Gnu sed

Gnu sed performs search/replace within stdin or files.
See also bsd sed.

Overview

sed lets you manipulate text streams using commands.

example commands:

# 's' command search/replaces text
echo 'foo_bar_baz' | sed 's/bar/BAR/g'
> 'foo_BAR_gaz'

# 'i'/'a' commands prepend/append newlines to each line
echo 'foo\nbar\nbaz' | sed 'i \my newline'
> my newline
> foo
> my newline
> bar
> my newline
> baz

By default, all commands operate on every line.
You can use addresses to limit the scope of a command.

# Limit scope of 'i' command to lines matching /bar/
echo 'foo\nbar\nbaz' | sed '/bar/i \my newline'
> foo
> my newline
> bar
> baz

Usage

# Replace 'aaa' with 'bbb'
cat echo "aaa_stuff_aaa" \
    | sed 's_aaa_bbb_g'


# Regex
cat echo "aaa_stuff_aaa" \
    | sed -E 's_[a]*_b_g'

# Group matching (\2 is a variable that refers to the
# second match group. In this case, 'stuff'
cat echo "aaa_stuff_aaa" \
    | sed -E 's_\([a]*\)\(stuff\)_\2\n'


# Replace file contents
sed -i"bak"  "s_aaa_bbb_g" /path/to/file