McKinnon wrote: >>>if echo hello|grep --color=auto l >/dev/null 2>&1; then >>> export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' >>>fi >>> >>> to ~/.bashrc >>> >>> Why does he echo hello, please? >> Some greps (like BSD one) might not support '--color' option, so "echo >> hello|grep --color=auto l" will return error code, skipping if clause, >> and won't break grep operation by adding an unsupported option. > > except that STDERR is combined with STDOUT and sent to /dev/null so the > script > will never get it, the if is always true and the entire check is redundant. > Better would be > > if echo hello|grep --color=auto l >/dev/null ; then No. We do not want any output from echo|grep. We just want the exit code so that the following export statement gets executed iff grep returns with no errors. -- Eray
Re: [gentoo-user] 'if echo hello' in .bashrc
On Friday 08 May 2009 16:59:19 Etaoin Shrdlu wrote: > On Friday 8 May 2009, 16:10, Alan McKinnon wrote: > > On Friday 08 May 2009 16:01:14 Mike Kazantsev wrote: > > > On Fri, 8 May 2009 14:38:58 +0100 > > > > > > Stroller wrote: > > > > To find the part to which I refer you'll need to scroll down about > > > > halfway through that page to "Colorize grep"; the author advises > > > > adding: > > > > > > > >if echo hello|grep --color=auto l >/dev/null 2>&1; then > > > > export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' > > > >fi > > > > > > > > to ~/.bashrc > > > > > > > > Why does he echo hello, please? > > > > > > Some greps (like BSD one) might not support '--color' option, so > > > "echo hello|grep --color=auto l" will return error code, skipping if > > > clause, and won't break grep operation by adding an unsupported > > > option. > > > > except that STDERR is combined with STDOUT and sent to /dev/null so > > the script will never get it, the if is always true and the entire > > check is redundant. Better would be > > > > if echo hello|grep --color=auto l >/dev/null ; then > > That will output an uncaptured error message if --color is not supported. which is the desired effect. It causes the if to be false and the grep options are not enabled (as they are not supported) -- alan dot mckinnon at gmail dot com
Re: [gentoo-user] 'if echo hello' in .bashrc
On Friday 8 May 2009, 16:10, Alan McKinnon wrote: > On Friday 08 May 2009 16:01:14 Mike Kazantsev wrote: > > On Fri, 8 May 2009 14:38:58 +0100 > > > > Stroller wrote: > > > To find the part to which I refer you'll need to scroll down about > > > halfway through that page to "Colorize grep"; the author advises > > > adding: > > > > > >if echo hello|grep --color=auto l >/dev/null 2>&1; then > > > export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' > > >fi > > > > > > to ~/.bashrc > > > > > > Why does he echo hello, please? > > > > Some greps (like BSD one) might not support '--color' option, so > > "echo hello|grep --color=auto l" will return error code, skipping if > > clause, and won't break grep operation by adding an unsupported > > option. > > except that STDERR is combined with STDOUT and sent to /dev/null so > the script will never get it, the if is always true and the entire > check is redundant. Better would be > > if echo hello|grep --color=auto l >/dev/null ; then That will output an uncaptured error message if --color is not supported.
Re: [gentoo-user] 'if echo hello' in .bashrc
On Friday 08 May 2009 16:38:30 Christian wrote: > Hi Alan, > > Am Freitag, 8. Mai 2009 schrieb Alan McKinnon: > > > Some greps (like BSD one) might not support '--color' option, so "echo > > > hello|grep --color=auto l" will return error code, skipping if clause, > > > and won't break grep operation by adding an unsupported option. > > is this really right? > > The result of > > if echo hello|grep --Acolor=auto l >/dev/null 2>&1; then echo hallo; fi > > is nothing. Which is equal to ), which in shell terms is true Yes, it's the opposite to other languages. Yes, it really should be that way. The return value of successful process is by convention 0, which therefore is evaluated as true. Non-zero is false > So the if clause is false although I pieped STDERR to > /dev/null. > > > except that STDERR is combined with STDOUT and sent to /dev/null so the > > script will never get it, the if is always true and the entire check is > > redundant. Better would be > > > > if echo hello|grep --color=auto l >/dev/null ; then > > grep writes to STDERR if an error is occured. > > The result of > > if echo hello|grep --Acolor=auto l >/dev/null ; then echo hallo; fi ^ What's this? I didn't type it. -- alan dot mckinnon at gmail dot com
Re: [gentoo-user] 'if echo hello' in .bashrc
Hi Alan, Am Freitag, 8. Mai 2009 schrieb Alan McKinnon: > > Some greps (like BSD one) might not support '--color' option, so "echo > > hello|grep --color=auto l" will return error code, skipping if clause, > > and won't break grep operation by adding an unsupported option. is this really right? The result of if echo hello|grep --Acolor=auto l >/dev/null 2>&1; then echo hallo; fi is nothing. So the if clause is false although I pieped STDERR to /dev/null. > except that STDERR is combined with STDOUT and sent to /dev/null so the > script will never get it, the if is always true and the entire check is > redundant. Better would be > > if echo hello|grep --color=auto l >/dev/null ; then grep writes to STDERR if an error is occured. The result of if echo hello|grep --Acolor=auto l >/dev/null ; then echo hallo; fi is: grep: Unbekannte Option »--Acolor=auto« Aufruf: grep [OPTION]... MUSTER [DATEI]... »grep --help« gibt Ihnen mehr Informationen. Best regard Christian
Re: [gentoo-user] 'if echo hello' in .bashrc
On Friday 08 May 2009 16:01:14 Mike Kazantsev wrote: > On Fri, 8 May 2009 14:38:58 +0100 > > Stroller wrote: > > To find the part to which I refer you'll need to scroll down about > > halfway through that page to "Colorize grep"; the author advises adding: > > > >if echo hello|grep --color=auto l >/dev/null 2>&1; then > > export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' > >fi > > > > to ~/.bashrc > > > > Why does he echo hello, please? > > Some greps (like BSD one) might not support '--color' option, so "echo > hello|grep --color=auto l" will return error code, skipping if clause, > and won't break grep operation by adding an unsupported option. except that STDERR is combined with STDOUT and sent to /dev/null so the script will never get it, the if is always true and the entire check is redundant. Better would be if echo hello|grep --color=auto l >/dev/null ; then -- alan dot mckinnon at gmail dot com
Re: [gentoo-user] 'if echo hello' in .bashrc
On 8 May 2009, at 15:01, Mike Kazantsev wrote: On Fri, 8 May 2009 14:38:58 +0100 Stroller wrote: To find the part to which I refer you'll need to scroll down about halfway through that page to "Colorize grep"; the author advises adding: if echo hello|grep --color=auto l >/dev/null 2>&1; then export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' fi to ~/.bashrc Why does he echo hello, please? Some greps (like BSD one) might not support '--color' option, so "echo hello|grep --color=auto l" will return error code, skipping if clause, and won't break grep operation by adding an unsupported option. Ah! I see! Many thanks! Stroller.
Re: [gentoo-user] 'if echo hello' in .bashrc
On Fri, 8 May 2009 14:38:58 +0100 Stroller wrote: > To find the part to which I refer you'll need to scroll down about > halfway through that page to "Colorize grep"; the author advises adding: > >if echo hello|grep --color=auto l >/dev/null 2>&1; then > export GREP_OPTIONS='--color=auto' GREP_COLOR='1;32' >fi > > to ~/.bashrc > > Why does he echo hello, please? Some greps (like BSD one) might not support '--color' option, so "echo hello|grep --color=auto l" will return error code, skipping if clause, and won't break grep operation by adding an unsupported option. -- Mike Kazantsev // fraggod.net signature.asc Description: PGP signature
