sed - nx.beandog.org

====== sed ======

  * [[awk]]
  * [[grep]]
  * [[sed examples]]

Sed is a string editor program.  It can manipulate data using regular expressions.

  * [[http://www.gnu.org/software/sed/manual/html_node/Invoking-sed.html#Invoking-sed|Invoking sed]]
  * [[http://www.gnu.org/software/sed/manual/html_node/Examples.html#Examples|Examples]]
  * [[http://sed.sourceforge.net/sedfaq3.html#s3.2|Common one-line sed scripts]]
  * [[http://sed.sourceforge.net/grabbag/|seder's grab bag]]
  * [[http://www.ibm.com/developerworks/linux/library/l-sed2/index.html|Common threads: Sed by example]]
  * [[http://sed.sourceforge.net/sed1line.txt|One-line scripts for sed]]

The basic syntax for sed is ''sed SCRIPT INPUTFILE'' where a SCRIPT is the format used to replace or modify.

If you want to pass options, then the format is ''sed OPTIONS SCRIPT INPUTFILE''

Here is a simple example that removes spaces from a string:

<code>
echo foo bar | sed 's/\ //' # returns foobar
</code>

In the script, characters that would be parsed by the shell need to be escaped.

== Basic syntax ==

Here are some of the common arguments that will be used.

First of all, if you are passing arguments, and not just a script, then you need to specify which argument is the script.  The same example as before, using **''-e''** or **''--expression''** would look like this:

<code>
echo foo bar | sed -e 's/\ //' # returns foobar
</code>

== Scripting from a file ==

You can load a script from a file instead of passing it as an expression.  The syntax is the same, you still need to escape characters.

<code>
echo 's/\ //' > /tmp/rules.txt
echo foo bar | sed -f /tmp/rules.txt 
</code>

== Edit a file ==

You can have sed update the file directly:

<code>
echo foo bar > /tmp/foobar.txt
sed -e 's/\ //' /tmp/foobar.txt -i
</code>

** BSD / Darwin: ** BSD's version of sed will use an extension given to ''-i'' to create a backup file of the original.  So ''sed -i .bar foo'' will create ''foo.bar'' while updating ''foo'' as well.  By comparison, GNU sed accepts an optional argument if given directly after the option: ''sed -i.bar''.

To workaround the inconsistency, you have two options.  Pass an empty character after the option for both:

<code>
sed -i'' ...
</code>

Or, pass ''-i'' as the last option:

<code>
sed ... -i
</code>

== Regular expressions ==

If you need to use regular expressions in the same format that egrep does, use **''-r''** as well.

== Global replacement ==

By default, sed will only replace the first occurrence of a match.  With a regexp modifier, you can have it do more.

Use ''g'' to replace all instances:
<code>
echo foo bar | sed 's/o//' #returns fo bar
echo foo bar | sed 's/o//g' #returns f bar
</code>
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