How to use sed to replace only the first occurrence in a file?

Question

I would like to update a large number of C++ source files with an extra include directive before any existing #includes. For this sort of task, I normally use a small bash s

Answer 1

I finally got this to work in a Bash script used to insert a unique timestamp in each item in an RSS feed:

        sed "1,/====RSSpermalink====/s/====RSSpermalink====/${nowms}/" \
            production-feed2.xml.tmp2 > production-feed2.xml.tmp.$counter

It changes the first occurrence only.

${nowms} is the time in milliseconds set by a Perl script, $counter is a counter used for loop control within the script, \ allows the command to be continued on the next line.

The file is read in and stdout is redirected to a work file.

The way I understand it, 1,/====RSSpermalink====/ tells sed when to stop by setting a range limitation, and then s/====RSSpermalink====/${nowms}/ is the familiar sed command to replace the first string with the second.

In my case I put the command in double quotation marks becauase I am using it in a Bash script with variables.