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Full Discussion: Preview what would execute in my shell script
Top Forums Shell Programming and Scripting Preview what would execute in my shell script Post 302425566 by Corona688 on Friday 28th of May 2010 12:48:48 PM
Old 05-28-2010
The shell's flexibility makes it hard to make a good general-purpose dry-run function. You can embed things that modify or execute things inside parameters as easily as anywhere else, so your method -- and most methods -- won't work in situations like these:
Code:
# command1 and command2 will still be executed
$PREVIEW grep needle haystack | command1 | command2
# command4 will still execute
$PREVIEW command3 `command4`
# N will still be incremented
$PREVIEW echo $((N++))

One way to do it may be to embed code in a here-document. There'd be a a lot of fiddly escaping involved to prevent variables and backticks from still evaluating right at runtime.
Code:
TMP=`mktemp`

# Open FD 5 writing to temp file
exec 5>"$TMP"
# Open FD 6 reading from temp file
exec 6<"$TMP"
# Delete temp file.  FD 5 and 6 will remain valid until closed.
rm "${TMP}"

cat <<EOF >&5
        # This won't run at all
        grep needle haystack | command1 | command2
        # command4 will still execute
        command3 `command4`
        # command4 won't execute
        command3 \`command4\`
        # N will still be incremented
        echo $((N++))
        # N will not be incremented
        echo \$((N++))
EOF

if [[ "${DRY_RUN}" == "Y" ]]
then
# Just print the contents of the temp file to the screen
        cat <&6
else
# Execute the script inside a new shell
        bash <&6
fi

Last edited by Corona688; 05-28-2010 at 01:59 PM..
 

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LEARN ABOUT PHP

mb_strstr

MB_STRSTR(3)								 1							      MB_STRSTR(3)

mb_strstr - Finds first occurrence of a string within another

SYNOPSIS

       string mb_strstr (string  $haystack, string  $needle, [bool  $before_needle = false], [string  $encoding = mb_internal_encoding()])

DESCRIPTION

       mb_strstr(3)  finds  the first occurrence of $needle in $haystack and returns the portion of $haystack. If $needle is not found, it returns
       FALSE.

PARAMETERS

	      o $haystack
		- The string from which to get the first occurrence of $needle

	      o $needle
		- The string to find in $haystack

	      o $before_needle
		- Determines which portion of $haystack this function returns. If set to TRUE, it returns all of $haystack from the  beginning	to
		the  first  occurrence	of  $needle  (excluding needle). If set to FALSE, it returns all of $haystack from the first occurrence of
		$needle to the end (including needle).

	      o $encoding
		- Character encoding name to use. If it is omitted, internal character encoding is used.

RETURN VALUES

	Returns the portion of $haystack, or FALSE if $needle is not found.

SEE ALSO

       stristr(3), strstr(3), mb_stristr(3).

PHP Documentation Group 													      MB_STRSTR(3)
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