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I have a script that does some housekeeping that works perfectly well when invoked from an interactive shell, but did nothing when invoked by cron. To troubleshoot this I started a shell with a 'blank' environment with the command:

env -i /bin/bash --noprofile --norc

Using this blank env I've dug into my script and found that the following grep will not match any files:

grep -il "^ws_status\s*=\s*[\"']remove[\"']$"

However, when run from an interactive shell the command will return the filenames of the matching files.

As a note, the expression is matching lines like: WS_STATUS = "remove"

Through trial-and-error I discovered that adding -P to the options [Perl regex] the command started working normally in the 'blank' shell. However, I have no idea why my login shell appears to be defaulted to grep -P.

  • There is only one grep binary, /bin/grep
  • There are no aliases defined for grep=pgrep or grep="grep -P"
  • There is no env variable GREP_OPTIONS defined.

What's the deal here?

Note: OS is RHEL v5.10, Bash is v3.2.25, grep is v2.5.1

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so in your interactive shell, which grep returns grep -P? Did you do a recursive grep for "grep -P" in /etc/profile*? –  Petter H Oct 24 '13 at 18:23
@PetterH which grep returns /bin/grep, and grep -ri grep /etc/profile* only prints out a few uses of it in the scripts. –  Sammitch Oct 24 '13 at 18:49
Rather than which grep can you try type grep. –  Mark Wagner Oct 24 '13 at 19:29
@MarkWagner grep is hashed (/bin/grep) –  Sammitch Oct 24 '13 at 20:18
which is useless. What does type -a grep output? (note the -a option) Part of the reason for the difference in behavior is that an interactive shell often has a different PATH than the environment of cron. –  Dennis Williamson Oct 24 '13 at 21:12
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