There are several tools and techniques that go along with the
editor, all of which are relatively easy once you
because they are all based on the editor.
In this section we will give some fairly cursory examples
more to indicate their existence than to provide
More information on each can be found in
Sometimes you want to find all occurrences of some word or pattern in
a set of files, to edit them
or perhaps just to verify their presence or absence.
It may be possible to edit each file separately and look
for the pattern of interest, but if there are many files
this can get very tedious,
and if the files are really big,
it may be impossible because of limits in
was invented to get around these limitations.
The search patterns that we have described in the paper are often
called `regular expressions', and
That describes exactly what
it prints every line in a set of files that contains a
grep \(fmthing\(fm file1 file2 file3 ...
finds `thing' wherever it occurs in any of the files
also indicates the file in which the line was found,
so you can later edit it if you like.
The pattern represented by `thing' can be any
pattern you can use in the editor,
use exactly the same mechanism for
It is wisest always to enclose the pattern in the
single quotes \(fm...\(fm if it contains any non-alphabetic
characters, since many such characters also mean something
If you don't quote them, the command interpreter will
try to interpret them before
There is also a way to find lines that
grep -v \(fmthing\(fm file1 file2 ...
must occur in the position shown.
it is possible to do things like selecting all lines that
contain some combination of patterns.
For example, to get all lines that contain `x' but not `y':
grep x file... | grep -v y
(The notation | is a `pipe',
which causes the output of the first command to be used as
input to the second command; see [2].)
If a fairly complicated set of editing operations
is to be done on a whole set of files,
the easiest thing to do is to make up a `script',
i.e., a file that contains the operations you want to perform,
then apply this script to each file in turn.
For example, suppose you want to change every
`Unix' to `UNIX' and every `Gcos' to `GCOS' in a large number of files.
Then put into the file `script' the lines
to take its commands from the prepared script.
Notice that the whole job has to be planned in advance.
And of course by using the
command interpreter, you can
cycle through a set of files
automatically, with varying degrees of ease.
is a version of the editor with restricted capabilities
but which is capable of processing unlimited amounts of input.
copies its input to its output, applying one or more
editing commands to each line of input.
As an example, suppose that we want to do the `Unix' to `UNIX'
but without rewriting the files.
sed \(fms/Unix/UNIX/g\(fm file1 file2 ...
to all lines from `file1', `file2', etc.,
and copies all lines to the output.
in such a case is that it can be used
All the output can be collected in one place,
either in a file or perhaps piped into another program.
If the editing transformation is so complicated
more than one editing command is needed,
commands can be supplied from a file,
with a slightly more complex syntax.
To take commands from a file, for example,
sed -f cmdfile input-files...
has further capabilities, including conditional testing
and branching, which we cannot go into here.