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copied!<p>Assuming '<code>identify filename</code>' is itself a command, then I think you'll need to use Perl for this. In the best Perl inscrutable style:</p> <pre><code>while (<>) { s/#(\w+)#/my $x = qx%identify $1%; chomp $x; $x/e; print; } </code></pre> <p>This reads a line of input ('<code><></code>') into the implicit variable '<code>$_</code>'; the next line applies a substitute operation to the implicit variable - more details in a moment - and then the '<code>print</code>' prints the implicit variable.</p> <p>As to the substitute operation '<code>s///</code>', the first part looks for a hash '#', a series of one or more 'word' characters - alphanumerics or underscore - and another hash, making the identified file name available as '<code>$1</code>'. The second part is the replacement string. After the third slash is the modifier '<code>e</code>' which means 'execute the replacement as bit of Perl'. And the relevant bit of Perl is:</p> <pre><code>my $x = qx%identify $1%; chomp $x; $x </code></pre> <p>The first part executes the command '<code>identify filename</code>' if the string between the hash marks is 'filename', saving the output, newline and all, in local variable $x. The '<code>chomp</code>' operation removes the newline; the final '<code>$x</code>' yields a value - the string that was output by the 'identify' command. (Somewhat to my surprise, Perl does not allow a simpler looking: <code>s/#(\w+)#/chomp qx%identify $1%/e</code>; the error was '<code>Can't modify quoted execution (``, qx) in chomp at xx.pl line 3, near "qx%identify $1%)"</code>'.)</p> <p>Consider the 'identify' command:</p> <pre><code>echo "identified file $1 as $PWD/$1" </code></pre> <p>Now consider the input line:</p> <pre><code>abc#def#ghi </code></pre> <p>The output is:</p> <pre><code>abcidentified file def as /Users/jleffler/tmp/soq/defghi </code></pre> <p>(where <code>/Users/jleffler/tmp/soq</code> happened to be my current directory while running the command).</p> <p>Rather less inscrutably:</p> <pre><code>while (my $line = <>) { if ($line =~ m/#(\w+)#/) { my $identity = qx{identify $1}; chomp $identity; $line =~ s/#\w+#/$identity/; } print $line; } </code></pre> <p>Certainly not as compact, but the explanation is very similar.</p> <p>Note that the initial edition is not the most compact form possible. Consider this version:</p> <pre><code>perl -p -e 's/#(\w+)#/my $x = qx%identify $1%; chomp $x; $x/e' </code></pre> <p>The '-p' option places the script (the argument to '-e') in a read, execute, print loop (REPL).</p> <p>That's one of the wonders of Perl - TMTOWTDI (pronounced 'tim-toady') - There's More Than One Way To Do It.</p>

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