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Execution problem with grep script (2 variables)

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# 8  
Old 06-02-2010
You don't need to use eval - or egrep if you escape the infix |

Of course it runs... maybe it just doesn't find anything?

Show some of your input file

Code:
$ echo cats and dogs > file1
$ GREP=$(which grep)
$ $GREP "cats\|dogs" file1
cats and dogs

This User Gave Thanks to Scott For This Post:
jazzaddict
# 9  
Old 06-03-2010
Quote:
Originally Posted by pseudocoder
What does that mean in concrete terms? Is there no output?

Did you try to run that command in the shell and see if it will work?
Code:
/usr/bin/grep -i 'dog\|cat' test.log

Also try
Code:
/usr/bin/grep -iE 'dog\|cat' test.log

Code:
 grep -i 'dog\|cat' test.log

works in the shell! but /usr/bin/grep -i 'dog\|cat' test.log doesn't

---------- Post updated at 11:03 PM ---------- Previous update was at 10:59 PM ----------

Test file for grep input
Code:
this is a cat.
this is a dog.
this is a fox.
this is a bird.
this is a frog.
And cat and dogs are Man's best friends.

I made the following changes and the script now runs fine:

Code:
#!/bin/sh
TEST=animal.log

eval "grep -i 'dog\|cat' ${TEST}"

output:
Code:
this is a cat.
this is a dog.
And cat and dogs are Man's best friends.

i then do a whereis grep:

Code:
grep: /usr/bin/grep /usr/local/bin/grep /usr/man/man1/grep.1

I really don't understand why
Code:
#!/bin/sh
TEST=test.log
GREP=/usr/bin/grep

eval "$GREP -i 'dog\|cat' ${TEST}"

doesn't work
# 10  
Old 06-03-2010
Standard grep uses POSIX BRE's (Basic regular expressions) which do not include alternation. So one should use egrep for that which supports ERE's (Extended Regular Expressions). The reason that \| works with grep for some is that GNU grep added this as an extension to BRE, but this is not standard.
This User Gave Thanks to Scrutinizer For This Post:
jazzaddict
# 11  
Old 06-03-2010
Quote:
Originally Posted by Scrutinizer
Standard grep uses POSIX BRE's (Basic regular expressions) which do not include alternation. So one should use egrep for that which supports ERE's (Extended Regular Expressions). The reason that \| works with grep for some is that GNU grep added this as an extension to BRE, but this is not standard.
thanks you for the detailed explanation about "\|", after using egrep instead, everything works out fine Smilie
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