This illustrates why?sed?scripts get the reputation for obscurity. I could be perverse and show you the example that will search for all lines that start with a "g," and change each "g" on that line to an "s:"

sed '/^g/s/g/s/g'

Adding a space and using an underscore after the substitute command makes this?much?easier to read:

sed '/^g/ s_g_s_g'

Er,I take that back. It's hopeless. There is a lesson here: Use comments liberally in a?sed?script under SunOS. You may have to remove the comments to run the script under a different operating system,but you now know how to write a?sed?script to do that very easily! Comments are a Good Thing. You may have understood the script perfectly when you wrote it. But six months from now it could look like modem noise.

You can specify a range on line numbers by inserting a comma between the numbers. To restrict a substitution to the first 100 lines,you can use:

sed '1,100 s/A/a/'

If you know exactly how many lines are in a file,you can explicitly state that number to perform the substitution on the rest of the file. In this case,assume you used?wc?to find out there are 532 lines in the file:

sed '101,532 s/A/a/'

An easier way is to use the special character "$," which means the last line in the file.

sed '101,$ s/A/a/'

The "$" is one of those conventions that mean "last" in utilities like?cat -e,?vi,and?ed. "cat -e" Line numbers are cumulative if several files are edited. That is,

sed '200,300 s/A/a/' f1 f2 f3 >new

is the same as

cat f1 f2 f3 | sed '200,300 s/A/a/' >new

You can specify two regular expressions as the range. Assuming a "#" starts a comment,you can search for a keyword,remove all comments until you see the second keyword. In this case the two keywords are "start" and "stop:"

sed '/start/,/stop/ s/#.*//'

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