Re: Passing multiple search directories to grep

[Andreas Kusalananda Kähäri]

On Tue, Aug 03, 2021 at 08:55:23AM -0400, Greg Wooledge wrote:
> On Tue, Aug 03, 2021 at 12:10:21PM +0000, hancooper wrote:
> > On Tuesday, August 3, 2021 11:32 AM, Greg Wooledge <greg@wooledge.org> 
> > wrote:
> > > So, if this command works on your system:
> > >
> > > grep -rl PATH /tmp /var/tmp
> > >
> > > then the same command generated using an array expansion will also work.
> 
> > Do you understand how grep distinguishes the search pattern from the search 
> > directories ?
> 
> Yes.  The search pattern is the first argument string (after options
> have been processed and removed).  All of the argument strings after
> the pattern are files or directories to be read.  If there are no
> arguments after the pattern, then standard input is read.
> 
> This is made clear by the man page:
> 
> SYNOPSIS
>        grep [-E|-F] [-c|-l|-q] [-insvx] -e pattern_list
>            [-e pattern_list]... [-f pattern_file]... [file...]
> 
>        grep [-E|-F] [-c|-l|-q] [-insvx] [-e pattern_list]...
>            -f pattern_file [-f pattern_file]... [file...]
> 
>        grep [-E|-F] [-c|-l|-q] [-insvx] pattern_list [file...]
> 
> In the absence of -e and -f, you're using the last form, where the
> pattern_list is a single argument, followed by zero or more files.
> 
> (The processing of directories with a -r option is a GNU extension.)
> 
> > I would prefer that my script does not impose any restriction on the search 
> > patterns allowed
> > by grep, because currently "$ptrn" is just a user-defined string.
> 
> In that case, use the -- indicator before the pattern.
> 
> grep -rl -- "$ptrn" "${dirlist[@]}"
> 
> This will ensure that grep doesn't treat the pattern as an option, even
> if it happens to begin with a hyphen.

Alternatively, and IMHO better in a "showing intention" sort of way,

        grep -r -l -e "$ptrn" -- "${dirlist[@]}"

I.e., use "-e" to designate the pattern, and then "--" to delimit the
file operands from the options.  But depending on what the pathnames
that are outputted from this are used for, I might suggest using "find"
in combination with "grep -q" instead, without either of "-r" or "-l".


-- 
Andreas (Kusalananda) Kähäri
SciLifeLab, NBIS, ICM
Uppsala University, Sweden

.