Question

I am not getting results back from grep when I call it with a param containing curly braces using Ruby’s “ or %x{} expressions.

Say I have these files in an empty directory:

$ echo '**hello**' > hello.md
$ echo 'hello' > hello.txt

If I only want results matching a single extension, Ruby works as expected:

$ grep -rn hello . --include=*.txt
./hello.txt:1:hello

$ grep -rn hello . --include=*.md
./hello.md:1:**hello**

$ irb

ree-1.8.7-2011.03 :001 > `grep -rn hello . --include=*.txt`
=> "./hello.txt:1:hello\n"

ree-1.8.7-2011.03 :002 > %x{grep -rn hello . --include=*.md}
=> "./hello.md:1:**hello**\n" 

ree-1.8.7-2011.03 :003 > exit

But if I ask for results matching either extension, using grep’s curly brace syntax, no results come up with Ruby:

$ grep -rn hello . --include=*.{txt,md}
./hello.txt:1:hello
./hello.md:1:**hello**

$ irb

ree-1.8.7-2011.03 :001 > `grep -rn hello . --include=*.{txt,md}`
=> ""

ree-1.8.7-2011.03 :002 > %x{grep -rn hello . --include=*.{txt,md}}
=> ""

Edit: echoing works, but command results are still empty:

ruby-1.9.2-p180 :004 > `echo grep -rn hello . --include=*.{txt,md}`
=> "grep -rn hello . --include=*.{txt,md}\n" 

ruby-1.9.2-p180 :005 > `grep -rn hello . --include=*.{txt,md}`
=> "" 

How can I debug this and see the actual command being executed? And what’s the correct way to execute system commands with curly braces in the params from Ruby?

Answer 1

Here’s a guess: %x{} is using /bin/sh which isn’t behaving like /bin/bash (or your usual shell).

This pattern:

*.{txt,md}

is expanded by your shell just like all the other file globbing patterns. When you run your command from within irb, Ruby is probably using /bin/sh to execute the command and on your system, /bin/sh behaves like a plain POSIX shell which doesn’t understand the *.{a,b} globbing syntax.

Try invoking bash directly:

irb> `bash -c 'grep -rn hello . --include=*.{txt,md}'`