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Negating shell interpretation

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# 8  
Old 01-22-2012
Try:
Code:
#!/bin/ksh

final="test bla bla"
line="01 01 * * 5 /home/user01/bin/start"

if echo "$line" | grep 'start' >/dev/null 2>&1
then
  start="$final"
fi

echo "$start"

Or without external programs...

Code:
#!/bin/ksh

final="test bla bla"
line="01 01 * * 5 /home/user01/bin/start"

case $line in
  *start*) start="$final"
esac

echo "$start"

Last edited by Scrutinizer; 01-22-2012 at 01:28 PM..
# 9  
Old 01-22-2012
Why use grep at all? Take advantage of Kshell's pattern matching:

Code:
#!/usr/bin/env ksh

final="test bla bla"
line="01 01 * * 5 /home/user01/bin/start"

if [[ $line == *"start"* ]]
then
  start="$final"
fi

Depending on how this is being used, and thus the number of grep processes that are avoided, this is much more efficient.
This User Gave Thanks to agama For This Post:
ahamed101
# 10  
Old 01-22-2012
Quote:
Originally Posted by agama
Why use grep at all? Take advantage of Kshell's pattern matching:

Code:
#!/usr/bin/env ksh

final="test bla bla"
line="01 01 * * 5 /home/user01/bin/start"

if [[ $line == *"start"* ]]
then
  start="$final"
fi

Depending on how this is being used, and thus the number of grep processes that are avoided, this is much more efficient.

Why limit it to ksh? Scrutinizer's case statement (which also avoids external commands) will work in all Bourne-type shells.
This User Gave Thanks to cfajohnson For This Post:
agama
# 11  
Old 01-22-2012
Quote:
Originally Posted by cfajohnson

Why limit it to ksh? Scrutinizer's case statement (which also avoids external commands) will work in all Bourne-type shells.
Right. I missed the case example and specifically mentioned kshell because the original post indicated kshell was being used.
# 12  
Old 01-22-2012
Hey guys,

Thanks for all the input so far. It's been really helpful. It looks like this line is working currently:
Code:
if [[ $line == *"start"* ]]


In this following snippet, line 9 only needs one set of square brackets but lines 13 and 16 needs two set of square brackets. Any thoughts?
Code:
     8	function match {
     9	    temp=$( echo "$line" | egrep '(start|stop)' )
    10	    
    11	    if [ ! -z "$temp" ]
    12	    then
    13		if [[ $( echo "$temp" | grep 'start') ]]
    14		then
    15		    start="$temp"
    16		elif  [[ $( echo "$temp" | grep 'stop') ]]
    17		then
    18		    end="$temp"
    19		fi
    20	    fi
    21	}

# 13  
Old 01-22-2012
The open square bracket [ is a symbolic link to the test command and gives the appearance of wrapping the expression in parenthesis-like format that most programmers are used to. The double bracket, is a part of the shell syntax.

The expression that appears between single brackets is given to the test command while the expression inside of double brackets is interpreted by the shell. The shell interpretation supports the evaluation of the command exit code like you want to do, while the test command does not and that is why you need the double brackets where you've discovered that you do.

In my humble opinion, there is rarely a case where single brackets (the test command) are needed; using double bracketed expressions is much more efficient especially when loops are involved.
Last edited by agama; 01-22-2012 at 07:06 PM.. Reason: typo
# 14  
Old 01-22-2012
Quote:
Originally Posted by sprucio
Hey guys,

Thanks for all the input so far. It's been really helpful. It looks like this line is working currently:
Code:
if [[ $line == *"start"* ]]


In this following snippet, line 9 only needs one set of square brackets but lines 13 and 16 needs two set of square brackets. Any thoughts?
Code:
     8	function match {
     9	    temp=$( echo "$line" | egrep '(start|stop)' )
    10	    
    11	    if [ ! -z "$temp" ]
    12	    then
    13		if [[ $( echo "$temp" | grep 'start') ]]
    14		then
    15		    start="$temp"
    16		elif  [[ $( echo "$temp" | grep 'stop') ]]
    17		then
    18		    end="$temp"
    19		fi
    20	    fi
    21	}


You don't need grep, and you don't need double (or single) brackets.

Use case:
Code:
match() {
  case $line in
    *start*) start=$line ;;
    *stop*)  end=$line ;;
  esac
}

---------- Post updated at 06:12 PM ---------- Previous update was at 06:06 PM ----------

Quote:
Originally Posted by agama
The open square bracket [ is a symbolic link to the test command and gives the appearance of wrapping the expression in parenthesis-like format that most programmers are used to.

The open square bracket [ is a shell builtin command, and it is synonymous with test:
Code:
$ type test [   
test is a shell builtin
[ is a shell builtin

Quote:
In my humble opinion, there is rarely a case where single brackets (the test command) are needed; using double bracketed expressions is much more efficient especially when loops are involved.

IMNSHO, there is rarely a case where double brackets are needed (I never use them).

The double brackets are not part of the POSIX definition of the shell, and thus are less portable.
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