противоположно большему (opposite of more)
INPUT PREPROCESSOR
You may define an "input preprocessor" for less. Before less
opens a file, it first gives your input preprocessor a chance to
modify the way the contents of the file are displayed. An input
preprocessor is simply an executable program (or shell script),
which writes the contents of the file to a different file, called
the replacement file. The contents of the replacement file are
then displayed in place of the contents of the original file.
However, it will appear to the user as if the original file is
opened; that is, less will display the original filename as the
name of the current file.
An input preprocessor receives one command line argument, the
original filename, as entered by the user. It should create the
replacement file, and when finished, print the name of the
replacement file to its standard output. If the input
preprocessor does not output a replacement filename, less uses
the original file, as normal. The input preprocessor is not
called when viewing standard input. To set up an input
preprocessor, set the LESSOPEN environment variable to a command
line which will invoke your input preprocessor. This command
line should include one occurrence of the string "%s", which will
be replaced by the filename when the input preprocessor command
is invoked.
When less closes a file opened in such a way, it will call
another program, called the input postprocessor, which may
perform any desired clean-up action (such as deleting the
replacement file created by LESSOPEN). This program receives two
command line arguments, the original filename as entered by the
user, and the name of the replacement file. To set up an input
postprocessor, set the LESSCLOSE environment variable to a
command line which will invoke your input postprocessor. It may
include two occurrences of the string "%s"; the first is replaced
with the original name of the file and the second with the name
of the replacement file, which was output by LESSOPEN.
For example, on many Unix systems, these two scripts will allow
you to keep files in compressed format, but still let less view
them directly:
lessopen.sh:
#! /bin/sh
case "$1" in
*.Z) TEMPFILE=$(mktemp)
uncompress -c $1 >$TEMPFILE 2>/dev/null
if [ -s $TEMPFILE ]; then
echo $TEMPFILE
else
rm -f $TEMPFILE
fi
;;
esac
lessclose.sh:
#! /bin/sh
rm $2
To use these scripts, put them both where they can be executed
and set LESSOPEN="lessopen.sh %s", and
LESSCLOSE="lessclose.sh %s %s". More complex LESSOPEN and
LESSCLOSE scripts may be written to accept other types of
compressed files, and so on.
It is also possible to set up an input preprocessor to pipe the
file data directly to less, rather than putting the data into a
replacement file. This avoids the need to decompress the entire
file before starting to view it. An input preprocessor that
works this way is called an input pipe. An input pipe, instead
of writing the name of a replacement file on its standard output,
writes the entire contents of the replacement file on its
standard output. If the input pipe does not write any characters
on its standard output, then there is no replacement file and
less uses the original file, as normal. To use an input pipe,
make the first character in the LESSOPEN environment variable a
vertical bar (|) to signify that the input preprocessor is an
input pipe. As with non-pipe input preprocessors, the command
string must contain one occurrence of %s, which is replaced with
the filename of the input file.
For example, on many Unix systems, this script will work like the
previous example scripts:
lesspipe.sh:
#! /bin/sh
case "$1" in
*.Z) uncompress -c $1 2>/dev/null
;;
*) exit 1
;;
esac
exit $?
To use this script, put it where it can be executed and set
LESSOPEN="|lesspipe.sh %s".
Note that a preprocessor cannot output an empty file, since that
is interpreted as meaning there is no replacement, and the
original file is used. To avoid this, if LESSOPEN starts with
two vertical bars, the exit status of the script becomes
meaningful. If the exit status is zero, the output is considered
to be replacement text, even if it is empty. If the exit status
is nonzero, any output is ignored and the original file is used.
For compatibility with previous versions of less, if LESSOPEN
starts with only one vertical bar, the exit status of the
preprocessor is ignored.
When an input pipe is used, a LESSCLOSE postprocessor can be
used, but it is usually not necessary since there is no
replacement file to clean up. In this case, the replacement file
name passed to the LESSCLOSE postprocessor is "-".
For compatibility with previous versions of less, the input
preprocessor or pipe is not used if less is viewing standard
input. However, if the first character of LESSOPEN is a dash
(-), the input preprocessor is used on standard input as well as
other files. In this case, the dash is not considered to be part
of the preprocessor command. If standard input is being viewed,
the input preprocessor is passed a file name consisting of a
single dash. Similarly, if the first two characters of LESSOPEN
are vertical bar and dash (|-) or two vertical bars and a dash
(||-), the input pipe is used on standard input as well as other
files. Again, in this case the dash is not considered to be part
of the input pipe command.
